Xantia V6 broken exhaust (update: and rough low rpm running)

[stevieb]

A quick update on mine. It'd been running mostly fine since I swapped back to the secondhand coilpack, then I popped out to the car earlier this evening to check my fuel pressure regulator (pull the vacuum hose to make sure nothing is escaping from the regulator suggesting a diaphragm leak), and noticed the tappet noise was completely gone, BUT the exhaust was REALLY growly. This was from a very cold start too. I dashed into the house to get my phone to record this phenomenon and realised the exhaust reverberation was so strong the windows in the (house) front door were rattling, as was the handle. By the time I'd got back to the car the ticking noise was beginning again and the exhaust snarl was subsiding. Very odd.

While I think of it Simon, the dips in revs you suffer after blipping the throttle - have you changed the MAP sensor? And if so, have you used a genuine Bosch one, or an Intermotor one? I only ask as I replaced my original Bosch one with an Intermotor one some years ago and last year during the Invisible Caravan issue found that it had failed completely - all readings were way beyond the working range the ECU would expect to see. Running the multimeter over the original MAP sensor showed that was in considerably better condition, readings-wise, than the newer one. I bought a genuine Bosch one (I think from Euro Car Parts), and it helped enormously with tickover and low rpm gremlins.

[Mandrake]

You see, I wonder if one of mine is a bit gummy and sometimes dribbling rather than spraying. This would definitely cause the engine note to change and might even result in a certain amount of unburnt fuel finding its way into the exhaust and igniting there, causing the rough, growly noise I hear when things are bad. I know that even after a long motorway journey, if I find my way into some town traffic when the noise is there I also see a lot of vapour still coming from the exhaust - you wouldn't normally expect this from an exhaust that's well and truly warmed-up.

Funny you should mention a lot of vapour from the exhaust - I have that too, but only intermittently...

Mainly visible on days below about 6 degrees, but as you say even when the car is well and truly warmed up there will sometimes be enough of a cloud of vapour from the tail pipe (un-burnt fuel ? smoke ? steam ?) while stopped at the traffic lights that a strong gust of wind will blow it past the front of the car so I will see it. (and I can see it in the rear view mirror)

There might be noticeable vapour for a few seconds then it stops for a while then it will be back again.

When I look at cars around me usually none of them or maybe only one or two will have any visible emission from the tailpipe, so I don't think its normal, even though when I've asked about this before on the forum most people seem to think its just condensation in the exhaust system. (I'm sure its that as well, at least when starting off from cold, but it shouldn't still be there after a long drive)

The rough growly noise you hear is probably just that of a misfire - it tends to make the exhaust note boomy as well, although I'm not quite sure why - but back when I was having really bad wide throttle misfires it always made the exhaust really boomy sounding.

For laughs today I epoxied a couple of cracks in my second hand coil pack and fitted it to the car, removing my "new" coil pack - initial results seemed promising as using a normal amount of throttle to accelerate away in 1st resulted in wheelspin on dry seal whereas normally its very hard to get any wheel spin out of it unless I'm on a lock and at first it seemed like there was a definite improvement over the first couple of miles driving with the car being very sprightly.

But it was short lived - it started getting intermittently sluggish again and started exhibiting what I'd call "rubber throttle" syndrome where the throttle response feels like there is a big block of rubber between your foot and the pedal...and then it got better again, then worse, then better, sometimes there was as little as 30 seconds between sluggish as hell and zippy as hell. So basically the coil pack didn't make any long term improvement.

I've been thinking a lot about the symptoms of your car and mine, doing more reading, watching some more diagnostic videos and am coming to the conclusion that we could both be dealing with one or more intermittently sticking/clogged injectors which is causing a lean misfire...

I know for a fact my compressions are good (210 psi +/- 3 psi on a dry test) the ignition system has been gone over so many times that it can't possibly be at fault now - new plug leads definitely improved the average performance dramatically compared to its worst 6 months ago but some of the variability in performance is intermittently back again. Spark plugs are good, and clean, I have three different coil packs to choose from, and I know for certain its not the ECU either, and I've tested the ignition wiring in the harness as well - that's the entire ignition system eliminated as far as I can see.

I also know that the car seems to perform better and more consistently with injector cleaner added than plain fuel, although it doesn't completely cure it.

I know my oxygen sensor doesn't warm up properly and I WILL be replacing that in the next month or two, but I don't think its the major issue either.

Pretend for a moment that one (it would only take one) injector is intermittently sticking closed or not fully opening - that cylinder would suffer a lean misfire, the excess oxygen would register with the oxygen sensor causing the ECU to richen all the cylinders thus rich running (on 5 cylinders) and poor fuel consumption. Also a lean misfire can trigger knocking as well which would cause the timing to get retarded causing further performance loss.

One thing I noticed today is that during the first 30 seconds after a cold start while cold start enrichment is still active, I can floor the accelerator pedal and there is no hesitation at all, it revs beautifully. A couple of minutes later (after the cold start enrichment is dialled back) if I floor the accelerator the stumble is back. A lean misfire on one cylinder when I floor it due to an intermittent flow problem with an injector ?

I have done an injector balance test ONCE nearly a year ago and it was ok during the test, but given how intermittent the symptoms can be I may have just caught it during one of its good spells. There are definitely times when even just at idle the engine is running unbalanced like it has a single cylinder misfire, and other times when it is idling rock steady and smooth.

I came across the following discussion thread when trying to find out if injectors could ever have intermittent faults:

http://www.peugeotforums.com/forums/406 ... ers-18068/" onclick="window.open(this.href);return false;

Symptoms sound familiar ? A single cylinder misfire is a bit more obvious on a 4 cylinder I think - on a 6 cylinder loosing one cylinder is a smaller percentage drop in power so a bit harder to notice - I find it difficult to tell for sure if there is a misfire occurring or not.

I'll cut to the chase, he tried a coil pack and that didn't fix it, but replacing the injectors with second hand ones did fix it.

For some time I've been thinking seriously (if the symptoms returned) about getting my injectors professionally tested and ultrasonic cleaned. Perhaps somewhere like this ? (Anyone tried these guys ?)

http://www.injectortune.co.uk" onclick="window.open(this.href);return false;

Of course it makes me somewhat nervous sending away my only set of injectors and leaving the car off the road for a week, (not to mention trying to get all the manifold in and out in between showers of rain at the side of the road, even if the weather has been unseasonably warm up here) but I have an MOT in less than 6 months and a still undiagnosed intermittent misfire which almost certainly WILL fail the emissions test this time if exhibiting symptoms during the test. (It barely scraped in last time)

My other choice is to take a punt on a cheap set of second hand injectors from a scrapped car as you did - at least the car wouldn't be off the road for more than a few hours, and I could always send my originals away for cleaning if the second hand ones weren't ideal either...(for all I know they could be more clogged or intermittent than mine!)

Maybe the next step for you is to try your second hand injectors ? It's one of the very few things you haven't already tried yet as well. I wonder if it would be worth getting them properly cleaned (if they're off an old scrapped car there's no knowing how balanced they are and whether they also have problems) or would you just fit them and see how you go ?

If you do I would be very interested to know the outcome.

I think it's as you've found Simon, anything less than ideal combustion gets detected by the oxygen sensor and results in the ECU making changes elsewhere to compensate. As you say, it's pretty crude

Yes, I think when a misfire occurs the ECU does start winding the mixture up or down incorrectly in response to the oxygen sensor reading, then when the misfire stops it gradually corrects it again - thus the transitions between poor and good running - when sluggish you can sometimes feel its sluggish for many seconds then it starts to pick up and then becomes normal again over a period of 10-20 seconds. I think that is the mixture being corrected back in the other direction.

[Mandrake]

These are my three front plugs Simon - how do they compare with yours?

You can see the state of my spark plugs last time I checked them here: (along with the previous type that were fouled)

http://www.frenchcarforum.co.uk/forum/v ... 40#p382440" onclick="window.open(this.href);return false;

[Mandrake]

While I think of it Simon, the dips in revs you suffer after blipping the throttle - have you changed the MAP sensor? And if so, have you used a genuine Bosch one, or an Intermotor one? I only ask as I replaced my original Bosch one with an Intermotor one some years ago and last year during the Invisible Caravan issue found that it had failed completely - all readings were way beyond the working range the ECU would expect to see. Running the multimeter over the original MAP sensor showed that was in considerably better condition, readings-wise, than the newer one. I bought a genuine Bosch one (I think from Euro Car Parts), and it helped enormously with tickover and low rpm gremlins.

Yes I have changed the MAP sensor.

Like you I first fitted a cheap Intermotor one (about £20) but it was dead on arrival (literally!) so I sent that one back. I then fitted a brand new Bosch one - no real change.

I've swapped them back and forth a few times with no real change so I've actually lost track of which one is in the car now - they look absolutely identical right down to the logo and moulding!

So no the dip in revs is not MAP sensor nor TPS as that has also been replaced with a genuine part. (Again, they can't be visually distinguished, apart from one being slightly dirtier)

I think you're probably right about a return of carbon build up in the throttle butterfly area - it may well be the cause of the dip in engine revs when very gently tapping the throttle, but I don't think its related to the main issues.

On the other hand the stumble that occurs when flooring the throttle at idle I believe is a lean misfire. (See two posts ago) Quite different symptoms.

[stevieb]

Good timing Simon - I have news that should answer a lot of your questions and comments above. You'll be pleased to hear I got through few jobs yesterday afternoon whilst we had a few hours of dryness.

Firstly I had to switch back to my factory coilpack in a posh bit of Leeds city centre - the trip up there via Wakefield (50 miles at most) got through about a tenners-worth of fuel with the second-hand coilpack, so I was determined to swap back. I was even more certain when I popped the bonnet and could see moisture pockets behind the epoxy where the two cracks were. Unsurprisingly, the car ran better when I switched back, but the sudden gain didn't materialise - maybe it hadn't had enough rest time.

Anyway, I got home from Leeds (via Bradford) with things running a bit better, and after I'd typed up my work got stuck into some serious work. To go with the front ones, these are my rear plugs:



I'm of the opinion that these plugs are way beyond their best now. I had thought they'd done around 25,000 miles. Working it out properly, I think it's more like 50,000 miles. They were guaranteed for 100,000, so I guess in a wasted spark system they work twice as hard and have effectively done 2x50,000 miles=100,000 miles. Time for a change.

In my current "clean up every electrical terminal in sight" frame of mind I decided to clean out the terminals on the rear bank cassette and HT leads. The leads were fine, with their brass-coloured connectors all in good order. The springs inside the rubber boots were fine too - dull, but not badly so. These are the original factory ones too, so I was impressed. Then I pulled off the boots and looked at the contact patch between the springs and the bottom of the cassette. Now, keep in mind the three plugs above (shown left to right from belts to flywheel). The belt end one was dull - not corroded, just dull. The middle and fly wheel ones both looked like this:



The second pic show what a tiny bit of action with a flat-blade screwdriver did. Needless to say, I shifted ALL the black cack.

That was the first job done - the priority. After this I got stuck into swapping the injectors - it's not a bad job at all really - messy with petrol being spilled, but far from difficult. Once that inlet manifold is off it's just a case of disconnecting the two fuel hoses, undoing the bolts and lifting them out (via a lot of wiggling and the disconnection of the front rocker cover breather hose - mine was brittle - mine broke - more heatshrink tubing...). Re-fitting them was a bit different and requires more patience than I had at this stage (the sky had gone black and there was snow in the air, so panic was kicking-in). All the O-rings need oiling or greasing to ease them in - the injectors should go back into the rail by hand, not requiring a vice - I put a crack in the little yellow cap of one because I was rushing, so I rejected it.

Basically I considered all three of the rears to be scrap. Two of the quiet front three went into the rear rail, with one of the unknown secondhand ones in the middle. The front rail was ALL unknown secondhand ones. Oh yeah, I should say I'd run the multimeter over them all first - all gave similar impedance readings, within a few tenths of an ohm (the engine ones were still warm, which might have explained why these were slightly higher than the others.

Put it all back together, new inlet manifold gasket, nothing else changed. A few seconds turning over while the fuel pressure found its way through the now dry injectors and immediately the car is different. A little bit louder than those old "good days", but a lot quieter and less growly than the bad days. A little bit more vibration than I was used to, but nothing major and probably down to the unknown injectors unsticking as well as the ECU adjusting. Then I realised the car was back to being the car I bought with 40-odd thousand on the clock. I daren't take it out for a run last night for fear of disappointment.

Today I've been doing some running about for a mate - short journeys around town - the kind of conditions that were guaranteed to bring on some "bad day" problems. But nothing. Consistent all day, powerful, smooth, effortless.... It's the car it's supposed to be...

I'd love to tell you what fixed it, but I bet you've already come to your own conclusion Simon, especially as my findings confirm your thinking which confirmed my thinking which... etc....

I DID notice when the engine was first running that the ticking had moved - there was still a light ticking from beneath the inlet manifold - either genuine tappet noise or the unknown middle injector. However, the front three (unknowns) all tick merrily along like clocks in a clock shop, so I guess they're all a bit noisy - whether through sitting idle or a problem I wouldn't like to say, but the car is transformed. The movement of this noise in such a noticeable fashion confirms my belief that it was injector noise and not tappet noise (or maybe it was both). I videoed this phenomenon, but the whole noise is kinda drowned out by the recirculation solenoid thingy which is also now ticking merrily along - it's been a long time since I last heard it working so much - recently I only ever heard it on a good day.

I may get a bit of motorway action over the weekend (subject to working out the front suspension clock I now have), and I'll report back on any changes if I have any. Otherwise, I definitely have motorway time on Monday morning through the lovely 50mph roadworks test track - I'll miss them when they're gone... - and again, I'll post any updates. I may run a bottle of injector cleaner or some V-Power through to see if the noise in those injectors goes - if it does, and stays gone, then I think I can say I've solved the problem at last.

Now for some new plugs, via another suspension fix

[stevieb]

I think I should add a few things I'd forgotten to mention in my monumental post.

Firstly, the "kick" that I had at low revs/high gear has also now gone. Pick-up from low revs is smooooooooth now, as well as high rpm acceleration - no more surging at 3500rpm - it just wafts along like a good un'. After I was done at my mates this evening I took the car for a blast - a little suburban driving, then onto the 70mph dual carriageway to the M1 (junction 33 for those who know it). At no point on that journey, in howling winds and driving rain, did the car miss a beat. It pulls from tickover in fifth once more

There's a sense that some of the cylinders are slightly lumpy - the cause of the slight increase in vibration at tickover - but no worse than a healthy carburettor/coil/distributor setup did on a damp day. I expect some cleaning gloop and a good old Italian tune-up should fix it. New plugs certainly will.

Another improvement, which is something I'd sometimes experienced on the good days that also fits with your "rubber throttle" comment Simon, is that the revs now pick up the instant I touch the throttle - frequently today I've found myself with rising revs before I've reached the biting point of the clutch, just because I'm used to needing a bit more right boot before I dare let up the clutch pedal (manual, remember?) I think the last time I felt this much increase in response was when I replaced my first TPS and found the car actually responded to the actions of my right foot for a change. Mind you, the sticky throttle body causes this problem too, probably upsetting the zero-point of the TPS - basically the same problem, just with a different cause.

On the subject of injectors sticking closed, I've read in the past about the issues of injectors sticking open too. Imagine in the ES9J4 with its crude set of sensors, an injector is dribbling in between cycles - creating a rich choke-like mixture in one cylinder - and now imagine what the ECU sees. Firstly it sees an over-rich mixture at the oxygen sensor - there's only one cylinder that's causing it, but it's there. So all six cylinders are leaned off, ever so slightly, so compensate. Now the ECU is seeing a happy mixture at the oxygen sensor, but power is lost due to five cylinders running lean. It's all very marginal, but across a V6, it's going to be noticeable. Add to that the fact that the rich cylinder is still rich (just a little less so now) and running roughly, partly because it's rich and partly because the between-cycle dribbles of fuel won't be properly atomised as they leave the injector and will upset the combustion in the cylinder, and you can see another source of power loss, this time with even more potential for increased mpg.

My thought is that I had an injector that was sticky, full stop. Sometimes it was stuck closed and I was losing a cylinder, possibly with the other five being enriched to compensate at the oxygen sensor. Other days I had the injector stuck open, dribbling, causing rough running in one cylinder and leanness in the rest - loss of power and a growly exhaust note into the bargain. Either way, that problem seems to have abated, at least for a while, by introducing some different injectors.

Of course, none of the injector debate answers the strange coilpack behaviour. I think I had this as a secondary problem, throwing me off the scent. My original coilpack is the stronger of the two I own, but either weakened plugs or the crud in the pics of the cassette above, was sufficient to put strain on it, and this strain would begin to tell over time. I think the secondhand coilpack was a red herring - sometimes, when it was dried-out inside, it would perform faultlessly, outperforming my own one. On damp days (or even after a long run, as things cooled down again), the cracks would draw moisture in and this is when it began to misbehave - again, ageing sparks must've added extra load not to mention the constant adjustments demanded by an ECU trying to compensate for a misbehaving injector (the symptoms in-turn exaggerated by a weaker spark...), and it's no surprise this one failed sooner each time.

If I were you Simon I'd be tempted with the injector cleaning option. I priced it up for my spare six last summer and it came in around £90-odd. If you can afford it, it'd probably pay itself back in a couple of months. The only reason I dismissed the idea last year was that the car had only just scraped the MoT emissions a few months before, and not knowing the state of the rest of the fuelling system (and the dubious nature of my throttle body and fuel filter butchery), I opted for Terraclean as a full-on chemical flush. Knowing my oxygen sensor is tighter than a tight thing in Tightsville I didn't fancy the job of swapping it, so cleaning it this way seemed appealing. Like you, I'd also had improvements in performance with injector cleaner and high-octane fuel so I knew something was amiss with the fuel side of things. Terraclean did the trick for a few months, but I guess if the injector is mechanically failing, there's only so much that can be done by cleaning it. My Terraclean treatment cost £100 and the difference was clear, so I don't begrudge paying it. In your case however, if you're fitting a new oxygen sensor, and you have a good knowledge of the rest of your fuel/air system (with no butchery marks), I'd be tempted to just get the injectors done. All the specialist places claim not to clean failed injectors - they'll let you know if one isn't performing within spec and should be binned - so at least you'll know you're not putting duff ones back in. I took a chance on mine, simply because things were getting daft and I can't afford to run the car at any less than 30-odd mpg in my job, and so far it's helped. If I'd fitted six freshly cleaned ones though...

[Mandrake]

Hi Steve,

That's very encouraging news indeed! I was hoping you would try fitting your spare injectors but didn't expect it to be so soon.

There's far too much there to quote each individual sections so I'll reply to the whole lot at once.

Before I do that I'll quickly update you on the coil pack swap experiment I did yesterday. As I posted at the time the second hand coil pack started good but went down hill quickly, with intermittent poor performance that left it worse, certainly no better than the other coil pack.

Today we did a quick shopping run - a mile each way with an hours wait (for the car) in between. On the way over it started off ok but by the time we were half way there I could feel it was well down on power complete with "rubbery throttle response". On the way back it was absolutely dreadful.

Dead, dead, dead. No low rpm power or pick up at all and completely rubbery throttle response. Not particularly noisy or rough, just a complete lack of any sort of power or throttle response low down. Small hills that I drive over many times a week which it will usually accelerate up responsively in 3rd at 1500 rpm with a light touch of the throttle today it wouldn't accelerate up at all with any amount of throttle, short of kicking down a gear.

Sure, it climbed the hill but going from 10% throttle to 70% throttle did basically nothing except produce some additional exhaust (or maybe induction) boom. It felt like a big heavy tub of lard. If I had to guess I would say it felt like it was down two cylinders, at least when putting your foot down any decent amount.

Obviously I couldn't let it stay this way, fuel usage would have been through the roof (if I could measure it!) and if it was really an ignition misfire it could damage the cat. Fortunately the weather cleared up this afternoon (a balmy 7 degrees with sunshine and blue skies!) so out came the epoxied second hand coil pack and back in went the new (well, one year old) one I had removed yesterday.

I didn't disconnect the battery nor try any key reset technique, and I was careful not to disturb anything unrelated like other wiring, including injector wiring. I just whipped the plastic cover off and swapped the coil pack over. I did carefully clean the rubber boots for the front plugs, stretched and checked their springs, lightly greased the inside of the ends of the rubber boots and the top plug lead boots with lithium grease and put it all back together.

What a difference! Large and immediate return in performance to what it had been a few days ago. Sharp throttle response, (most of the time anyway, not always) easy acceleration in 3rd at 1500 rpm etc. I'm not saying its perfect because there is still some fluctuation in performance and it did drop away slightly after heating up on a long drive, but nothing like the absolutely horrendous loss of power this morning on the other coil pack.

So as far as I'm concerned case closed on the coil pack front - the second hand coil pack is faulty. (Sorry KP!) So in a way yesterdays experiment was a big waste of time because all I've really confirmed is that a coil pack I wasn't using anyway seems to have something wrong with it, and I already had the best one in the car, which probably doesn't have anything wrong with it!

That and that there is still the more subtle intermittent variation in performance and throttle response present that I now believe could be injector related.

Ok on to your posts in my next post.

[Hell Razor5543]

I have a suggestion. I don't know if it is feasible, but it could be worth examining. Is it possible to remove (dissolve) the old epoxy from a faulty coil pack, clean it up, and then re-epoxy the coil pack? As there is (at least) one faulty coil pack you wouldn't be any worse off if it didn't work.

EDIT; a bit of research has found that heating epoxy to around 100C turns it a bit rubbery and helps removal. This might be some useful info;

http://kevtris.org/Projects/votraxpss/unpot.html" onclick="window.open(this.href);return false;

[stevieb]

Another minor update between Simon's posts.

I've just had a quick jaunt down that 70mph dual carriageway again, this time for some V-Power. Outbound @ 70mph, possibly with a bit of tail wind assistance = 45mpg. Same road coming back, definitely into the wind = 35-40mpg. The car felt a tiny bit less lively coming back home, but whether this is warm-start blues or the weather conditions (which have been horrendous today) I don't know. I still think the ECU needs to re-learn a lot, and this might just be a part of that.

Oh yeah, the extra vibration at tickover has now gone too.

It's getting there...

[Mandrake]

Regarding your plugs, the centre electrodes do look past their best. I know that type of plug is supposed to have a sharp pointed tip on the centre electrode but it looks like it has eroded away to leave a considerably larger than normal gap. Did you measure the gap ? It's supposed to be exactly 1mm but it looks like a lot more than that to me. Compare that to the size of the gap of my plugs in the picture I posted.

Spark voltage is directly proportional to gap so if the gap is 50% wider than it should be it will take a 50% higher spark voltage under otherwise identical operating conditions! If the coil/leads can't supply a high enough voltage you'll get a misfire under those conditions where a high voltage is required.

Even if the coil can supply the additional voltage due to the larger gap and a misfire doesn't result the higher voltage will place additional dielectric stress on all the insulators in both the coil pack and the plug leads - causing them to potentially fail at a lower mileage than they otherwise would. A smaller correct spark plug gap keeps the voltage down to the range it should be.

So I'd definitely replace the spark plugs when convenient but if its running really well since the injectors were swapped its not urgent. Personally I like the dual electrode ones like those I pictured (and they are the OEM type after all, probably chosen for a reason) but that's just me. As you say a waste spark system will erode the electrodes at twice the normal rate, and the dual electrode plugs are primarily designed to double the life time of the plug by providing two potential gaps. (Only one gap sparks at a time but as that one wears down the other starts sparking and visa versa, so they wear evenly)

Interesting to see the black muck inside the cassette terminals - I don't remember what my original cassette looked like inside - the one that's on the car now is only a few months old so its spotlessly clean of course. In the big picture I doubt that a layer of carbon would make much difference, when you have 60,000 volts available it will just jump through a tiny gap like that, and carbon is a partial conductor anyway. (good to clean it up anyway though)

The coil secondary's have a resistance of 12k ohms, the plug leads 6k ohms and if your spark plugs are resistor types (my current ones are, my previous ones were not) then they are typically 6k ohms as well. So total series resistance for a given coil including both plugs, coil and leads is about 30k ohms, so a little bit more resistance won't make much difference.

On the injectors - glad to hear that they're not too difficult to replace! I didn't think they would be as I had the fuel rails half out when I swapped the fuel pressure regulator over. Is it difficult to completely remove them ? I think if I was sending the injectors away to be cleaned I would want to take the fuel rail right out and give it a good clean inside with carb cleaner.

Sounds like you were right that some of the ticking noise was the injectors! Mine is still silent when cold but there is a definite tick from two different sources when hot - I'm starting to wonder if that is a couple of rear injectors becoming noisy when hot...

Your slightly lumpy idle may just be injector balance is not perfect - you've mixed some of your original injectors with some untested second hand ones, its quite possible that you had a sticky injector before (sticking closed or sticking open will both cause problems) and that whilst you may have lucked out in guessing which one(s) were sticking and replaced them, there may be a small imbalance now between the various injectors, probably between your originals and the replacements. (Especially if those replacements sat on a wrecked car for a long time without use) A small amount of imbalance is probably preferable to one that is outright sticking though!

Thinking back I'm wondering if I might have an injector that occasionally sticks open slightly - some time ago now I fitted a second hand fuel pressure regulator as the pressure from mine was a bit low (2.7 bars instead of 3.0) and the first time I got the fuel rail back together and put my fuel pressure gauge on the rail it would NOT hold the pressure when the pump wasn't running. It started dropping as soon as the pump was turned off and reached zero in about 20 seconds.

Normally a fuel rail should hold a steady pressure for at least 5-10 minutes with the engine off and pump stopped, and you can't do an injector balance test unless it can hold a steady pressure with the pump stopped.

As there was no fuel leaking anywhere the pressure drop could have only been either a sticking open injector, a leaky one way valve in the output of the fuel pump, or the fuel pressure regulator not closing properly. As I'd just fitted a second hand (but believed to be working properly) fuel pressure regulator I assumed that it was the regulator to blame and was about to take it out.

However after starting the engine and letting it run for a few minutes the pressure drop with the engine and fuel pump off disappeared completely. It was now holding its pressure perfectly for minutes. I checked it a couple more times that day and again a couple of times in later weeks and never saw it misbehave again.

Is it possible I was lucky enough to catch a stuck open injector red handed without realising what it was ? Or was it just a bit of grit stuck in the pressure regulator that got flushed away after a while ? I'll never know, but I'm now wondering if its an intermittent sticky injector that was caught in the act. If I'd been a bit quicker on the uptake I would have pinched the return hose to see if the leak was via the regulator or not but I didn't think of it at the time. If it was the injector I'm probably quite lucky I didn't hydro-lock a cylinder during my testing!

Yes I priced injector cleaning at around £90 for 6 injectors including postage, (assuming that all test ok after cleaning and none require replacing) so I'm strongly tempted to go ahead with that, especially after the results you got - I've already done or checked all the other things you've done, the injectors are the only remaining difference.

I'm thinking that I've either got an injector that intermittently sticks open or closed and/or there is enough of an imbalance in the flow rates (perhaps only intermittently) that one or more cylinders run too lean compared to the others - a cylinder running too lean will tend to misfire when the throttle is snapped, and also has more of a tendency to knock at a given timing advance than a normal cylinder.

So a single lean cylinder could cause early knocking and thus excessive timing retard without necessarily misfiring. Higher octane fuel will allow the lean running cylinder to operate with more timing advance (perhaps even full advance) without knocking thus disguises the lean running fault. For the first 6 months I owned the car I just used cheap 95 petrol and it performed great on that and I didn't notice a lot of difference on 99, now it needs 99 to run well and the loss in low rpm performance with lower octane is very obvious.

I've got the first week of March off work so I'm tempted to get the injectors out next weekend, get them sent away on the Monday, get them back by the following weekend and hopefully get them back in on the Saturday before my week off begins - that way if I run into any problems or the weather doesn't cooperate I have the following week to wait for a fine day or sort out any snags.

We don't need the car to get to work (most of our journey is by train and the station is a walk-able distance) and there are buses to get groceries etc. So I can make do without the car for a week or two at a pinch.

Very tempted...please keep me appraised of how well its running over the next week

[Mandrake]

I've just had a quick jaunt down that 70mph dual carriageway again, this time for some V-Power. Outbound @ 70mph, possibly with a bit of tail wind assistance = 45mpg. Same road coming back, definitely into the wind = 35-40mpg. The car felt a tiny bit less lively coming back home, but whether this is warm-start blues or the weather conditions (which have been horrendous today) I don't know. I still think the ECU needs to re-learn a lot, and this might just be a part of that.

If the engine characteristics have changed significantly (which replacing a faulty injector would do) it might be beneficial for you to do a full battery off reset - disconnect the battery for 10-15 minutes. This resets all mappings to default including the fuel trim and octane map/knock retard tables, so doing this after going from low octane to high octane fuel also helps it to learn more quickly that the fuel has changed.

Oh yeah, the extra vibration at tickover has now gone too.

It's getting there...

Nice. The vibration at tick over when you first started it may have just been because the ECU was applying previously learnt long term fuel trim before the oxygen sensor had time to warm up. Once the oxygen sensor was warmed up and the car was being used the fuel trim would gradually correct itself.

A battery off reset may have sped up the process. I find that mine tends to idle the smoothest after a cold start if I've done a battery off reset before hand - suggesting that the factory default map values are closer to correct for this engine than the ones that get learnt via the oxygen sensor.

Possibly either due to the oxygen sensor supplying inaccurate data when not properly warmed up, or an injector problem causing the ECU to attempt to compensate the mixture, saving this in the long term fuel trim. (On initial start up the long term fuel trim values are used while waiting for the oxygen sensor to warm up, rather than factory defaults - so if those long term fuel trims get skewed due to a sensor or running problem the skewed values will be in force at initial start up)

[Mandrake]

I have a suggestion. I don't know if it is feasible, but it could be worth examining. Is it possible to remove (dissolve) the old epoxy from a faulty coil pack, clean it up, and then re-epoxy the coil pack? As there is (at least) one faulty coil pack you wouldn't be any worse off if it didn't work.

EDIT; a bit of research has found that heating epoxy to around 100C turns it a bit rubbery and helps removal. This might be some useful info;

http://kevtris.org/Projects/votraxpss/unpot.html" onclick="window.open(this.href);return false;

Having rebuilt epoxy potted EHT multipliers a couple of times before (successfully I might add) I think the amount of work and small chance of 100% success would make it not worthwhile unless coil packs became unobtanium.

There is a fairly good chance that if there is an insulation breakdown that it could be between the primary and secondary windings, not between the secondary and the outside air. All visible external cracks were sealed on the outside with epoxy, all windings meter tested ok and measure identical to my two other coil packs, yet the car still ran like a pile of poo on it.

My conclusion (without doing a proper spark strength test) is that there is probably an internal insulation breakdown between the primary and secondary windings limiting maximum spark voltage. (probably on only one of the three coils in the pack) Since its a waste spark system such a break down in one coil would take out two oppositely timed cylinders. Not necessarily a huge vibration/imbalance, but a huge loss of power.

I'm assuming the secondary is wound on the outside of the primary (?) making it impossible to fix the insulation in between without rewinding the secondary. Not something I could be bothered attempting! (especially when I seem to have a good working one)

One day when I get some time on my hands I'll set up a test rig to measure the maximum spark voltage of the coils off the car. That's the only way we'll know for sure what the problem is, but I'll bet anything its low spark voltage from one of the coils, probably worse when the pack is hot from heat soak.

[stevieb]

Regarding your plugs, the centre electrodes do look past their best. I know that type of plug is supposed to have a sharp pointed tip on the centre electrode but it looks like it has eroded away to leave a considerably larger than normal gap. Did you measure the gap ? It's supposed to be exactly 1mm but it looks like a lot more than that to me. Compare that to the size of the gap of my plugs in the picture I posted.

Spark voltage is directly proportional to gap so if the gap is 50% wider than it should be it will take a 50% higher spark voltage under otherwise identical operating conditions! If the coil/leads can't supply a high enough voltage you'll get a misfire under those conditions where a high voltage is required.

Even if the coil can supply the additional voltage due to the larger gap and a misfire doesn't result the higher voltage will place additional dielectric stress on all the insulators in both the coil pack and the plug leads - causing them to potentially fail at a lower mileage than they otherwise would. A smaller correct spark plug gap keeps the voltage down to the range it should be.

So I'd definitely replace the spark plugs when convenient but if its running really well since the injectors were swapped its not urgent. Personally I like the dual electrode ones like those I pictured (and they are the OEM type after all, probably chosen for a reason) but that's just me. As you say a waste spark system will erode the electrodes at twice the normal rate, and the dual electrode plugs are primarily designed to double the life time of the plug by providing two potential gaps. (Only one gap sparks at a time but as that one wears down the other starts sparking and visa versa, so they wear evenly)

That all makes sense. I've been to the local Pug stealer (less than two minutes walk from home) and ordered a couple more inlet manifold gaskets. They due in on Wednesday, by which time I plan on having a set of six nice new plugs to install. I quite like these Denso ones, and might go for some of their newer equivalents.

These look an interesting alternative to the traditional dual electrode approach - http://www.eurocarparts.com/ecp/c/Peuge ... 356&000301" onclick="window.open(this.href);return false; - and a good price too.

On the injectors - glad to hear that they're not too difficult to replace! I didn't think they would be as I had the fuel rails half out when I swapped the fuel pressure regulator over. Is it difficult to completely remove them ? I think if I was sending the injectors away to be cleaned I would want to take the fuel rail right out and give it a good clean inside with carb cleaner.

Sounds like you were right that some of the ticking noise was the injectors! Mine is still silent when cold but there is a definite tick from two different sources when hot - I'm starting to wonder if that is a couple of rear injectors becoming noisy when hot...

I think the rear injectors are working in the most inclement part of the engine - that inlet manifold must hold an awful lot of extra heat in there. You could think that the front ones would be prone to it too, but I can't help but think those "scoops" in the plastic engine cover help the airflow around the front ones a bit. The rear ones don't have any airflow. I also noticed on mine that the plugs for the rear injectors had full rubber boots unlike the fronts which are regular, exposed, plugs. These rubber boots have scorch-marks on them and look like they'll be turning brittle very soon.

As for getting the injectors out of the rails, it's not too difficult. Mine were still slightly warm when I got to that stage, and a little bit of prising with a thin tip flat-blade got them out. The secondhand ones were a lot tighter when I took them out for safe-keeping last year - possibly because they were cold, possibly because they'd been sat idle for some length of time. There's a flange at the top of them that's a larger diameter than the hole in the rail - if you can get a good purchase under this, then they ease out nicely with a gentle twist of the screwdriver. This flange also tells you when they're pushed back home properly - if there's a gap then they're not home. One thing I didn't mention was that the upper, larger, o-rings on my front ones were split around the circumference. You know how sometimes O-rings have that seam that runs round the outer circumference? It was like that had opened up. As you may guess, I swapped these O-rings for healthier ones. As for cleaning out the fuel rails, the petrol that poured out of both connectors and down my arm as soon as I turned the rail over was lovely and clean and I would imagine took any lingering grit with it - so I elected to leave well alone. Had I been installing cleaned injectors I probably would've flushed the rails, as you say, but all I was concerned with was making the change and seeing what difference it made. I had this weekend free as a plan B if I needed to revert everything back to how it was before.

Your slightly lumpy idle may just be injector balance is not perfect - you've mixed some of your original injectors with some untested second hand ones, its quite possible that you had a sticky injector before (sticking closed or sticking open will both cause problems) and that whilst you may have lucked out in guessing which one(s) were sticking and replaced them, there may be a small imbalance now between the various injectors, probably between your originals and the replacements. (Especially if those replacements sat on a wrecked car for a long time without use) A small amount of imbalance is probably preferable to one that is outright sticking though!

Thinking back I'm wondering if I might have an injector that occasionally sticks open slightly - some time ago now I fitted a second hand fuel pressure regulator as the pressure from mine was a bit low (2.7 bars instead of 3.0) and the first time I got the fuel rail back together and put my fuel pressure gauge on the rail it would NOT hold the pressure when the pump wasn't running. It started dropping as soon as the pump was turned off and reached zero in about 20 seconds.

Normally a fuel rail should hold a steady pressure for at least 5-10 minutes with the engine off and pump stopped, and you can't do an injector balance test unless it can hold a steady pressure with the pump stopped.

As there was no fuel leaking anywhere the pressure drop could have only been either a sticking open injector, a leaky one way valve in the output of the fuel pump, or the fuel pressure regulator not closing properly. As I'd just fitted a second hand (but believed to be working properly) fuel pressure regulator I assumed that it was the regulator to blame and was about to take it out.

However after starting the engine and letting it run for a few minutes the pressure drop with the engine and fuel pump off disappeared completely. It was now holding its pressure perfectly for minutes. I checked it a couple more times that day and again a couple of times in later weeks and never saw it misbehave again.

Is it possible I was lucky enough to catch a stuck open injector red handed without realising what it was ? Or was it just a bit of grit stuck in the pressure regulator that got flushed away after a while ? I'll never know, but I'm now wondering if its an intermittent sticky injector that was caught in the act. If I'd been a bit quicker on the uptake I would have pinched the return hose to see if the leak was via the regulator or not but I didn't think of it at the time. If it was the injector I'm probably quite lucky I didn't hydro-lock a cylinder during my testing!

That's exactly what was happening in a video I saw on Youtube the other day - I wish I'd saved the link because I can't remember where it was now... It was almost enough for me to consider buying a fuel pressure gauge, but I reasoned that it would only tell me what I already knew, and swapping injectors wouldn't cost me anything as I had the spares. I think you are/were right about the imbalance, but the car was so much smoother today maybe the ECU is learning (or the replacement injectors are becoming less noisy/sticky). I may well do the reset though - or maybe hang it back 'til the plugs are done mid-week and get another HUGE improvement in performance and mpg

Yes I priced injector cleaning at around £90 for 6 injectors including postage, (assuming that all test ok after cleaning and none require replacing) so I'm strongly tempted to go ahead with that, especially after the results you got - I've already done or checked all the other things you've done, the injectors are the only remaining difference.

I'm thinking that I've either got an injector that intermittently sticks open or closed and/or there is enough of an imbalance in the flow rates (perhaps only intermittently) that one or more cylinders run too lean compared to the others - a cylinder running too lean will tend to misfire when the throttle is snapped, and also has more of a tendency to knock at a given timing advance than a normal cylinder.

So a single lean cylinder could cause early knocking and thus excessive timing retard without necessarily misfiring. Higher octane fuel will allow the lean running cylinder to operate with more timing advance (perhaps even full advance) without knocking thus disguises the lean running fault. For the first 6 months I owned the car I just used cheap 95 petrol and it performed great on that and I didn't notice a lot of difference on 99, now it needs 99 to run well and the loss in low rpm performance with lower octane is very obvious.

I've got the first week of March off work so I'm tempted to get the injectors out next weekend, get them sent away on the Monday, get them back by the following weekend and hopefully get them back in on the Saturday before my week off begins - that way if I run into any problems or the weather doesn't cooperate I have the following week to wait for a fine day or sort out any snags.

We don't need the car to get to work (most of our journey is by train and the station is a walk-able distance) and there are buses to get groceries etc. So I can make do without the car for a week or two at a pinch.

Very tempted...please keep me appraised of how well its running over the next week

I'd still be tempted to get hold of some spare injectors - like these http://www.ebay.co.uk/itm/Peugeot-406-3 ... 3389faef68 . If you take the car off the road you only need the specialist to find one of your injectors beyond repair or there be some other problem, and you'll be kicking yourself for not having spares. If you send off six spares and there's a duff one, then you can sacrifice your car for a week whilst one (or maybe two, just in case) of your originals is sent for treatment to make up the six. The other argument is if you get a cheap set that are still in their rails (as I did) then you can happily flush out the used rails whilst the injectors are away being treated, and assuming they all come back without any problems re-insert them into their original rails and just swap the complete sets over in your own time - that way the job is a lot less messy and time consuming. The added bonus is the option of re-selling your unwanted injectors on Ebay to reap some of the cost back.

The comment on cheap 95 octane fuel is interesting. Do you mean you used supermarket fuel, or just "cheap" when in context with high octane fuel? I ask because my previous 406 was the lovely 8-valve 2.0 litre petrol turbo (my favourite Peugeot engine, despite similar sensor issues - it was fab ), and it HATED supermarket fuel with a passion. I only used it twice out of necessity (I'd learnt the difference between supermarket and local Shell garage fuel many moons ago when I anally measured the tank-to-tank mpg of my first car - a 1.3 309). One occasion sticks in my mind when I put a tankful of Sainsbury's high octane stuff in at Swadlincote in Derbyshire. My drive home from there was 20% of mixed 30mph villages and 60mph country roads, followed by 80% of 70mph motorway spec road, and you could physically feel the car getting weaker and weaker. I seriously started to wonder where my RAC card was, it got so bad. I had the full-on "rubber throttle". The car got me home with a bigger drop in fuel than I was used to, and carried on running like cack for a few days until I filled up at the Shell near home. Instantly, with regular Shell fuel, it returned to normal. I don't know what it is about supermarket fuel, but it just isn't as good as the stuff from mainstream forecourts. And I think if it's causing these power and economy issues then what other problems might it be causing? I have little doubt my stuck injector is related to my car being two and a half years old before it left the forecourt - sitting there with a litre of cheap petrol going stale in its tank - and I wonder if the use of this cheaper petrol on a regular basis can have a similar effect over time. In my case, if the previous owner added to an existing problem with supermarket 95RON fuel, it's hardly surprising they've all finally come home to roost...

[Stempy]

Congratulations on reaching the magic 100 pages.

I think when you read the numerous horror stories of dodgy supermarket fuel with high silicon content etc it goes to show that they probably do as they do with all their other products and drive the buy price down and source their fuel from somewhere with perhaps less quality control as per the horse meat issue, so who knows what it been diluted or contaminated with?

I have a Shell garage very close by and always go there when possible. If you get one of the loyalty cards you can soon build up a stash of fuel vouchers to help off set the extra cost, plus you will get better mpg anyway and benefit from keeping your engine in good shape.

Supermarket fuel is cheap and convenient for those who just see their cars as a form of transport. Those that cherish their vehicles should know better.

[Hell Razor5543]

I have a Shell station 2 miles away from me. Since the problem with Tesco fuel, I have only ever used Shell in my personal car (and whatever I am allowed to use in the company van).