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

[Mandrake]

Right, looks like the misfire is back again.

Not quite as bad as before, yet, but very similar symptoms. In particular I can notice the uneven engine beat when first starting the engine from cold while the idle speed settles down, and a significant loss of power and rougher / noisier running of the engine especially under load. (It was very smooth and quiet when running properly, and pulled MUCH better at low RPM than it is now)

The intermittent "throttle lag" I think is nothing more sinister than an intermittent misfire on one cylinder which as well as causing a direct loss of 1/6th of the power is causing the oxygen sensor to read false lean which then causes the ECU to richen the mixture (causing all the other cylinders to run far too rich) and back off the timing. So when you initially put your foot down it misfires and backs off the timing, then as the engine picks up a bit and the combustion pressures drop slightly the misfire goes away, the oxygen sensor reading returns to normal so the ECU restores the normal mixture and timing. The problem can literally come and go in periods of time as short as a minute or so - snappy and responsive one minute, laggy the next, ok again a few minutes later depending on driving conditions.

Looks like my temporary fix of rubber tape didn't last long. I might try re-applying some new tape and try two layers thick this time as well as doing all three leads in the bracket near the coil pack, assuming this once again temporarily restores normal running I think the only real solution is to replace the spark plug lead cartridge again...

[CitroJim]

Simon, were those new plug leads you got genuine ones or pattern ones?

I'm thinking it might be a good idea to dig deep and get some genuine ones perhaps...

[Mandrake]

As far as I know Jim, the one I bought is genuine OEM, it certainly looks the part with the same OEM brand stamped on it. (Can't recall what it is, Sagem I think)

I don't think its poor quality, the problem is I punctured the insulation near the coil pack end on the sharp edges of the black plastic cable guide. With 60,000+ volts and a nearby metal surface for it to flash over to you can't have even a tiny pinhole without a flashover and misfire.

All I did between it running like crap and running like a dream when I drove to David's and back was to tape up that one visible hole in the insulation...(well I did also measure the fuel rail pressure and purge the fuel rail pressure a few times in the process, but I really can't see how that could have any lasting effect when there was no measured problem with the fuel pressure in the first place)

I'm sure its just the insulation given way again, I only applied one thin layer and it gets very hot in the area above the coil pack, a bit too hot for rubber tape to last I think. I'm sure another set of leads from the same source will be ok and fix the problem for good.

[CitroJim]

Excellent It was just an early morning thought Simon...

How much are a set of leads now?

[Mandrake]

Excellent It was just an early morning thought Simon...

How much are a set of leads now?

These are the ones I got last time, they still seem to be the same price and in stock:

http://www.mister-auto.co.uk/en/ignitio ... _g685.html" onclick="window.open(this.href);return false;

After their 35% discount code is applied its around £45 shipped.

Buying them and fitting them is not the problem, its finding the chance to do it in winter weather without shelter as its a manifold off job.... I'm hoping a bit more thorough taping will last me through to spring...

[Ben82]

How are you finding Mister-Auto Simon? I've heard a lot of bad things from the UK side (wrong parts being shipped, bad customer service etc), but in Scandinavia they seem to be really highly rated (probably due to the huge savings over the monopolised mekonomen/meca pricing here). I've had no problems with them at all either (pretty quick to deliver, and they processed a return without issue).

[addo]

I'm finding them inaccessible (Désolé, livraison sur Australie n'est pas possible...)

To the matter otherwise discussed, it would be good for our poster to know what a dropped spark actually sounds/drives like. Perhaps this can be simulated on someone else's ES9J4 to have a test drive of and listen to?

I remain quite confident the cat is blocked; that said the 307 with duff Magnetti Marelli ECU (a first for my exposure) has opened my eyes to degraded control systems.

[lexi]

It is a pity the lead is out of sight..........or is it?. Head in there on a dark night,would see the glow worm of a short. Heat two layers of shrink tube on it. I have very heavy stuff here mate with the glue in it........rather stiff mind.

Mister Auto supplied my Vel Satis shocks. Exact same as originals.......... KYB. Came quickly and I traced the parcel from KYB in France. 90 quid delivered.......200 from Stealer.

[Mandrake]

Ben:

The spark plug leads are the only thing I've ordered from mister auto - there are not many places selling leads for the ES9J4 and of those their price was by far the best. From what I remember they took about a week to arrive and seem to be OEM. (At least they're the same brand as the ones that were on the car that looked very old)

Addo:

I know you're confident its a blocked exhaust but I really don't think it is. If you'd seen the night and day difference in performance from just taping up one ignition wire I think you'd agree. It was literally running better than it ever has since I've had the car. Because of the feedback loop with the oxygen sensor a misfire on even one cylinder drags the performance right down as the ECU gets confused by the high oxygen reading. That's why the car was performing a lot better with the oxygen sensor disconnected when the misfire was there...without the misfire performance was no worse with the oxygen sensor connected, maybe slightly better.

Even just above idle I'm noticing an irregular beat again which can't be caused by the exhaust. A blocked exhaust is going to cause restriction at high rpm but there has never been any symptoms at high RPM, it's always been at low RPM where a missing power pulse is going to be much more noticeable.

Also bear in mind its not a complete loss of spark to one cylinder like a faulty coil, depending on the gap between the broken insulation and the chassis the spark will only jump there and misfire at higher cylinder pressures where higher spark voltages are needed and normally developed. Under light driving it won't always misfire which means the misfire is coming and going during throttle and engine load variations, confusing the heck out of the ECU as the oxygen reading keeps swinging wildly between normal and lean with the ECU trying to compensate. Thus the intermittent nature of the problem.

Trust me, the performance problems were 100% fixed the instant I taped up the hole in the lead, it went like a rocket ship for a few hundred miles and then gradually deteriorated again to a now obvious misfire, which I'm fairly sure is just going to be my insulation tape bodge job failing due to heat. (I haven't taken the top cover off yet to look due to weather and other commitments but hope to this weekend)

I do now have a pressure gauge suitable for testing the back pressure in front of the cat though, so rest assured that will get tested at some point in the next few months for my own peace of mind, all I need is an adapter for the oxygen sensor socket with a long heat resistant fly lead to connect to my pressure gauge. That will then settle the blocked exhaust theory once and for all.

lexi:

The lead is nominally out of sight, but I only have to take the top plastic cover off (4 bolts) to expose the coil pack and my repair is right there in plain view. Looking for a spark in the dark is a good idea, only trouble is finding somewhere completely dark... There is a street lamp in our car park near the car and so much light pollution elsewhere I'd have to drive miles out onto a deserted country road in the middle of the night to find somewhere truly dark.

Not sure how it would be possible to repair with heat-shrink as there is no way to slide some over the connector at the end...also there is no spare length of cable so it has to follow the original routing exactly to reach. Even with one layer of rubber tape it was difficult to get it back into the plastic guide. Another question is what the voltage rating and leakage of heat shrink is - can it handle 60,000-70,000 volts with very low leakage even in damp conditions ? I'm not sure that it will.

Moisture related leakage at those voltages is going to make the spark weak even if it doesn't flash over to the chassis... given the previous correlation between the car running poorly in damp conditions and well in dry conditions (which I mentioned many times over the last few months) I would say that leakage was a major factor in the day to day variations in running with changes in weather. It's an interesting fact that the day I drove to David's was a VERY wet damp day with lots of rain yet it ran perfectly in conditions where it would have previously run like a dog. I think there's no doubt that a problem with the insulation is the major, perhaps only issue.

[CitroJim]

They're Boogiecords according to the advert and therefore OEM...

If damaged then sadly they're just about irreparable. Whatever you do won't be a lasting job unfortunately unless you can replace the cable completely.

[Mandrake]

Yes you're right Jim the new ones I fitted were Bougicord (I couldn't remember the name until I checked the website) and so were the originals that I removed that were very old and tatty, probably the originals...

I agree, I think the only permanent repair is to replace them again and not damage them this time! The environment is too harsh for a satisfactory patch up job when heat is considered as well as the high voltages. 60,000+ volts is funny stuff and the slightest bit of leakage or exposure to the air through a puncture in the insulation will cause havoc.

Most likely the rubber tape has flashed over and started tracking, leaving a tiny trail of conductive carbon on its surface...so while it may look ok to the eye it will no longer be sound thus the problem has returned. I'm surprised it lasted as long as it did to be honest, it was only a quick test to go for a test drive that continued to work for hundreds of miles! I think it proved the point though as I wouldn't have replaced the plug leads a second time on only a hunch without some evidence of improvement so I may have never got to the bottom of it otherwise...

[lexi]

You may not jump the full voltage on a small short though? This stuff is thick and tough man with glue inside but only 10mm dia and only temp repair anyway.

Be careful in looking for a dark spot you do not end up in any of those dogging sites. If you have your head under the bonnet in any of those places you could get a shock...........and it wont be 60,000 volts

The good thing is mate...........you ain't been stranded with it yet. See how your new leads go.

[Mandrake]

Some excellent news

After the renewed speculation about whether the ignition lead was really the whole problem or not, what could be causing throttle lag, whether the exhaust could still be blocked etc, I can confirm again that it's definitely the ignition lead that was the problem as I have again temporarily fixed it.

I took a few pictures this time to show what has been happening as a picture says a thousand words. I was pretty sure that my repair must have failed but I wasn't quite expecting this:

A hole has been melted right through the rubber where the hole in the cable is. The rubber looks like it has been hot all over, enough to soften it but it looks like the insulation broke down at the hole in the cable and that the continuous arcing through an initial small pinhole has melted a larger hole, thus the misfire returned...

Here is a picture of the original hole in the cable with the rubber tape removed:

That's all that has been causing the engine to run so badly for the last few months...

Here's my 2nd attempt at a more sturdy bodge job until I get the time and weather to fit new spark plug leads:

Three layers thick this time, and instead of trying to refit it in the guide (impossible with the extra thickness anyway) and risk tearing a hole in it I've just sat it above the guide with some tape around the three at the top to help keep it in place. An advantage to this is its now twice as far from the camshaft cover so less chance of arcing over to ground, (less dielectric stress on the insulation as well) and the top plastic cover presses down onto it slightly holding it in place. I noticed another small nick near the top end of the cable so I've taped that as well this time.

I don't know how long this bodge will last but in the mean time the performance is back to 100% again.

The changes in symptoms are: (that might help anyone else with a similar problem)

1) With the misfire the engine would vibrate/rock quite noticeably on its axis especially if you brought it up to 1500-2000rpm or so, now its absolutely steady with no visible vibration at any rpm. This is probably the best test for identifying an intermittent misfire IMO.

2) Power is dramatically better at all RPM but particularly at low RPM. With the misfire it was really struggling to pull below 2000rpm, all noise but no power, with the problem fixed it pulls freely and smoothly at low RPM, it has a kind of light and effortless feeling now.

3) As well as being smoother the engine is MUCH quieter under load. It was getting quite noisy over the last couple of weeks especially trying to pull at the low end making me wonder if something else was wrong too but no, as soon as the misfire was fixed its quiet again and power delivery is silky smooth.

4) The intermittent throttle lag is gone now too, the throttle is nice and responsive again. I still believe that the source of the throttle lag was the false lean reading from the oxygen sensor (due to one cylinder worth of unburnt oxygen) upsetting the ECU causing it to retard the timing as well as muck up the overall mixture. Because the misfire would come and go with load variations, so too would the ECU's adjustments to the timing.

So as far as I'm concerned its case closed. As soon as the weather picks up a bit I'll order new leads and fit them.

[CitroJim]

That's quite staggering Simon, how what appears to be an innocent enough injury can cause such grief..

One to bear in mind always when looking at odd running problems on a V6...

I'm really happy this thread has now reached a good and successful conclusion

[Mandrake]

Me too Jim.

I feel a bit of an idiot for being careless when fitting the wires in the first place but mistakes happen especially when you're in a hurry, and I've learnt the hard way what the symptoms are of this problem are. It's not something I'll fall for again...

An interesting thing is the gearbox is much happier now too - it definitely changes the behaviour of the gearbox in a number of ways... the downshifting when applying throttle is a lot more eager. For reasons I don't understand, when its misfiring and down on power at low rpm the gearbox is reluctant to change down a gear with increased throttle (other than a full kickdown) and will just let the engine labour away unable to make any headway, which I've complained about numerous times through the thread.

With the problem fixed it's happy to kick down with modest amounts of throttle when you're trying to move along. It must be something to do with the calculated engine load figures being messed up by the poorly running engine - we know that the gearbox does use the calculated load and torque figures supplied by the engine ECU as part of the decision making process for gear changing, so if those figures are wrong it makes sense the gearbox would behave strangely...

Another thing I had noticed again in the last few weeks was what I thought might have been the torque converter clutch shuddering slightly - trying to pull very slowly up a rise at low revs when navigating residential streets there was a slight worrying shudder, that seems to have gone now too, I'm guessing that the gearbox and the lockup clutch in particular don't like the lumpy torque of a misfiring engine at low rpm... now the power delivery from the engine is smooth even at low rpm the shudder seems to be gone...(or maybe it was the engine shuddering slightly on the engine mounts, either way its gone)

So your advice from a few hundred posts ago that the gearbox will misbehave if the engine isn't running properly is definitely confirmed! The gearbox is indeed very sensitive to the engine running smoothly and correctly and supplying it the correct data via the ECU interconnect...