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

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Mandrake
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Post by Mandrake »

addo wrote:You could also replace the ground cable with new heavy gauge that's pre-terminated in an eye for the gearbox end.
Good idea, unlike the positive that has wires going to many locations including the fuse box the negative cable only has two wires, one to the plate right next to the battery and one to the gearbox, replacing the whole cable and terminal together with a new pre-crimped terminal and cable would be my preferred option, I'll have to measure the length from the terminal to the gearbox and see what's available in the way of negative terminals with two way cables.

I can easily shorten and re-terminate the end that's going to the body-shell earth plate if necessary, as long as the long one is about the right length. Anyone have any ideas on who might sell such cables complete with terminal already crimped ?

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Re: Xantia V6 broken exhaust (update: and rough low rpm runn

Post by Mandrake »

CitroJim wrote:Earth is to a bolt on the top of the gearbox. Bolt and crinkle washer...

Check the other main earth to the bodyshell on the plate on the NS Inner wing too...
The connection from the negative terminal to the bodyshell earth plate seems ok Jim, I wasn't able to measure any significant voltage drop there with the engine running, lights on etc, however I haven't checked the connection to the gearbox at the moment, and that's the one that matters as that will be the supply path to the ECU.

I really do think those two green earth wires from the harness that bolt onto the the top of the front inlet rocker cover are highly suspect and will be replacing the terminals ASAP however it's prudent of me to check the complete path including the connection at the gearbox...

I plan to check the grounds at the ECU connector with my scope before touching those green earth wires again, if I'm right there will be a load of switching hash on the ECU grounds relative to battery negative due to those green earth wires. It would be nice to get a conclusive before/after measurement of voltage drop/hash rather than just replace the terminals and wonder how long the fix might last... Fingers crossed. [-o<

Another thing I could really do with is a current clamp probe for my scope, being able to see the current waveforms for coil primaries, injectors etc without intrusively affecting the wiring would greatly help diagnose electrical problems but even the cheapest ones I can find are too expensive just to be used a few times to find one fault...

addo
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Post by addo »

Factors sell battery gauge cables with a crimped eye each end. You just buy the closest overlength and trim one end shorter.

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Re: Xantia V6 broken exhaust (update: and rough low rpm runn

Post by Mandrake »

That's not what I meant. I was hoping to buy a cable that already had the battery terminal crimped onto two cables, similar to the original... The cables with a crimped eye each end are readily available but I don't want an extra eye terminal at the battery terminal end if it can be avoided.

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Post by addo »

I don't know about that; most of the crimp type battery terminals are not the greatest. A commercial crimper is massive - like a pair of bolt cutters.

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Re: Xantia V6 broken exhaust (update: and rough low rpm runn

Post by Mandrake »

So I checked the ECU grounds today at the ECU connector and couldn't really find anything wrong - of the different ground pins on the ECU one showed about 33 millivolts relative to battery negative while idling, the others didn't show anything at all, which was a disappointment as I was hoping to see an obvious problem.

On the other hand when I drove into Glasgow and back late last night the car was in one of its "running well" moods, and was also running fairly well today on a second trip into Glasgow before commencing work on the car, so it wasn't really symptomatic at the time of the test...

I also found that the Lexia reading of battery voltage at the ECU isn't as accurate as I assumed. While the Lexia said 13.3 volts my multimeter back probing the ECU connector said 13.9 volts, compared to 14.2 volts at the battery terminals so the large voltage drop I was looking for doesn't exist. I think 0.3 volts total voltage drop including positive and earth returns is perfectly acceptable.

I went ahead and replaced the two earth terminals anyway. A couple of things I noticed in the process though, one is that the right hand most spark plug lead - the one that always gets pinched under the plastic cover no matter what you do, is rammed down hard on top of the right hand earth wire, and I was wondering whether there was any chance that a flash over might be occurring there... Does the right hand spark plug wire get crushed and kinked like this on other peoples V6's ?

Image

There doesn't seem to be any way to avoid it due to the shape of the vents on the plastic cover, and its no wonder they have the protective sleeve over the wire is there...

The other thing I noticed is that the same right hand earth terminal had a weird coating of carbon on the wire:

Image

Does anyone think this might be due to burning/arching of an intermittent joint ? Or could a (previous) faulty plug lead have been arcing across to the wire ? I just thought it looked odd when the other terminal showed no signs of the same carbon deposits.

Here are the nice newly crimped terminals, the right hand one I also slipped a layer of heat shrink over to give it a bit of extra protection just in case the plug lead was tempted to flash over to it:

Image
Image

And no doubt long time readers will be waiting for me to say that it seems to be fixed... and it does... but given that I have thought its been fixed so many times I'm not assuming anything until it has run for several weeks... but the performance of the engine has been excellent this afternoon, and what I also noticed is that there has been no "sag" in performance that usually occurs when the engine bay gets really heat soaked and stinking hot...

The gearbox was acting a bit like it was confused and didn't know what to do with this extra power so I did an autoadaptive reset on it - unlike last time I did a reset where it made things much worse and took a long time to recover, this time it made an almost immediate improvement, the gear changes became much quicker and sharper with the whole driving experience feeling much more positive and snappy.

So basically it seems to be running really well now, but I'm sure I've just jinxed it by saying so!! :twisted: I have a theory on why the gearbox gets confused when the engine isn't running properly which I've gone into some detail in Ben's grumbly gearbox thread:

http://www.frenchcarforum.co.uk/forum/v ... =3&t=45083" onclick="window.open(this.href);return false;

But essentially what it comes down to is that the torque figure that the engine ECU sends to the gearbox ECU is critical information that the gearbox uses when judging how much pressure to apply to clutches, how quickly and so on...but it is only an ESTIMATED figure based on theoretical engine performance, and a misbehaving engine that is for example misfiring will produce less torque than the ideal figure which it is telling the gearbox it is producing. Therefore the gearbox makes the wrong adjustments for clutch pressures etc for the amount of torque its actually receiving.

If the error was consistently wrong by the same amount the auto adaptive system would eventually learn to compensate, but if the torque error is randomly fluctuating as it would during an intermittent misfire that is coming and going, its over compensating one minute and under compensating the next, forever trying to adapt and forever getting it wrong!

It seems that the gearbox behaviour cannot be judged unless the engine is running 100% and has no performance issues, especially intermittent ones...

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Re: Xantia V6 broken exhaust (update: and rough low rpm runn

Post by Mandrake »

I knew it was too good to be true, another trip to Glasgow to pick someone up tonight and by the time I returned it was feeling "lethargic" and lacking in urge at low rpm with a slightly rubbery throttle response. :evil: Performance at higher rpm above about 3500 seemed normal. :roll:

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Post by addo »

The sootiness as shown on that earthing picture, seems common and I believe to be a feature of degrading plastic in a hostile environment (ie; solvent vapours, heat). There's negligible corrosion/oxidisation visible, which is a good sign.

I hope the replacement eye was well crimped; if you look at the cut cross-section of a professionally crimped connection it is usually squashed into a heartlike shape and there is SFA airspace visible. Many hand crimpers just mash the wire strands into a sort of dented oval.

July 7th is supposed to be sunny for you.

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Post by addo »

Sweet Firetruck All.

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Re:

Post by Mandrake »

addo wrote:The sootiness as shown on that earthing picture, seems common and I believe to be a feature of degrading plastic in a hostile environment (ie; solvent vapours, heat). There's negligible corrosion/oxidisation visible, which is a good sign.
I wonder whether the high electrostatic field around the spark plug leads helps attract soot or whether it contributes to the degradation in the earth wire insulation ? As there was no soot on the other terminal or any other wire for that matter.
I hope the replacement eye was well crimped; if you look at the cut cross-section of a professionally crimped connection it is usually squashed into a heartlike shape and there is SFA airspace visible. Many hand crimpers just mash the wire strands into a sort of dented oval.
Well the replacement terminals are not the two prong type like the originals that roll into a heart shape, its a butt joint crimp type eg just a round tube that gets squashed. I did use a double width ratchet crimper though, not one of the thin £5 manual ones with no ratchet, so its crimped as well as it could be. Seems to be a good tight fit with plenty of wire volume to fill the hole. (the wire only barely fitted into the hole before crimping)

Either way although it's good to have ruled it out the earth wires could just have been yet another in the long list of red herrings in the quest to find an intermittent fault! I certainly wasn't able to prove with measurements that they were faulty in any way. The Lexia ECU supply voltage reading after replacing them is identical to what it was before as well.

I've been thinking again about what was done yesterday apart from crimping the new terminals on. To measure the voltage on the ECU I had to remove the plug from the ECU and slip it out of its sheath to get at the back of the terminals - in the process the temporary memory (eg fuel trim and knock retard tables) will have been cleared, after crimping the new terminals I went for a test drive with the plastic top cover still off the engine and the back of the ECU plug still exposed - perfect performance, tons of zip, no hesitation at all.

I then put the top cover back on the engine, reassembled the ECU plug (once again disconnecting the ECU for a few minutes) and then went for a second test drive around the same "circuit" - again perfect performance with tons of zip and no mid journey sag or fall off in performance or responsiveness. I did these two separate tests just in case it was something to do with the top cover pressing on the spark plug leads etc.

I then let the car sit for several hours and went to pick someone up from Glasgow - it started off very zippy but within only a couple of minutes I started to notice the typical flattening out of performance and hesitation creeping back in, and by the time I'd done 10 miles it was feeling quite lethargic and lacking in oomph with "rubber accelerator pedal syndrome".

What's the connection if the terminals were placebo ? Possibly two related things - one is that before both trips where the performance was excellent the ECU had just been reset by being unplugged...

The second is that on both occasions the engine had been started and left to idle for over 5 minutes without being driven or even being revved up - I was busy measuring voltage drop between different terminals, observing the idle to see if it was smooth or missing, checking live data from the Lexia against my voltmeter etc.

On the third occasion where the performance rapidly deteriorated the car had just sat for several hours, was started, and then driven away about 10 seconds after starting. I have noticed this apparent connection many times before - if the car has sat for a long time and I start it then drive away quickly chances are good that performance will be poor, immediately or relatively quickly and remain that way for the rest of the journey.

If the car has been left to idle for a good few minutes before being driven performance is usually much better. It occurs to me that any time I'm doing work on this car chasing the problem of course the car will sit idling for a few minutes while I'm checking things. Therefore its a self fulfilling prophecy - the car is left to idle for a while while/after doing work on it, it performs better, I think its fixed, when it goes back to regular use where it is started and then driven off quickly it misbehaves.

In an attempt to confirm that its driving/revving the engine while cold that causes the problem today when going out I let it idle for about 2-3 minutes before driving off, then for the first mile of the journey I tried to drive slowly and keep the revs below 2000 by manually upshifting (snow mode 1-2-3) until it had started to warm up, after dropping off the passengers I gave it a bit of a thrash on its usual circuit and for the first 5 minutes it was going like a complete rocket again just like it was after replacing the terminals. Bingo! It's not the work I'm doing to the engine its the changing conditions under which it's being started, warmed up, revved, and driven.

Long story short I think we're back to the knock sensor activity retard theory again, where either non-knock engine noise is triggering a properly working knock sensor (noisy tappets or other mechanical noise besides knocking) or a problem with the knock sensor itself or wiring. (I've even read of cases where a knock sensor bolt has come loose causing the knock sensor to rattle on its mounting)

A couple of the tappets are still quite noisy despite the engine oil change, is there any possibility that the oil pressure is low, or is low for the first few minutes then comes right ? Could it be that if the car is driven quickly after starting and revved the oil pressure is a bit low making the engine a bit nosier setting off the knock sensor ?

Resetting the ECU clears the knock table giving it a fresh start, however perhaps if the engine is revved under load when cold the knock sensor picks up noise that the ECU thinks is knock, the ECU then starts filling in retard values in the appropriate RPM/Load cell in its table. With real knock the knock will go away when some retard is applied but if its just mechanical noise the "'knock" will not respond to the retard and not go away causing the ECU to progressively retard the timing of that cell to the maximum allowable amount, which from my reading is typically between 6-10 degrees on most ECU's but can be as high as 20 degrees on some systems. (There's no information that I can find for the ES9J4 unfortunately)

Depending on the throttle/load combinations that you drive the engine through when its cold and "noisy" you end up with seemingly random cells in the knock retard table filled in with large negative values and other cells that are untouched hence flat spots, hesitation and severe lack of power, but only at particular rpm/load combinations. It certainly feels like retarded timing, and it does feel like there are certain rpm/load combinations where its severely retarded and bogging, and others where it feels quite normal.

So what do I do guys ? I guess the first step is I have to prove conclusively that knock sensor activity is indeed retarding the timing when it shouldn't. The problem is I don't believe the knock retard is separated out on the Lexia display - I though it was included in the "torque reduction" figure but now I'm pretty sure its not. I believe that figure is reserved for "deliberate" torque reductions, eg the gearbox requesting torque reduction during a gear change, and I also think its used for timing controlled (fine) idle speed trimming, with the knock table related retard being built into the base advance figure. :( That means there's no real way for me to see it on the Lexia because the base advance will change under different conditions and I don't know what it should be in the first place. So monitoring it with the Lexia is out.

I think the only way to prove this is to turn down the sensitivity of the knock sensor a bit with some resistors and see whether the power loss, flat spots and hesitation go away. I'm probably safe to do this while running on 99 octane and I would only reduce it a small amount anyway.

Assuming this does identify the knock sensor signal as the culprit, finding what's actually causing it could be difficulty. Low oil pressure ? Faulty hydraulic tappets ? Other engine wear noises ? Loose or over tightened knock sensor ? Broken knock sensor ? Broken wire from the connector to the knock sensor ? (I've already confirmed the harness side wiring is ok) There are a dozen different things mechanical and electrical that could cause false knock triggering...

I WILL beat this thing! :twisted: Or at least find what the problem is...

PS I think the new coil pack did genuinely die on me in the last month, the symptoms of that were very different than those I'm still chasing which have been there intermittently for months, I think the coil pack was just an annoying distraction that sidetracked me from the real problem.

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Post by addo »

It could even be off-gassing from the plug lead covers that sooted up your earthing eye.

Re the crimps, if you pull apart a new terminal there is a metal sleeve (as you saw) over a split, rolled-up band. Often the outer sleeve is thin and remains with the plastic slipover part. I usually discard this bit, crimp hard and use doublewall heatshrink over it - sometimes with solder added into the mix.

I'm not convinced a sensor is at fault. It's possible that stuff is getting scrambled inside the ECU - see my posts last year about drying up caps, but observation is that most are very nice inside when you look so the degradation scenario is going to be slow and uncommon. Can you not fully test the cat by substitution with a gutted one (maybe Paul has one to spare)? That would allow for extensive road testing, which you've applied to most other possibles.

If it makes you feel any better my own car is running rough - but I suspect it's the head gasket starting to go between cylinders... No overtemp issues, no smoke, no loss of water, no stumbles - plenty of grunt but maybe 10% down on where it could be. Lost a traffic light drag to a bike today, and I usually don't.

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Re:

Post by Mandrake »

addo wrote:It could even be off-gassing from the plug lead covers that sooted up your earthing eye.

Re the crimps, if you pull apart a new terminal there is a metal sleeve (as you saw) over a split, rolled-up band. Often the outer sleeve is thin and remains with the plastic slipover part. I usually discard this bit, crimp hard and use doublewall heatshrink over it - sometimes with solder added into the mix.
Shhhhh, don't let Jim hear you would solder the joint as well... :twisted:

It does get pretty hot there but I think people overestimate how "fragile" good soldered joints are...and over estimate the reliability of crimped joints, no matter how well done...

You're right, upon closer inspection there is a split at the top of the tube, I hadn't noticed. The crimper I have is for butt joints though so doesn't have the necessary jaws to crimp into a heart shape, and wouldn't fit the terminal properly without the plastic sleeve. I do have a crimper designed for two prong terminals too but its just a cheap thin one for small terminals and wouldn't do a good job of that size terminal.

In any case I'm pretty sure the terminals old or new are not at fault so I'm not going to expend any more energy on them just at the moment.
I'm not convinced a sensor is at fault. It's possible that stuff is getting scrambled inside the ECU - see my posts last year about drying up caps, but observation is that most are very nice inside when you look so the degradation scenario is going to be slow and uncommon.
I'm not convinced that the knock sensor itself is faulty either, just that a knock signal as received at the ECU possibly a "false knock" signal is the cause of the intermittent power loss and hesitation...

I'll tell you another thing that fingers the knock signal - when I did test the car with the knock sensor unplugged some while ago (only for 10 minutes mind you) two things happened - one is that the performance dropped dramatically, so much so that the engine lost its throaty engine note and sounded more like a kitten than a big cat... :twisted:

The reason being that the ECU detected and logged a faulty knock sensor and then applies a permanent timing retard to the entire timing map for safety, I don't know how much, but probably around 6-10 degrees based on other systems.

The second thing that happened is the constantly varying performance, hesitation on pickup and all the other symptoms went away - the car was flat feeling but extremely smooth with no intermittent hesitation on pickup, random large fluctuations in performance or throttle lag.

I might unplug the sensor and test it over a longer test drive to see if the performance is consistent (albeit flat) this time as well. I really do think the constant variations in performance I'm seeing and even the throttle lag are timing related. When there is throttle lag you can actually hear the engine gradually "come on song" over a good half a second or more, whereas when its not lagging the engine note is instant with throttle. Retarded timing causes a loss of engine note, I've already proven that with the sensor unplugged. (It can also be heard as a loss of engine note during an upshift when accelerating hard when the gearbox commands retarded timing, you get half a second of almost completely muted engine note despite keeping the throttle down...)

I'm pretty sure about the knock signal being the problem, but I'm not sure at all what the exact source of the problem is. I still have a couple of pretty noisy tappets that the oil change didn't do anything for, in fact if anything with the new oil they're noisier and don't quiet as quickly on startup as they did with the old oil plus additive. Since its easy to do I'm going to try the lubegard engine additive to see if it is able to quiet or unstick the remaining noisy hydraulic lifters any further. I used the wynns one last time and it did seem to work but I get the impression the wynns one is more of a quick fix that you don't want to leave in permanently, so I'll give the lubegard one a try this time after the success with their gearbox additive.

By the way can anyone tell me an easy way to drain half a litre of engine oil out ? Its right near the top mark without enough room to add any additive. After the debacle where I lost half the gearbox oil onto the ground and burnt my fingers while trying to drain 300mL I'm reluctant to try to do a partial drain through the sump plug.

Is it possible to suck it out and syphon through the dipstick with a hose perhaps ?
Can you not fully test the cat by substitution with a gutted one (maybe Paul has one to spare)? That would allow for extensive road testing, which you've applied to most other possibles.
You really need to give up on the cat... :lol: hand to heart, its not the cat, and in no way could it match the symptoms. For starters there is no loss of performance above 4000 rpm. Although I had performance loss above 4000 with the coil pack playing up I'm not seeing any now. If I put my foot down in sport mode above 4000 rpm it pulls like a train, which wouldn't be possible with a restricted exhaust.

Really, its not the exhaust...and there's no way I'd be playing with gutting it when I have an MOT in less than a month...
If it makes you feel any better my own car is running rough - but I suspect it's the head gasket starting to go between cylinders... No overtemp issues, no smoke, no loss of water, no stumbles - plenty of grunt but maybe 10% down on where it could be. Lost a traffic light drag to a bike today, and I usually don't.
No it doesn't make me feel better.... I found a post from myself in 2007 complaining about my old Xantia (2 litre 8 valve petrol auto) being about 20% down on power - I had forgotten about that, most of the time it never went as well as my Dad's Xantia with the same engine and gearbox, I never did get to the bottom of that, and every now and then it would jump back to full performance for a couple of days then go a bit flat again...

In those days I had no Lexia and little if any understanding of performance troubleshooting, knowing what I know now and having a Lexia I'm sure I could have found that problem...

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Post by addo »

Your age of V6 is probably a little too old for the dipstick siphoning.

I'll leave the exhaust issues when I see a dyno chart.

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Re: Xantia V6 broken exhaust (update: and rough low rpm runn

Post by Mandrake »

Just found this in the ES9J4 technical data:
5.3. Engine oil change
The engine oil must be changed with the engine hot just after switching off the engine. It is possible to drain the engines via a suction device. The end of the dipstick guide tube has been enlarged, which enables a tube to be connected to a suction draining device.
N.B. : It is still possible to drain the engines by removing the oil sump drain plug.
So it looks like the dipstick is designed for oil removal by suction. Whether it would take continuous suction or whether syphoning would be possible I don't know though...

What would you be expecting to see on a dyno chart for a blocked exhaust though ? All its going to tell you is how much torque you have at each RPM and how much it falls short of what it should be... it doesn't really pinpoint the cause...

addo
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Post by addo »

Have you seen the suction pumps? They're all over Fleabay now, but about $120 here from memory. I've avoided buying one thus far. A benefit of them, is they're graduated in litres so you can see how much is removed.

http://www.ebay.co.uk/itm/400435661457" onclick="window.open(this.href);return false;

An experienced dyno operator will have a gut sense of what power an engine should put out; I've noticed from experience that if something bends their head a bit they'll often play with it for a while at no extra cost just to attempt understanding of an odd result. Also as the rollers really load up the car it brings gas flow problems (in or out) to a head.