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

[Mandrake]

If you are certain it's the coils, I would suggest you "break" a coil pack, and mount the coils remotely, with flying leads to all plugs - not crimped into a channel.

No I'm saying that although swapping the coil pack has again fixed the problem, (probably temporarily) that I don't think any of the coil packs are faulty, only that swapping them physically disturbs the actual fault which I think (but haven't proved yet) is the HT leads.

[Mandrake]

should I investigate the wiring where it runs under the cover a bit more closely first ?

This first.^^^

Pinch the leads back in and try to replicate the suspected short.......Make and break looking carefully what you are moving. I know I have mentioned it before but darkness is your friend for those shorts.

With so much light pollution around these parts I can't actually think of anywhere pitch black that I could stop and safely check under the bonnet in the middle of the night without either being mugged or having passers by stopping to see if I've broken down...

Were they nice Bougicord leads? Could be a bruised lead......maybe.

Yep they're Bougicord leads, from mister-auto.co.uk.

Have you tried pulling a plug lead when issues arise>? Not easy I know but could give indication if one makes a difference,or not

It mainly only happens under load so I'd have to check it under load somehow. As its a waste spark system pulling one of the leads would kill two cylinders, but you can slip a paper clip under each plug lead boot at the top of the coil and then earth one to kill the spark to a rear cylinder without upsetting the matching front cylinder.

The other thing I was thinking if it plays up again is to leave the top plastic cover off the engine for a while and lift the plug wires away from where I suspect they're arcing to earth by the earth wire lug and tape them with some 3m tape to give a bit of extra insulation. If that helps it might show that an arc is actually occurring through an insulation failure.

Apart from the kink in the wire I haven't noticed an obvious problem, but I need to give the wires a close visual inspection. (That's not always conclusive though as high voltage can flash over through the tiniest little pinhole that you can barely see visually)

[addo]

It's clearly a flawed design; they had four cracks at it; uprating the original coil specs, then going to COP, then revising the COP specs. Getting the coils off a vibrating motor and routing the leads in the least stressed manner, is standard practice for high performance engines.

[Mandrake]

It's clearly a flawed design; they had four cracks at it; uprating the original coil specs, then going to COP, then revising the COP specs. Getting the coils off a vibrating motor and routing the leads in the least stressed manner, is standard practice for high performance engines.

There are certainly some flaws in the coil pack approach on this engine... Although vibration from having the coil mounted directly on the engine is possibly a factor, I think the biggest flaw is the temperature that it must withstand, and in particular the constant temperature cycling between ambient and 100 degrees.

It's not just mounted on top of the engine, it's bolted metal to metal between the head and the transformer cores in the pack, so there is direct thermal conduction of heat into the coil units. The metal cores of the one I removed which had only been driven for 15 minutes were too hot to touch.

Making insulation that can withstand both the high voltages and the harsh environment that the coil pack is mounted in particularly the temperature cycling is a real challenge. My original coil pack is covered in massive cracks in the outer black housing, whether those housing cracks are important or not depend on whether there are cracks in the potting mix behind it, which can't be seen...

The one I got from KP is in a lot better condition but has a crack in the top of the potting mix in the narrow section between two coils, which may or may not be a problem... Even the brand new one that I fitted last year after only 9 months of service has quite a number of small cracks in the outer black housing...

As rugged as the coil pack looks it seems like its not up to the job of withstanding the harsh environment without developing cracks which potentially lead to insulation failure.

The poor wire routing is another problem - particularly the right hand most wire that comes from the cylinder 1 coil and goes to cylinder 5 at the rear.

At a glance the wire routing looks neat and tidy but that right hand wire goes right past the oil filler so any oil spilled at the oil filter runs down this wire to the connector, also where it routes out past the top of the plastic cover it goes directly under one of the "vent" holes in the cover whose curved shape digs down into the wire crushing it against the earth lug if the top two cover screws are done up properly.

They obviously know this is a problem area as some conduit trunking is fitted over the wire at this point but its not enough to protect it from being crushed and kinked - the original was badly kinked here and now so too is the replacement. It's not just mechanical damage like kinking and chaffing to worry about here - having an earth terminal more or less mashed up hard against the outside of the wire puts a lot of unnecessary dielectric stress on the insulation and can hasten its breakdown compared to if it had been suspended further out in space, with the effects of breakdown on engine running being far more severe with a close by earth for the spark to jump to. (Maximum spark voltage will be limited to the remaining free air gap, which is only about 3000v/mm)

Another problem with the routing is the fact that there is no slack whatsoever across the entire run, if there was a bit of slack available that wire could have been safely routed to one side. Another tight bend is where the wires come out of the cassette at the rear and do a sharp right angled bend to reach the back of the plastic guide - my original leads failed at this point, broken internally.

The waste spark system with three piece moulded coil pack presents major challenges for troubleshooting misfires too.

With conventional leads or a coil over plug system you can do a single cylinder drop test to identify a misfiring cylinder by simply lifting the lead or coil out - not possible for front cylinders on this engine because you can't lift one coil at a time. You would have lift the entire pack out and run extension leads to the three front coils to be able to do this, but if the root cause of the misfire was something like insulation breakdown or carbon tracking on one of the front boots the symptoms may go away when you move everything around - disturbing the other two front cylinders invalidates the test.

Because the coils are moulded in a pack of three you also can't swap them around to find if a misfire moves with the coil or stays with the cylinder... And then there is the not insignificant fact that if a coil is faulty you have to pay to replace all three. So yes, there are a number of flaws in the design and aspects of the design that make troubleshooting misfires very difficult.

I'm curious what you're referring to when you say they updated the original coils ? COP didn't come in until the ES9J4S, are you saying that there were two versions of the coil in the ES9J4 ?

[addo]

Yes, they superseded the original spec after a couple of years - I don't see a change of part number from 5970.A1 (there is a listing elsewhere for 5970.57), but from memory the maker changed.

If you can get your mitts on an Alfa Twin Spark coil, it might do to compare them - they're individual coils of a waste spark type. I have bought them for $150/set (four) used before.

[lexi]

There are many of these engines that don't have problems though? You can check ohm reading of coil pack, but tells you little of load reading.

So is it a scope on it while driving and that is why you need a probe? Keep "plugging" away

[Mandrake]

There are many of these engines that don't have problems though?

Sure, I'm perhaps overstating the issue because they do seem to be very reliable engines in general from everything I've read, (it's hard to find many postings about problems with these engines on the 'net) but they do still have a few known weak spots, like the cam box covers leaking oil into the spark plug wells etc.

You can check ohm reading of coil pack, but tells you little of load reading.

Yeah, all three coil packs of mine measure fine with an ohm meter - 0.5 ohms for the primaries and 12.4 k ohms for the secondary.

It doesn't tell you much though because the normal failure modes would be either a crack in the epoxy potting causing a high voltage flash over to ground (and therefore lost spark at the plug gap, potentially only happening under load when higher spark voltage is required) or a shorted turn, which won't cause an easy to measure change in the resistance.

A primary shorted turn (which might only manifest when hot) would show up clearly on a primary current waveform, a shorted turn on the secondary would possibly show up in the secondary voltage waveform, as would a flash over to earth, although if the insulation breakdown was on one of the front cylinder outputs it would be difficult to measure due to needing to lift the coil pack out etc...

So is it a scope on it while driving and that is why you need a probe? Keep "plugging" away

I think I might hold off on the current probe for the moment if I've narrowed the fault down to plug leads (a current clamp is twice the price of a set of leads) - I'll observe over the next few days, if any symptoms come back I'll take the top plastic cover off and leave it off, and tape up the leads at the suspect points, if that helps I think I'll just get some leads...

[Stempy]

There are many of these engines that don't have problems though? You can check ohm reading of coil pack, but tells you little of load reading.

So is it a scope on it while driving and that is why you need a probe? Keep "plugging" away

The coil pack on my Xantia had a big crack in it across the middle but it never caused any problems that I was aware of. Eventually I filled it with epoxy.

[Mandrake]

There are many of these engines that don't have problems though? You can check ohm reading of coil pack, but tells you little of load reading.

So is it a scope on it while driving and that is why you need a probe? Keep "plugging" away

The coil pack on my Xantia had a big crack in it across the middle but it never caused any problems that I was aware of. Eventually I filled it with epoxy.

It all depends on where the crack is doesn't it, whether it goes deep enough to expose any of the windings, and whether there is a convenient earth for the spark to jump through to. (Although even if there isn't, humidity on damp days will reduce the spark voltage if the crack exposes the winding...)

I thought about some epoxy resign to seal the crack on my second hand coil pack, as I'll be keeping it as a spare anyway.

40 miles driven today house hunting and the car was running like a rocket all the way, especially in sport mode. Its a very enjoyable and satisfying car to drive when its running well, this is what has kept me going through the dark times when I never thought it would run well again...

Clearly an ignition fault but just a matter now of pinning down precisely what and where. My hunch is that the difference this time is that I've left out the top two plastic cover bolts so that the edge of the cover is sitting higher and not crushing the spark plug wire against the earth terminal, so that even though the wire may still be damaged its not symptomatic unless its being crushed.

I'm tempted to cut a bit out of the curved piece of plastic on the vent hole to stop it pressing down on the new wire at all. I don't think there's enough slack in the cable to divert it around it...

[Mandrake]

Another hour and a half driving last night house hunting and the car was pulling like a train the whole time

No gradual fading into sluggish, lethargic, "rubber throttle" lack of performance after a period of time as it has so often done before. To be fair though last nights driving was in cold dry weather, but the fact that it ran even better again in the dry air does also point towards ignition related troubles IMHO - I wouldn't expect compressions or fuelling to be affected in any significant way by changes in ambient humidity...but damaged HT lead insulation anywhere between the coils and plugs can make a car very sensitive to high humidity.

Not only was it going like a rocket at higher rpm and/or in sport mode, it was pulling up hills at low rpm in "normal" mode with tons of torque, it was only really last night with it pulling so well that I realised just how lacking in low down torque it has been for so long. 30mph at 1400 rpm up a steepish hill, a small amount of throttle it pulls away quickly and effortlessly with the torque of a diesel

So I'm 99% sure now that the intermittent engine performance/misfire problems that have been dogging me for so long have been ignition/spark related, even if I'm not completely sure how much of the problem is coil pack and how much is plug leads. (Remember both have been changed before, and at one point I thought the new coil pack that is now back in the car was faulty...)

On the weekend my plan is to take the top plastic cover off and leave it off (for a week or two) and apply a couple of layers of 3M self amalgamating tape on the suspect areas on the spark plug leads where I think there might be some damage - in particular where the leads emerge from the top of the plastic cover where the right hand wire gets crushed against the earth lug by the plastic cover and has a bad kink.

The idea is to take the physical strain off the wires by removing the cover, add extra insulation and physically move the wires a bit further away from the nearby earth lug, all in an effort to minimise any possibility of high voltage leakage/arcing from damaged insulation.

If that makes the car run even better and more consistently for at least a few days, maybe a week, then the next step is to put the original ECU back in for a week and see that it doesn't deteriorate with the ECU swap - I don't want to both change the ECU and change/disturb the ignition wires at the same time.

Ultimately if I can prove there is damage to the wires (either during fitting or DOA) I guess I'll have to replace them AGAIN, and try to provide extra physical protection for the wires where they're vulnerable and/or somehow reroute the wire slightly so its not pinched between the cover and the earth terminal. (Or modify the cover)

Has anyone else thought the factory routing of the right hand most plug wire near the top of the plastic cover is a bit dodgy and poorly designed ? And do your V6's have a kink in that plug wire at that location from the plastic cover digging into it ?

[xantos]

Nice to hear some good news from a Xantia owner

It's a shame that you probably won't make it to 100 pages

[CitroJim]

It's a shame that you probably won't make it to 100 pages

You wanna bet?


Simon, good news finally. Excellent stuff

[Stempy]

If it's running well then for petes sake leave it alone!!!!

[Mandrake]

If it's running well then for petes sake leave it alone!!!!

Can't though - I know its not permanently fixed at the moment because I only changed the coil pack and I know the coil pack I took out is almost certainly ok and that the one I've now put back in was was one that was previously misfiring badly before I last took it out last spring.

My conclusion (also based on other evidence) being that rather than being unlucky enough to have 3 faulty coil packs including one that was new, that the swap has simply disturbed the fault.

If I just leave it alone and don't identify the real problem conclusively then as sure as the sun rises and sets it will start playing up again, it's just a matter of time whether days or weeks, and even over the last few days although its running massively better it's still running best in dry air and not as well in damp wet air which suggests there could indeed be an HT lead problem and that its running better since the coil pack swap simply because leaving the top two screws out means the HT wire is further away from the earth lug than it normally would be.

I have some ideas on how to check the HT leads so we'll see where that leads us...

[Stempy]

Many moons ago in the days of CRT televisions we had a spray that you squirted on the anode cap to stop them arcing over in damp houses or those with heavy smokers. Probably on the COSHH banned list now though...