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

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

Post by Mandrake »

If you get a chance to check the location of the relay in a Series 2 that would be very helpful Jim :) I'm hoping to fit the relay on Saturday so if I can avoid removing the wheel arch liner unnecessarily I'll be a happy lad :)

I have a suspicion that my car being a very early S2 may be a S1/S2 crossover "mongrel" that has the relay in the Series 1 location. The wiring diagrams certain say so, and none of the relay sockets in the foot well seemed to be the correct one when I was doing voltage checks. Also pin 6/7 on the ECU are wired in the Series 1 fashion not Series 2.

For full details see:

http://www.frenchcarforum.co.uk/forum/v ... =3&t=45265" onclick="window.open(this.href);return false;

The good news is that thread is only 2 pages long :lol: and most of the posts are just speculation by various parties as to where the relay resides. :twisted:
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Mandrake
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Re: Xantia V6 broken exhaust (update: and rough low rpm runn

Post by Mandrake »

Started the old girl up today - nice warm dry weather, happened to have the door open while starting, and heard distinct intermittent "popping" in the exhaust for the first 20 seconds or so that the engine was idling which then went away but still popped a little bit when revving the engine.

Strangely the car was running okish while actually driving, although it does tend to run better on warm dry days anyway.

Is the exhaust popping consistent with an ignition misfire ? I can't imagine it would be a lean misfire on a cold start because the oxygen sensor will not be active during the first minute or so and the ECU will still be applying cold start mixture enrichment.

I replaced the ignition suppression capacitor yesterday too, it disintegrated in my hands when removing it (the earth tag broke clean off with the slightest bump) but that's a story for another post...
addo
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Post by addo »

Like 10mm gravel in a jam tin sort of noise?
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Mandrake
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Re: Xantia V6 broken exhaust (update: and rough low rpm runn

Post by Mandrake »

No, like overrun cackle, except at idle. Maybe one or two pops a second.
larppaxyz
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Re: Xantia V6 broken exhaust (update: and rough low rpm runn

Post by larppaxyz »

Mandrake wrote:Another possibility that I'm investigating in relation to false knock sensor retard is replacement of the ignition suppression capacitor mounted above the coil pack:
I think i didn't tell last time that i also umounted that capacitor, it is cracked just like yours. I wanted to see if it's connected to ground properly as i'm still thinking there could be some issues with negative side. Anyway, i pulled wire directly from this capacitor to chassis (close to right, headlight) where i knew was good connection to ground. Capacitor is of course still connected to engine.

Sadly, it's impossible to see big ground cable coming from battery to engine. I can feel it but i can't see if it's all good. So that's why i pulled one extra wire to location where i know that there is good connection.

It's been around three or four weeks since i did that and it's been much better. Not perfect still, but there is no 3500rpm lag appearing yet.

Right now my car is waiting for new belt(s), tensioners, water pump and most importantly new engine mount rubbers. Cost ~1000 euros inc. labour.
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Mandrake
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Re: Xantia V6 broken exhaust (update: and rough low rpm runn

Post by Mandrake »

larppaxyz wrote: I think i didn't tell last time that i also umounted that capacitor, it is cracked just like yours. I wanted to see if it's connected to ground properly as i'm still thinking there could be some issues with negative side. Anyway, i pulled wire directly from this capacitor to chassis (close to right, headlight) where i knew was good connection to ground. Capacitor is of course still connected to engine.

Sadly, it's impossible to see big ground cable coming from battery to engine. I can feel it but i can't see if it's all good. So that's why i pulled one extra wire to location where i know that there is good connection.

It's been around three or four weeks since i did that and it's been much better. Not perfect still, but there is no 3500rpm lag appearing yet.
I intermittently see "lag" or lack of power below 3500rpm when cold - for example after a cold start if I drive away soon after starting, when accelerating in 1st gear up hill there is a big lack of power below 3500 rpm, then as soon as the engine reaches 3500rpm the power suddenly returns and the car abruptly accelerates.

This problem does not always occur (it happened yesterday morning but not this morning) and usually goes away after a few minutes of driving. I'm still not sure what causes it. :? I'm pretty sure its ignition related, but cant narrow it down further than that so far, nor confirm whether it is the same fault causing general intermittent power loss or is a separate problem.

I've been meaning to post pictures of my capacitor replacement - when I took the top cover off the engine a few days to fit my new capacitor I found this:

Image

As you can see the back of the housing around the prongs on the earth connector had chipped away completely by itself in the last few weeks since the plastic cover was off. While removing the capacitor I could tell the earth tag was barely hanging on, a little bit of wiggling and it fell right off:

Image

The top two prongs are mechanical support for the earth tag and rely on the top cover still being present, once the cover cracked and chipped away there was nothing supporting the prong except for a dry soldered joint on the third prong which was barely hanging on...

Here is the replacement capacitor - the same type linked to earlier, which can be had for about £4:

Image

It's a bit smaller, but a perfect fit, the only thing I had to do was slightly ream out the diameter of the hole to fit the bolt.

I'd like to say that I could notice an improvement with the new capacitor but the truth is that I haven't noticed anything conclusive at the moment as the running symptoms are still very intermittent. It had to be replaced though because it was literally falling apart...

Unrelated to the capacitor I had a closer look at a "crack" in the top of the coil pack primary plug, on closer inspection it looks more like someone has slitted the top of the plug open, perhaps to try to back probe the connector ?

Image

Does anyone think this looks a bit dodgy ?

I wish I had a current clamp for my scope so I could measure the coil primary current waveforms...that's one thing that has never been checked, I would be kicking myself if this intermittent loss of power turned out to be a weak spark due to a dry joint inside the ECU in the ignition driver section! #-o

Is there any history of dry joints in these ECU's or is it very unlikely ?
addo
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Post by addo »

It's quite normal for the overmould to split from heat and age. Wouldn't sweat it.
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Mandrake
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Re: Xantia V6 broken exhaust (update: and rough low rpm runn

Post by Mandrake »

Thanks, I won't worry about that slit then.

Well the coil pack (and fuel pump) from KP's breaker have been paid for and dispatched and should be here by Monday.

Will the coil pack fix the intermittent misfire ? Let's see... [-o<

I'm guessing that if its been misfiring badly enough for long enough one or more plugs will be badly fouled like last time, which may mean new plugs and a new manifold gasket again... :? Not expensive, just annoying to have to do that again, but we'll see if its needed or not.
Stempy
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Re: Xantia V6 broken exhaust (update: and rough low rpm runn

Post by Stempy »

If it's running right an Italian tune up will soon clear the plugs
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Mandrake
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Re: Xantia V6 broken exhaust (update: and rough low rpm runn

Post by Mandrake »

Stempy wrote:If it's running right an Italian tune up will soon clear the plugs
Maybe, if they're not fouled so badly that they don't fire at all, this is how they were in cylinders 4 and 5 last time, fouled so badly they wouldn't clear by themselves: (and that was after only 3 months and less than 1000 miles from new)

Image
Image

Mind you those plugs were a heat range colder than the ones in there now, so maybe they will clear this time with an Italian tune up. :twisted: I get the impression though that a large part of the misfire I'm now seeing (particularly at idle) is once again fouled plugs, (symptoms are very similar to last time thinking about it) but of course something must be causing them to foul in the first place.
Stempy
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Re: Xantia V6 broken exhaust (update: and rough low rpm runn

Post by Stempy »

You do realise that you don't need to add two-stroke oil to the fuel :-D
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Mandrake
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Re: Xantia V6 broken exhaust (update: and rough low rpm runn

Post by Mandrake »

Ah, that's what I'm doing wrong then. :-D
addo
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Post by addo »

They don't look "sooty" - especially the second image.
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Mandrake
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Re:

Post by Mandrake »

addo wrote:They don't look "sooty" - especially the second image.
Not sure what you mean ? They look pretty sooty to me. On the second one you can actually see "tracking" where the spark has been burning a path along the carbon on the insulator rather than firing across the gap.

Here's all six for context, they were removed a few months ago.

Cylinders 1,2,3:

Image

Cylinders 4,5,6:

Image

Perhaps the difference between the plugs provides some clues. The front bank looked good, the rear bank not so much.

By the point these spark plugs had been fitted the faulty spark plug leads to the rear cassette had already been replaced, so its not a case of bad spark plug leads causing the rear plugs to foul...
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Post by addo »

The only really sooty (as in, oily or cold burning) one to me, is the bottom left. The others just suggest richness or ill-timed combustion.