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

[myglaren]

Gosh Three days away form the forum and this thread has grown like topsy again...

You sound suprised Jim.

Maybe because I'm suffering from a bit of rough running today and feeling distinctly down on power

You may need a fuel additive Jim

[CitroJim]

You may need a fuel additive Jim

Chilli might do the trick!!

[Northern_Mike]

You may need a fuel additive Jim

Chilli might do the trick!!

<jokes about chili clearing Jim's blocked exhaust are banned>

[CitroJim]

You may need a fuel additive Jim

Chilli might do the trick!!

<jokes about chili clearing Jim's blocked exhaust are banned>

[addo]

It's the particle filter I'd be worried about...

[Mandrake]

Ok funny guys, make way for real news.

PROGRESS!

Today I had to go on a 40-50 mile trip and something had been gnawing away in the back of my mind for weeks now, almost completely on a hunch with no real troubleshooting or theories behind it before leaving on the trip I took out the new coil pack that I fitted some time late last year and put the original 15 year old one back in. I had kept the original as at the time fitting the new coil pack made no change either for better or worse, so I thought it would be wasteful to throw the old one out if it was still good. (I later discovered that it was the rear bank plug leads that were faulty at the time, NOT the original coil pack)

Well blow me down if this thing isn't running almost normally now. There's an enormous difference in performance from before, not quite perfect but on a scale of 1-100 I would say performance has gone from 40-50% of normal to about 85-90% of the best I've ever seen out of it. As soon as I started it it settled into a steady miss free idle with no visible rocking of the engine - in the last month or so there has been a miss every second or two at idle where you could clearly see the engine rock with each miss.

Pulling at lower RPM is hugely better and when you kick it down it really pushes you back in your seat now.

So what is going on guys ? Have I been the unfortunate victim of a new replacement coil pack failing on me in just over 6 months ? Or have I simply disturbed some faulty wiring ? All I did was pop the bonnet, remove the top plastic engine cover, unbolt the coil pack, put the new one in (same boots off the old coil pack used) put the cover back on and start the engine and the idle was perfect from the get go. I didn't disconnect the battery or mess with anything else, and I still have my dodgy negative terminal in place.

Performance did sag slightly after 50 miles of driving but only a little bit. I would put some of that down to the changes in torque converter lockup strategy with temperature - when the gearbox oil is fully warmed up the ECU more aggressively uses lock up (disabling half throttle TC unlock) and also doesn't kick down as easily which can make it feel like there isn't quite as much oomph, but if you manually change down the power is still there.

Another possible factor is the inlet air temperature gets quite high after the engine bay is really thoroughly heat soaked - even on a 17 degree day like today the inlet air through the butterfly is around 45 degrees by the end of a long trip which will reduce the volumetric efficiency a bit. (It could have done with an intercooler! )

I'm not even convinced that the original coil pack is 100% but its running one hell of a lot better than the new one, unless it really is just a case of disturbed faulty wiring. I wiggled the coil pack primary plug and wires on the left hand end of the coil pack vigorously after the old coil pack was fitted and I couldn't get it to miss, so if its faulty wiring its not at that plug.

When I had the manifold out to do the fuel pressure regulator the other day the wiring loom did get tugged on and moved around quite a bit, so any dodgy wiring might have been provoked at the time...but in all the testing and work that I've done over the last 6 months I've never found any actual evidence of poor/intermittent wiring.

I even checked the strength of the spark from each coil only a month ago, and all were able to easily jump 20mm, so I found no evidence of a weak spark, but clearly there must have been a weak spark causing a misfire under load. Again. (already fixed that problem once with new plug wires last year)

The lean oxygen sensor reading under wide throttle I reported recently makes sense now too - unburnt oxygen from the misfiring cylinder(s) passing through to the oxygen sensor. That and the intermittent miss at idle were the only clues that something was wrong with the ignition. Again.

I guess we now wait and see how long this lasts and whether it goes bad or not, (I'm not doing any cartwheels yet) but we have a very large very obvious jump in performance after touching only a very limited number of things. It really can only be the new coil pack failing, or a loose/intermittent connection somewhere in the wiring loom.

If it is the coil pack you can see why I've been banging my head against a wall trying to diagnose this car - why would I ever expect that the brand new coil pack would fail on me in a few months ??

[Old-Guy]

Delighted to see that your problem has gone away.

Not experienced it personally, but I do know of a similar case where a new coil pack (pattern part) failed after a few months. Needless to say, that supplier has lost a customer!

[Mandrake]

It's not a pattern part though Old-Guy, its an OEM Sagem unit, and looks identical to the original including the logos. Unless its a very good counterfeit its the real McCoy! I think I'm just unlucky...

[CitroJim]

Simon, that's excellent and bears out my findings a few weekends ago when a poorly running V6 was transformed by the replacement of its pattern part coil with a genuine, albeit second-hand OEM one...

The next thing for you to check is your economy... I still reckon that's a good guide to how well a V6 is running. Mine in the XM has been transformed economy-wise since replacing the dead oxygen sensor.

[Mandrake]

Simon, that's excellent and bears out my findings a few weekends ago when a poorly running V6 was transformed by the replacement of its pattern part coil with a genuine, albeit second-hand OEM one...

Where was the pattern part from do you know, and was it Sagem or something else ? I can't quite recall where mine was from but it was claimed to be OEM not pattern, and was from a clearance sale, think I paid about £80 for it.

What were the symptoms ? Lack of power overall but particularly low down ?

The next thing for you to check is your economy... I still reckon that's a good guide to how well a V6 is running. Mine in the XM has been transformed economy-wise since replacing the dead oxygen sensor.

The funny thing is my economy already went up from 19MPG to nearly 23MPG around town with the 99 octane fuel, with the faulty coil pack! In theory it should be better still now, if I can keep my foot off the loud pedal now its running so much better. (A V6 is not for driving Miss Daisy )

[CitroJim]

It was generally rough running Simon. Stumbling on pickup, misfires and popping in the exhaust on occasions...

The coil pack - still have it - is an Intermotor - a well enough known maker of pattern ignition parts...

In theory it should be better still now, if I can keep my foot off the loud pedal now its running so much better. (A V6 is not for driving Miss Daisy )

If only you can try moderating your driving you will find a well-sorted V6 can be very economical. I see around 35mpg out of mine on my regular forays into Somerset and I reckon the XM has the edge. Maybe because it's more aerodynamic or how I drive... The XM imposes a different sort of driving style; a laid-back gentle one. the most pointless part of my XM is the sport switch It's never used.

Those that know me do know my driving style is quite moderate.

[Mandrake]

It was generally rough running Simon. Stumbling on pickup, misfires and popping in the exhaust on occasions...

Apart from popping in the exhaust, the same symptoms I was seeing, although I suspect mine was a lot worse.

If only you can try moderating your driving you will find a well-sorted V6 can be very economical. I see around 35mpg out of mine on my regular forays into Somerset and I reckon the XM has the edge. Maybe because it's more aerodynamic or how I drive... The XM imposes a different sort of driving style; a laid-back gentle one. the most pointless part of my XM is the sport switch It's never used.

Those that know me do know my driving style is quite moderate.

Don't worry Jim, I'm no Xac. My driving is really quite moderate and smooth most of the time but I like to open it up sometimes, where its safe of course. I like to have the power on tap and have the responsive throttle even if I'm not using it all the time.

[Ben82]

Haven't managed to get 35mpg out of my C5 yet, but the killer is probably the many junctions to get out on the open road from where we are.... Yesterday I managed to get the consumption down to 9.6l/100km (29.4mpg), over the past ~450km (about 250km of that was usual trips, and the other 200 was a round trip to the zoo). Currently she sits at 9.8l/100km (28.8mpg)... I have found two techniques that have helped a fair bit on this tank. One being that I use the sequential mode when accelerating and don't let the engine get above 2K before changing up a gear, so she only goes above 2K in 4th. The other is for coasting around our residential area (speed limits of 30-50km/h) I stick it in 4th and let her coast around, and she keeps the speed up pretty well.. The engine completely idles when doing this at 30km/h (around 1K in 3rd and about 600 in 4th). (I guess the latter you can't do in the Xantia/XMs due to only being able to select 1,2 and 3 or Drive).

It's strange that the ES9J4S is supposed to be more economical than the ES9J4 (mainly due to the VVT if I recall?), so whilst I'm thrashing Simon's mpg, I'm still a fair way off Jim's economy figures.

[Mandrake]

Oi!

Jim's 35 MPG figure is for long trips on the motorway, my 19-23 MPG figure is for urban 30mph stop start driving.

On a long motorway/country roads trip I've seen 32.8 MPG from this car (before it started behaving badly last year) averaged over 800 miles with 4 people and a boot full of luggage, and I wasn't shy about using the overtaking lane either.

On the motorway the 3 litre auto does the same MPG I used to get from my 2 litre auto... its in the slow stop start urban traffic that the V6 suffers.

[CitroJim]

I like to have the power on tap and have the responsive throttle even if I'm not using it all the time.

That's precisely what I like about the V6 and find dangerously lacking in smaller offerings... Not that I use it often but a good reserve of power can be a great safety aid..

I also like the big brakes too...

Some small engined cars I feel positively unsafe in. One I don't is the Activa as despite only having a small engine it's not short on urge in all the right paces