The V6 misfire mystery continues

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Stempy
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Joined: 26 Feb 2004, 23:21
Location: Cloud Cuckooland
My Cars: C5 V6 Mk1 assainated by wife
Renault Kangoo 1.6 auto, tarted up and remapped
Still missing the Xantia V6
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The V6 misfire mystery continues

Post by Stempy »

So.. a big thanks to Richard Gallagher for plugging my Xantia into his diagnostic tool.[8D] No fault codes showed unfortunately but it did show that all the various sensors and actuators were working correctly, the only possible fault that showed was that the coil for cylinders 2 & 6 was taking twice as long to charge as the other two. I'm assuming that pistons 2 & 6 are both at TDC together and one is a wasted spark. Anyone had a duff coil pack on a V6? Anyone know how to check a coil pack?
David Goddard
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Post by David Goddard »

I recall you changed the spark plugs recently. Did you have your misfire before then?
If the engine was OK before, is it possible that the plugs for either cylinder 2 or 6 are faulty or (more likely) the rubber lead connectors may not be perfectly clean. If one or the other has a problem, being a wasted spark system, ignition of 2 cyliders will be affected.
I had a similar problem due to coolant spilling down one of the plug recesses.
alan s
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Post by alan s »

Stempy,
When is it misfiring? At idle, cruising, under load?
If all the sensors are testing OK, it could ba as David has suggested to do with plug leads but I'll add even further. It's possible that it may also be shorts on the leads associated to the coils alao.
I realise you have a different set up to my BX as I have a distributor & you apparently have coul packs, but on teh BX, a common cause of misfiring at cruise, light load, is that the LT plug into the coil has both + & - terminals in there. When there is a build up of grime, this grime tends to become conductive, particularly after it's been disturbed for any reason and can only be removed by careful & detailed cleaning.
I usually wash in WD 40 (coil, plug, wires; the lot) and wash the WD off with petrol & blow dry.
Sometimes this has to be repeated several times before it is effective but we've found it so often, it's the first thing we do now with a car having a miss.
Costs nowt & worth a try.
Alan S
Stempy
Posts: 1626
Joined: 26 Feb 2004, 23:21
Location: Cloud Cuckooland
My Cars: C5 V6 Mk1 assainated by wife
Renault Kangoo 1.6 auto, tarted up and remapped
Still missing the Xantia V6
Not missing the AX
Contact:

Post by Stempy »

The engine was misfiring before I replaced the plugs which was one of the reasons I changed them. The misfire occurs mainly when cold but is still apparent sometimes when warm, and it usually happens under light load such as when pulling away on a gradient at revs between idle and around 2200. I'll certainly give it a good old scrub up and see what happens.
alan s
RIP 2010
Posts: 2542
Joined: 26 Jan 2001, 15:53
Location: Australia
My Cars:
x 6

Post by alan s »

That is exactly when this problem with the tracking occurs; be thorough with the cleaning and particular with the washing off & blowing dry. It can also be made worse if the caps on the plugs are old & as a result the metal inner part is not making a tight connection with the plug. This causes the spark to intensify & will, amongst other things, cause shorting through insulation anywhere there's a weakness.
If it can be made do it when the car is stationary, parked in a dark spot with lights off at night can sometimes make locating the source of the shorts very easy.
Alan S
Stempy
Posts: 1626
Joined: 26 Feb 2004, 23:21
Location: Cloud Cuckooland
My Cars: C5 V6 Mk1 assainated by wife
Renault Kangoo 1.6 auto, tarted up and remapped
Still missing the Xantia V6
Not missing the AX
Contact:

Post by Stempy »

Well I've given the coil pack and all of the leads that are visible a thorough clean in isopropyl alcohol but the misfire remains. I feel that sinking feeling of having to remove the inlet manifold again to get to the rear bank of plug caps. In the meantime I'll try to find a dark spot to see if there's anything visible. Anyone know which cylinders are actually 2 & 6?
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