CitroJim wrote:Simon, I forget now but have you replaced the leads?
Yes I have, twice...
The first pair I fitted around September last year - shortly after the new coil pack - after that it still didn't run properly. A month or so later I discovered a small tear like a flap of skin in the black outer sheath of one of the wires due to the teeth in one of the guides nicking it - I taped it up and suddenly it ran perfectly for two weeks.
Happy that I'd found the problem I then bought a second set of leads around November, took extra care to fit them carefully (although no matter how careful you are, getting them into the guides above the inlet manifold at the correct length so the cables reach at both ends is tricky) and it never ran properly like it did with the previous leads with the damage taped up...
Of course at the time you assume it must be something else - new leads, extra care fitting them, surely they can't be faulty, right ? So I moved on to investigate other things, and ruled out the possibility that the leads might in fact be causing trouble again.
But I've now come full circle - definitely an ignition misfire and an electrical fault of some sort, but its not the ignition primary drivers, (proved by the symptoms returning despite the substitute ECU still being fitted) it can't be the coil pack unless I'm really unlucky to have the original faulty, second hand replacement faulty, and new replacement all faulty!
It's not spark plugs - this time it has the correct types in and when I removed the previous set (which were also the correct types) their condition was impeccable with clean white insulators, unlike the dirty fouled ones that came out the time before that. (which were the wrong types - my mistake)
That leaves the spark plug leads as the only other ignition component, so although I've already replaced them I have to face the possibility that either they're faulty from new (very unlucky for me if so) or that despite my extra care they've been damaged again, somehow.
The inlet manifold has been off so many times in the last year that its possible that they've been damaged or further damaged because as you know the wire routing and lack of spare length is such that a lot of strain is put on the leads every time you remove and fit the manifold...yet I haven't been able to see anything wrong with the leads, at least not the parts I can get to.
One thing that's very odd about the first replacements that got the hole in them is that I later cut the lead open and found there are two layers - a black sheath and an inner white insulator which looks a bit like Teflon or polyethylene foam - most of the insulation thickness is the white Teflon like substance, yet in the faulty lead the white insulation did NOT look damaged in any way! Only the outer black sheath had a small tear in it.
Yet I know for a fact that the insulation was flashing through at this point because (a) taping it up fixed the symptoms for 2 weeks, and (b) when it started misbehaving again after two weeks the spark had clearly burnt/melted a hole right through the tape at this exact spot, which is only possible if it was flashing through the inner insulation...
So it seems to me that the insulation is not of particularly high quality if its relying entirely on the outer sheath and the inner insulation flashes through so easily...
If you have and you still have the old ones then make up a set of leads using solid wire.
I'm almost completely certain those leads should not be resistance ones and should be solid.
I sense Deja Vu Jim
We've had this exact conversation before a few dozen pages back...
The Citroen service notes from Sedre/Docbackup definitely agree with you that the spark plug leads are NOT resistance types, this is probably where you got the idea from, however both my original leads that came out (which did have two intermittent breaks) and both sets of replacements that I bought, seemingly genuine Bougicord - are resistance leads of approximately 6k ohm, and all have measured as such.
I even managed to find specs online for the part number which agreed they are resistance leads, so despite the Citroen documentation to the contrary, they seem to be resistance leads.
Why they fit both resistance plugs and resistance leads I don't know - given its a waste spark system that's about 18k of total series resistance from two spark plugs and the leads all in series, which seems like a lot.
I don't have any complete leads left unfortunately, the originals I threw away, and the first replacements which had the tear in the sheath I cut the ends off to make up adaptors for my neon spark testers:
I do still have the cassette from that set but it only has stub leads about a foot long on it now.
I'm not sure how I would go about making a solid wire replacement - as far as I can see the leads that go down into the cassette are moulded in and can't be removed ?
By the way to correct a mistake I made in an earlier post - the plug leads are NOT carbon resistance leads, they're wire wound resistance leads with a very fine spiral wire wound on a small former which is then encased within the "Teflon" layer, then within the outer sheath.