My Citroen XM 3.0 PR-Vestige

[Dean]

The engine manuals all say it is an engine speed sesnsor, the lexia calls it a speed sensor, i call it crank sensor, if i unplug the crank sensor the fault remains the same.
The only speed sensor i know of is for the hydractive and is mounted on the speedo cable.

Im hoping its just a few missfires but i shall know later.

D

[Dean]

Phew, no bang on any of the rear cylinders as the whole rear manifold stays cold, the plugs are wet with fuel so injectors are still working, i only pulled them all out and tested them a couple of days ago so im not doing it again at this point, bit odd to have no spark on one bank, i wonder why that would be.......................

Exhaust fitting time first and then i shall look at this missing problem.

D

[Dean]

Exhaust on and put a temporary pipe on the ICV to stop the vac noise, cleaned the wet plugs in the rear bank and re fitted them, started and it was smooth as silk for a couple of seconds until i rev'd the engine, it then started spluttering, shaking, back-firing in the exhaust and nearly cut out.
Checked the coil and across the primary windings i have 00.6 ohms, between the HT terminal and the primary windings i have 05.3 ohm which seems way too low, i was expecting 10.00 ohm ish but it wont register on that scale currently, will look at the specs but it looks wrong to the untrained idiots eye, maybe wishful thinking.

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[MTXM]

Well done for persevering Dean and it does sound you are close to resolving the running issue. If the ignition coil is the problem I could probably help with a replacement. I have now checked my other spares and there is only a single surplus idle valve pipe, so I wonder if one could be supplied by Paul, but please let me know if you are desperate! The attachment of the engine cover is shown in photos below and I do have a couple of partially worn rubbers if required. With regards, Matthew T.

[Dean]

If its your last pipe Matthew then i will source one elswhere it's fine. TBH the coil being the problem is a long shot as i have not checked the coil specs and not firing on just the rear bank? added HT lead length causing increase resistance killing the spark under load is a bit of a long shot, i think its more likely to be rear cam timing out by 180deg which wouldnt be great news but if thats the problem it needs to be delt with.

D

[MTXM]

Hopefully you do have the timing correct Dean and is there a picture during assembly? Here is a shot of my engine for comparison. Regards, Matthew T.

[Dieselman]

A picture really does say a thousand words.

Did you do that one in your sleep, Matthew?

[MTXM]

It was actually my first and only top end rebuild Will and I remember being paranoid about getting it wrong! I know that Dean also cross referenced several other diagrams so quite likely it is some other issue. With regards, Matthew T.

[Dieselman]

I can't see the cam being 180 degrees out as it's a six cylinder, not a 4 cylinder engine. 180 degrees would have meant blocked piston movement.

A dying coil is possible, but why only the rear bank? A check of the ability for he spark to jump a significant gap is all that's needed. About 25mm is good.

[Dean]

Well i looked at all three i think it was, methods of timing the engine up and settled for the marked chain method since my chains were already marked as laid out in the citroen manual and it seemed the most idiot proof method, it called for timing the front bank and having 19 links between the crank sprocket mark and cam sprocket locating dowl mark on the very outer edge of the sprocket, then turning the crank 360degrees plus a further 240 degrees and timing the other bank up the same way. I thought matthew's in the picture above was timed differently at the time but looking again saw he was using the inner lines on the ballancer sprocket marked at 180 degrees to each other, lined up horizontally with the crank rotated 360degrees clockwise from the method i used. I checked and checked and checked again as i didnt want to go tearing into the timing cover once fitted.

This doesnt change the fact i have a spark on all plugs when laid out on top of the engine, i have all injectors working and injecting fuel but when fitted the rear bank isnt firing and when removed the plugs are wet with fuel.

There is one coil, one rotor arm, one ignition control module and one distributor, the front bank is firing fine therefore these components must be working, the rear bank isnt firing at all, the front manifold gets to 110c in about 2 minutes running, the rear manifold i could lay my face on if i could fit it in there so the rear bank has no cylinders firing, the only thing that can be correct and working on the front bank that isnt on the rear is the valve timing, everthing else is shared.

cleaning the plugs did have it running great for 3 seconds and that is the only glimmer of hope i cling to but if the timing is out on one bank i may be able to sort that by just taking off that banks rocker cover and dropping the sprocket off to reposition the chain, we shall see, ive just ordered my Vauxhall Carlton ignition coil which should be here Friday.

D