My Citroen XM 3.0 PR-Vestige

[Eddie nuff]

As a mere 4-pot man, not wishing to stick my nose into the antics of you big boys playing with your V6's, my memories of one bank not working are from a while back.

Have you checked the compression on both banks to compare. If the timing is perfectly out of phase, I'd think that your intake would smell of fuel because the injectors would be firing against closed intake valves.

[Dean]

The injectors fire on closed valves all the time as they are not a sequential setup. I suspect I have the rear or front bank 360 degrees out of phase at the crank from the other bank, this would cause the ignition timing to accur at tdc on the exhaust stroke not tdc on the compression strok resulting in a lack of go.
I may have misinturpreted the manual when it said fit front cam chain and turn crank 1 full rotation plus 240 degrees, who knows.

I will replace the coil and stick my new plugs in and then if there is no difference, which I doubt there will be I will pull the timing cover and re-time the engine, should only take a few hours as access is good to that end of the engine when fitted.

D

[sdelasal]

Dean .... how is the ignition system set up on this engine? distributor? coil on plug? If distributor, what drives it? is it possible you have plug leads incorrect? A compression test is simple & perhaps useful to eliminate the unexpected.

[Dean]

Single coil with distributor driven from the front camshaft.
Compression is 10bar on every cylinder.
HT leads are correctly routed and triple checked.

D

[White Exec]

If spark there, fuel there, timing (probably) ok, common single coil and distributor and plug leads correctly connected, there has to be something that is just upsetting the rear bank.

How about AIR to the rear cylinders?
Also check once again that plugs are connected in absolutely the right order.
How fat is the spark at the rear plugs? What distance will it jump? Is it actually being delivered while the engine is running (not just a static test)*?
*Remove one plug lead from its plug, and see what distance the delivered spark will jump to the plug terminal, with the engine running.

A very odd fault, Dean.

[Dieselman]

It sounds remarcable, but is there any way the earth could be interrupted to the rear head?

What would be the effect if the rear knock sensor reported knock? Would it retard te ignition far enough for the engine to fail to fire in reasonable time?

What if the distributor cap has a crack near one of the rear HT connections, would it shut down all three cylinders?

[Dean]

Nope, nope and nope, the rotor and distributor is brand new, i think this is where i stupidly messed things up
IMG_3096 by Deanxm, on Flickr
I took the symbol to mean after fitting the front timing chain to turn the cank 1 full turn + 240degrees before fitting rear chain, i think what it meant was turn clockwise + 240 degrees and thats it.
Compression would be fine, it would sound fine and work as you would expect but the crank would be 360degrees advanced against the front cam position which drives the distributor, this would result in the spark being fired on every rear cylinder at the top of the exhaust stroke, not to top of the compression stroke.

Stupid boy Pike!!!!

D

[Dieselman]

Makes sense.

Matthews picture really was useful. Align the crank marker through the rear bank cam sprocket, align the cam sprocket to the crank and use the 4'oclock marker to align across to the front cam sprocket, both facing into the Vee. If what you say is correct, your rear cam marker will be facing downwards, towards the crank and the cam marker will be at 10'oclock, facing away from the Vee.

Can you release the tensioner and cheat the chain round the cam sprocket?

[xmexclusive]

Hi Dean

Page of text and page of photos about chain refitting.

V611215001.jpg

V611215002.jpg

John

[Dean]

unfortunately not Will as the tensioners are fully compressed but im wondering if i can just take one rocker cover off (rear), remove the cam pulley keeping the cam chain tight to stop the tensioner ratcheting out and then turn it, put it back in the chain and bolt it back on, either that or remove the timing cover from under the two rocker covers and do it like that.

I think for a little more work its worth taking the timing cover off but leaving the rocker covers in place to get full access to all the timing marks, dont want to fudge it up twice now do i!

Thankfully there is loads of space at the timing end of the engine, much more than the 4 cyl lumps have for obvious reasons.

Still cant believe i made that dimwit mistake, oh well, a days work will see it right.

Thanks John

D