Citroen XM V6 Bad Running

Joe T · Post by **Joe T** » 31 Jan 2006, 15:03

It does look like a pukka repair done with a heat gun etc.

One question if the injectors were faulty would it be like plug failure?, I saw nothing strange when I hooked up a pressure gauge to the fuel rail.

Also does a faulty lamda show up with bad CO.

I just cant beleive I can't fix this!!!!!! the fault is so reproducable, I just start it from cold, let it tickover for about ten minutes to warm up, then drive it and the faults there straight away. I can actually here it when it stationary and you rev it.

Shame really the old bus still drives better than most other things I have tried, even the co pilot I let have a go remarked on how smooth the ride is and quiet etc.

I wish whatever it is would just die and break down, I carry around a box of spares in hope!!!

jeremy · Post by **jeremy** » 31 Jan 2006, 17:55

Injectors spray fuel into the manifold and the spray pattern is important. The idea is to produce a very fine mist which hangs around in the manifold until its drawn into the engine. If the injectors get dirty they may not atomise properly - and produce bigger droplets which don't burn as well. bit like diesels really but all at very much lower pressures (36 psi or so - diesels 1500 - 2000 psi - several times that for modern electronics)

Some injectors simply spray (Bosch K jetronic - which was a simple but effective system which sprayed all the time!). Electronic systems are electrically controlled by the ECU and in fact fire every engine revolution. The injector contains an electrically operated valve controlled by the ECU. The ECU controls the length of time the valve is open and so you will see that both functions are essential.

davehughes · Post by **davehughes** » 31 Jan 2006, 17:58

I don't know anything about petrol citroen engines but used to be a bit of a BMW expert. My suggestion is do they have an airflow meter. I repaired a car with a problem like yours by replacing the air flow meter. The airflow meter I beleive has some link to temperature as well.

Joe T · Post by **Joe T** » 01 Feb 2006, 12:21

Thanks Guys, understood on the injection process, how do I diagnose a faulty one?

No Air flow meter on the XM V6 but know the fault you mention I had a GTI Visa once, cracking little car and the flow meter died on that.

I have been told that Autodata do a CD with all the meter readings on for the sensors etc, is this worth a go. Baring in mind the computer records no faults??

FrenchLeave · Post by **FrenchLeave** » 05 Feb 2006, 23:23

Joe,

Only just seen this post so a bit late in sticking my oar in. Are any of the spark plugs relatively easy to get to or are they all bu**ers like the late model Series 2's? I wondered if it would be worth while clearing the ignition system of blame by waiting until the fault is present, then pulling a plug lead and connecting it to a spare external plug and checking to see if the thing is sparking during the flat spot stage. That would at least isolate the problem to either the fuel system or the ignition system.

Derek

Joe T · Post by **Joe T** » 06 Feb 2006, 15:22

I did leave the top engine cover off for quite some time, but have tried a couple of sets of plugs.
Determining whether its ign or fuel would be very useful but I have changed all the ign system I believe, from plug to ECU. But happy to investigate any parts I have missed.

For clarity removing a plug then driving the car reduces the overall performance, not as drastic as a 4 cylinder car, but you can still feel the fault thought the general lack of power, this is the same as removing sensor plugs.

I have sort of come to the conclusion I may have replicated the fault with a secondhand part, bit depressing but I doubt I could afford to buy the parts I now transport about in new form.