Citroen XM Forum

The Lexia test will be interesting.
Your earlier test (video - chucking in a cup of fuel) does rather suggest fuel starvation - i.e. injection, or lack of it.

Thank you Chris and repeated the cup of fuel test earlier today just to check nothing had changed, with the same satisfying result! The engine is clearly being told that it does not need fuel when it does, which if the last Lexia test is to be believed is a combination of distorted/incorrect O2, TP and MAP sensor readings. The question is what might cause this situation to occur, given the ecu, sensors and wiring all appear to be in order? On a more positive note I attach pictures taken earlier today and the gold car at least is a joy to drive. With regards, Matthew T.

After some further checks I have found a disparity with the wiring compared to another car in that one additional ecu terminal appears to go to earth! The ecu terminal is no.32, which does include the O2 sensor circuit and front and rear knock sensors, so that might be what is upsetting the Lexia reading, apart from the running of the car! I am not sure what is causing the further earthing at present other than a possible short circuit somewhere and any suggestions would be most welcome! Regards, Matthew T.

those three sensors should be earthed together to the inlet manifold via the ECU, i remember seeing that on my early loom, think the blue canister purge valve uses that ground too.

D

That is helpful Dean, but I wonder why terminal 32 does not apparently go to earth on the other car? Does it look like there should be an earth at 32 on the diagram? Regards, Matthew T.

Matthew - 32 looks like a signal common return to me - i assume you are testing with the ecu disconnected and so you are seeing a (mis)connection /short to earth in the wiring loom. To try & determine where, you could disconnect the o2 sensor, then knock 1 (151) then knoock 2 (152) - (added afterthought: I see a couple of temperature sensors too that are connected 907 & 909).. one at at time and see if the continuity to earth disapears. That should help you figure out whether the earth is in a faulty sensor or in the wiring.

That wiring diagram is hard to follow - 151 & 152 are shown with a connection to terminal 2 on the ecu (earth) - via those thick black verticle rectangles - do you have a key explaining what that symbol means? Are the knock sensors earthed via the engine block ? Do they have a 2 or 3 pin connector?

Is your lexia working?

Hi Matthew

Might be worth looking again at XM 1-52 that I posted in this thread on 17 Feb.
Fault symptoms are very similar to yours.
Diagnosis is wrongly wired Oxygen sensors destroyed them.
ECU pins 32 & 35 are mentioned.

John

Apologies for the late response and in the meantime I have found the my other early V6 also has earthing on ecu pin 36, so it might be a change to the wiring and not the issue as I had thought! I have definitely not wrongly connected the 02 sensor plugs John as I did this on my rhd 24v earlier and learnt the lesson. The laptop arrived today Steve but unfortunately dos not have Windows XP as advertised that is needed for the Lexia!! With regards, Matthew T.

Matthew, I have a couple of surplus XP laptops. Let me know if you need one posted out.

Rob

XP...XP...! DOS is what you need.