My Citroen XM 3.0 PR-Vestige

[Dieselman]

Not sure how that can happen on a car with cable throttle.

[Dean]

No, it feels exactly like a modern car with FBW throttle going into limp, it coasts for a few seconds but is still running and if you go for the throttle again its fine.

It must be a fuel delivery or ignition problem, either the ECU doing it or......................the fuel gauge is packing up

The idle behaved odd too, out of gear it idles really low but super smooth, when i put it in gear it lifts the idle to normal 850rpm, take it out of gear and it drops to about 500rpm and steadily and slightly hunts so i think that is a clue..............i can't rule out injectors as every time ive checked them another one has been dead or clogged, i've nearly binned 6 of 12 due to failure and the one i just replaced was much better than the one it replaced but is not perfect.

I need to drive it a bit again to really get a feel of when and how it does it, see what it does locked in gears so it cannot kick down etc

D

[Dieselman]

It's odd that there isn't a code. If there is no fault, why is it doing it?

Could it be the wiring plug being pulled as the engine rocks bacwards under load?

[Dean]

No it can't be that as the way the harness is routed it can't tug at the plug.
This is why i suspected the ECU in the first place as it doesn't seem to bring the EML light on for anything except for test when ignition is on.

D

[sdelasal]

Dean, - i wonder if the ecu is reading the the correct transmission state i.e. neutral / drive? Do you know the correct, factory spec, engine idle speed in neutral and in drive? Drive should be lower. That said, can't see how that would be linked ot the power loss.

[misha]

I think that sdelasal might have the point.Ecu should be programmed differently for a car with manual and automatic transmission,especialy the idle speed.
Some other values could also be different.
When you plug back the original ecu,is the idle speed normal?

[Dean]

Sorry, this is the original ECU for Auto i have fitted and it see's gear selection fine. The manual ECU does not have that function and is always in the Drive state.

Just to be clear idle is too low in neutral and comes up to correct idle when put into gear.

D

[sdelasal]

Dean, prompted by what I thought you said in one of your earlier comments about how you’ve had to wire the throttle sensor, here’s something to consider. Some systems use the throttle position to determine unique modes. So two examples, (1) if the vehicle is moving and the throttle goes to closed, then fuel shut-off is started, i.e. fuel flow to engine via injectors is cut. (2) If ‘wide open throttle’, (WOT), is detected, then the ECU ignores the exhaust gas sensor and goes to open loop fuelling for maximum power.

So that said, and assuming that’s what the Fenix system does, I wonder what would happen in the car if the throttle was wired the wrong way around i.e. (a) the ECU thinks it’s at full throttle when the throttle is actually closed and (b) the ECU thinks the throttle is closed when you are driving the car at full throttle.! I wonder if you are getting fuel cut when you are at full throttle! At idle, the ECU should be controlling engine RPM to either the N value or the D value. It can’t do that unless it’s being told correctly that the throttle is closed, not at WOT.

Two ideas: Simply disconnect the throttle sensor and see if you get correct full power operation. Or change the wiring so the ecu reads the correct throttle state. Steve

[Dean]

I was thinking about this today Steve and I think you are totally correct, the trouble is looking at the Lexia screen the TPS is wired the right way round currently, low voltage at closed throttle, higher voltage as throttle opens, as the manual says.
At Idle the Lexia shows engine state as 'idle' (.8v), when opening the throttle it shows 'Mid' and at WOT it has a signal voltage of 3.8v.

If I wire the TPS as the wiring diagram says then the Lexia always shows throttle position as 'mid' and the voltage runs the wrong way (3.?v at idle down to 1.?v at WOT)

You are 100% right through.................... I shall look at this yet again as I can see no other explanation for the fault I currently have.

D

[Dean]

You were spot on Steve, interestingly, wired up like this it will show 'Idle' 'Mid' and 'Full' throttle, all be it backwards (must of been having another dotty moment) but wired correctly it will not show 'Full' throttle.

Im going to drill out the sensor and try and clock it to get that right.

D