Citroen XM Forum

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

That is an extremely kind offer Rob and I shall certainly let you know if I do not manage to secure one elsewhere. The Lexia does indeed require Window XP to set up and run. With regards, Matthew T.

Evening All!!
Here is some data from my Lexia session with Steve earlier today. I shall add more comments shortly!
Regards,
Matthew T.

And for comparison some data from the gold car.

Not significantly different and the oxygen sensor appears to be working properly, flitting between a lean mixture and a rich mixture.

As you note the O2 sensor is now behaving correctly on the grey car Will and interestingly also the throttle sensor! The only conspicuous difference between the two cars is the mixture % readings, which on the grey car are always in the negative that cannot be right surely! A number of other observations were made during the session that may or may not be significant but the last one certainly is. After cranking with a dying battery fumes were seen emitting from the intake manifold that was subsequently found to be absolutely swamped with fuel! I now attach photos of the manifold after removal of some fuel and the fuel itself presumably soiled by accumulated dirt inside the chambers. Any ideas as the cause of the latter - surely jammed injectors would fill the cylinders not the intake manifold? With regards, Matthew T.

The most significant difference that I see is that your grey car is showing lower efficiency of 340 mb @ 2688 RPM against 308 mb at 2720 RPM.

This could be caused by low compression, incorrect timing, or a restricted exhaust (or other things).

Lower thermodynamic efficiency will also cause the negative mixture correction that you are seeing, as the ECU fuelling map assumes the normal relationship between manifold pressure and air flow.

The fuel in the intake will be the remains of whats been thrown in, manifold pressure is the only difference i can see although the i still think they grey car is reporting a richer mixture via the O2, difficult to tell with stills though.

Just out of interest i would do a compression test, should be about 10bar

D

The fuel in the intake will be the remains of whats been thrown in

Really Dean!! Surely the fuel is 'thrown in' the cylinders, not the the manifold, whose inside was just awash with petrol. The photo is taken after siphoning out what I could and I reckon at least 3/4 pint was standing. I wondered whether the fuel arrived via the regulator breather hose? Regards, Matthew T.

Mixture readings

Grey car/ Gold car

600/800 rpm -18% and +7%
1,500/1,600 rpm -15% and +9%
2,600/2,700 rpm -22% and +19%

I think these differences are really significant!

The readings confirm the engine is being starved, which is fundamentally the problem, as graphically illustrated by hand pouring in the petrol. I just need to establish what is holding back the fuel.

Regards,

Matthew T.

MTXM wrote:

The fuel in the intake will be the remains of whats been thrown in

Really Dean!! Surely the fuel is 'thrown in' the cylinders, not the the manifold, whose inside was just awash with petrol. The photo is taken after siphoning out what I could and I reckon at least 3/4 pint was standing. I wondered whether the fuel arrived via the regulator breather hose? Regards, Matthew T.

If your fuel pressure reg diaphram had split it would give low rail pressure i would think but be pouring fuel into the manifold, easy to check, just pull the vac line off the regulator and start the car to see if fuel comes out of the regulators vac connector.

The intake is designed as a chamber with the intake runners in the roof so if you were just dribbling fuel into the throttle body all of it would be atomised and drawn through with the air into the cylinders, dumping the fuel in will cause some to be atomised but most will just drop into the bottom of the intake where due to low air speed it will just sit.

At this point (looking at the live data between a good and poorly car) i would perform a quick compression test, its not likely to reveal a problem but its time to go back and check starting with the basics to rule them out. i would then make sure you have no ground leaks on the HT side of the ignition before going further. Pull the vac line on the fuel pressure reg to confirm that it is just the fuel you tipped in and not a dead reg.

Im wondering about the TPS voltage suddenly sorting itself out, thats odd, so if the above check out fine i would be looking for a bunch of pinched wires.

I would also be wondering why with such a critical fault there was no EML light on, are you sure there is not a physical fueling or exhaust restriction?

D