My Citroen XM 3.0 PR-Vestige

[White Exec]

Progress. Well done.

[Dean]

Drilled TPS mounting holes out (need to do both as it needs to be clocked, you cannot cant it) to 5.5mm before i could get the sensor to show idle, mid and full throttle state. I also needed to adjust the throttle stop pin slightly but we are now there.

I cannot start or drive the car though as the woman is out with other women doing some sort of odd PTA wine drinking event and the animal is in bed.

Optimism is high as is potential for further failure

D

[sdelasal]

Good news, fingers crossed then! Seems odd though to have to resort to modifying the sensor/throttle mounting/assembly. Perhaps the sensor/bracket/throttle body parts are non-standard? Steve

[White Exec]

Optimism is high as is potential for further failure

To quote Jon Cleese from the film Clockwise, "It's not the despair I can't stand; it's the hope . . ."

[Dean]

All parts are OE Steve, it just wont quite make full throttle and even now i've modified it you can anly get the ECU to see "Full throttle" if you really stamp the throttle plate into the stops.
I wonder if there are other 12v V6's out there who's ECU does not see full throttle due to poor adjustment?



D

[Dean]

Partial failure.

I had to use the car for work today due to mitsi being in the garage and no courtesy car and the issue is obvious.

The ecu thinks idle is at about 10% throttle, these makes for a very rough drive as at cruise doing 1600rpm lightly holding the throttle the ecu turns the fuel off, the engine does not like having the fuel turned off at part throttle, i had to drive by accelerating up to speed and letting off the throttle quickly (to close the throttle before the ecu cut the fuel off) to keep things smooth and give the engine mounts a rest, i would then need to let the car coast down to below 1400rpm (below which there is no fuel cutoff) to accelerate again.

if i clock the TPS back to only show idle as the throttle plate closes then there is not enough travel in the throttle to trigger full throttle so................ what to do? abviously i need to get the idle trigger set right but the ECU will never see a full throttle signal which cannot be correct.

D

[Dieselman]

Does the TPS need to report full throttle? Is it possible that the higher load sensing is reported by the MAP sensor and CKP, without reference to the TPS, other than reporting the throttle is wider than xx?

[Dean]

That must be the case Will but why have the ability to register full throttle? the throttle state comes from the ECU after all when viewed on the lexia, why would the ECU be able to distinguish it is at WOT but have that threshold set too high for the sensor to reach with the throttle plate movement available.

Just going to eat dinner and go sort it out though so hopefully i will know why in a minute.

D

[White Exec]

May not be textbook, but (as an experiment) how about increasing the voltage supply to the TPS, so that at max travel it sends a higher signal. Maybe try 9v, instead of the standard 5v - easy to do with a 9v PP3 or w.h.y.
Just an idea. Might prove a point.

Don't our ECUs "learn" and allocate the available sweep of voltages, during the first few miles of driving following disconnection and rebooting? So maybe it doesn't matter what absolute voltages leave the TPS, so long as it's a sweep, which tbe ECU can interpret. Unsure.

[Dean]

OK here is where is stand, Citroen's own manuals clearly state closed throttle plate should read .5v (+/- .1v) and full throttle should give 4.5v
I followed the citroen wiring diagram also and that was a disaster, it just does not work.

I had the TPS and its wiring set up to read as follows, .47v throttle plate closed , 3.9v full throttle. The issue is the ECU calls everything under a .87v signal 'idle' and anything between .88v and 3.89v mid throttle position, anything 3.9v and over is full throttle.

You must have the ECU displaying an Idle status only while the throttle plate is fully closed, if not you have my current problem where it turns the fuel off above 1400rpm and with any TPS voltage below .87v, currently my perfect 40mph cruise speed throttle position produces a voltage of .75v and so cuts the fuel off.

There is no way to get the TPS to read 4.5v at WOT unless it is wired backwards, this gives 4.5v at idle and down to 1.2v at WOT and i have tried using 3 different sensors, two throttle body's and every permutation of wiring possible, you just cannot get those figures Citroen state.

I have changed the wiring and TPS clocking to give a throttle plate closed voltage or .86v so as soon as you touch the throttle the ECU throttle status becomes 'MID' and i can now only achieve a maximum voltage at WOT of 2.95v which means the ECU never gets near a 'FULL' throttle status.

Going for a test drive.......

Chris the ECU does not seam to learn anything, you set the TPS and wire it for Increasing/decreasing voltage with throttle application or a wide or narrow voltage sweep (.47v-4v or .85v-3v and thats it, there are set voltage thresholds programmed into the ECU where it decides it is either IDlE, MID or FULL throttle.

The Citroen manuals seem to be utter BS in thi instance

D