Citroen XM Forum

Dean wrote:............Including a new ECU, the new ECU was worse than the existing one but probably due to the incorrectly wired TPS...

I know,i know that you allready tried different ecu.Just saying that it could be at fault too.
Something isn't right here.

You are right, something is not as it should be but it is running properly now so far as i can tell.

I have the correct voltage to the TPS with a good ground path and continuity through the ECU signal wire
I cannot get the correct min / max voltage output back to the ECU or the correct range of voltage

I can get the correct voltage over the full range but it works backwards so starts with the thottle plate closed showing 4.5v and 'FULL' throttle with .4?v 'IDLE' at full throttle.

The throttle plate is correctly fitted, the TPS can only be fitted one way, wiring it differently will either (as stated above) will give incorrect range or limits but in the correct direction (increase voltage with throttle application.

D

Just went and checked the TPS voltages on my 1992 V6 auto - my engine is a S6A (no oxygen sensor, hopefully shouldn't make any difference). At idle it is 0.52v, 2.5v mid throttle and 4.52v at full throttle - pretty much perfect.

One interesting / strange thing I did notice is that it switches from "mid" to "full" at anything above 2v - this occurs somewhere around 1/2 throttle (bit hard to tell). I would have thought that would switch to "full" with a little more throttle than that - it would be interesting to see if other V6s behave in the same way. I probably wouldn't worry too much about the voltage if it reports the throttle position correctly.

I do notice that mine reports neutral / drive backwards - in park or neutral it says "drive" and in reverse or drive it says "neutral". I assume yours works the other way around? I might have to look into that.

Couldn't resist, had to play again, it's bugging me

Put the Manual ECU on tonight and the idle was way too low still so i wired the TPS back in the same as I previously had it giving idle voltage or .49v and max voltage of 3.9v
This gave the correct idle state with throttle plate closed but the throttle had to be opened a fair bit before changing to 'MID' status. Started the car and idle speed was spot on, took it for a drive and I have hesitation mid range again and a jerky on/off throttle transition down to the throttle plate opening too far before the ECU selects 'MID' throttle state, this is the problem I had yesterday which I resolved by rewiring the TPS which gave a lower maximum voltage but a higher minimum voltage so the ECU would switch from 'IDLE' to 'MID' as soon as you move the throttle and drive ok.

I plugged the Auto ECU back in and looked at the live data, this ECU still displayed the same voltages (.49v throttle closed and 3.9v WOT) but the important bit is that the ECU state would switch from Idle to mid at .60v, this was new, previously it was making the change in mode at .80v ish, i clocked the TPS to read .58v with closed throttle and as soon as it was touched the ECU would display 'MID' throttle. I've solved it! but not sure how.

Then, messing around I accidentally let the bare TPS wires touch and the ECU reverted to the middle of the road 2.5v and 'MID' status which is normal when it see's a fault, I separated the wires again and now the ECU 'IDLE' 'MID' status threshold is .70v dammit.

Tried unplugging the ECU and doing other things but it won't change now, i need to get the ECU to recognise the switching threshold between idle and mid throttle as being somewhere between .50v and .60v

Sooooo the ECU can obviously learn the idle thresholds at least, trouble is what did i do to get it to learn?, and don't say drive it, I covered 70 miles yesterday and it wasn't having any of it, the ECU would only accept .80v as the idle/mid threshold, there has only been change after unplugging the ECU this evening, i tried this again but it made no difference, it would not change the switching threshold.

D

JD01JD

Thank you for that, my Auto sign works perfectly yes, not sure why that would be back to front?
Your voltage is interesting, my sensor (if removed) will read .22v to 4.29v, all 3 sensors i have do that.
I can get mine to read 4.15v at WOT operated by hand directly on the throttle but operated on the pedal i can only get a maximum of 3.9v unless you really stamp on the throttle pedal so the issue is not insufficient throttle plate travel.

I noticed the manual ECU has a much higher 'FULL' throttle trigger point voltage than the Auto ECU does as well.

The manual ECU also cuts fuel on a trailing throttle, not sure where i got the idea it does not from.

D

Does the ECU need to be told the idle and WOT throttle pot voltages, via a setting process?

Try IGN on, press the pedal to the floor, hold for 10, then release the pedal.

On some cars you would need to calibrate TPS sensor doing that,but i think that XM is not among them.
I replaced it on 2.0i and it was just plug & play.
I just reset ecu by disconnecting negative battery cable for 10-15min just in case.

I was sure that was the case, the XM is too old for that sort of thing but why does the mode thresholds change? i've tried to get it to do it again but it won't.......

D

Dieselman wrote:Does the ECU need to be told the idle and WOT throttle pot voltages, via a setting process?
Try IGN on, press the pedal to the floor, hold for 10, then release the pedal.

Are there not some manual pages which would confirm this?

If the ECU is not able to learn the voltages offered by the TPS, but needs a set of specified idle/WOT voltages, I can't understand why you are reluctant to ensure that these are available - by upping the TPS supply voltage.

If you don't take a logical approach to this, you could go round in circles for ever.

I don't because the idle voltage is correct to spec at .5v, the trouble is the ECU does not recognise this as idle when according to all info I have it should.
The WOT is too low by .6v but if I increase the voltage to the sensor this will also raise the idle voltage too and I will still have the same problem at the other end of the throttle travel.

I need to find and cure the root of the problem, whatever it may be.

I will look through the TPS stuff John posted in Matthews thread later to see if I missed anything.

D