Xsara multiplex AL4 auto - weird converter lockup fault

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Haakon
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Xsara multiplex AL4 auto - weird converter lockup fault

Post by Haakon »

Hi there - hoping some gurus in europe can help here. Australian experience with PSA cars is minimal.

I have a 2002 Xsara automatic - EW10 engine, AL4 transmission, multiplex.

My fault is with the transmission. It will behave well all day long around town, with shifts and torque converter lockup functioning properly.

But if it spends any more than 5-10 minutes on a freeway, the torque converter lockup will disengage. It does not go into limp. If I pull over, turn the car off and restart, it is all normal again for another 5-10 minutes.

The transmission has been completely rebuilt from scratch once, and then completely replaced with another totally reconditioned transmission when the first rebuild failed to resolve the issue. It has been thought that slippage of the converter is making the transmission ECU unlock it.

With the problem remaining, I am looking towards less obvious possible faults and the BSi is one. Is it possible it has a fault thats affecting the transmission behaviour?

Or should I be looking at the transmission ECU itself? All have tested as ok with the PSA diagnostic equipment, as have things like brake light switches etc.

It had a new converter both times, and a third new one between transmissions. Converter was certainly a candidate, as the original one was pretty toasted with burnt a clutch.

Fluid level correct, new LT1771 every time. Brand new Valeo large coolers fitted every time (its not that hot here though at the moment, and heat is not a factor). Counters reset along with software updates.


Any help most appreciated !!
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Re: Xsara multiplex AL4 auto - weird converter lockup fault

Post by wheeler »

Haakon wrote:With the problem remaining, I am looking towards less obvious possible faults and the BSi is one. Is it possible it has a fault thats affecting the transmission behaviour?
I would be very surprised at a BSI causing this fault as it has very little to do with the under bonnet side of things.
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Post by CitroJim »

Welcome to the forum haakon :D

Although I'm not in any way au-fait with a multiplexed Xsara, I'd be inclined to say the problem was more with the engine ECU giving a duff signal to the autobox ECU.

The torque converter should, once in second gear or above, only unlock when there's a demand placed on the engine for rapid accelleration. If the AL4 behaves anything like the 4HP20 in my V6 then it will be keen to lock up and stay locked as soon as possible. I see and feel mine unlocking briefly when a demand is made for acceleration and then locking again.

Therefore, I wonder if your gearbox ECU is receiving an erroneous signal telling it that rapid acceleration is required and to slip the torque convertor please?

Does the 'box correctly kick-down if the accellerator is floored?

The lock-up clutch is actuated by an electrovalve that reverses the flow of oil through the torque converter. It is possible that low oil pressure or the wrong grade of fluid could possibly cause a slip but you've very clearly ruled that one out.

Rather than mechanical, I'd say the problem was electronic in origin. One immediate thought is whether or not the throttle pot is good. A bit of intermittency here could give misleading signals to the ECU informing it of an acceleration demand when really there is none. How this signal is relayed to the autobox ECU and how multiplexing might have an effect is not known though...
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Haakon
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Post by Haakon »

Cheers guys.

It does kick down, normally for a french auto (ie with a thump and lurch) when its supposed to.

The throttle TPS could also relate I suppose to the fact that sometimes its shifts are buttery smooth, with just the right amount amount of "firmness", and other times there is a distinct shock internally - not enough to make the car jerk, but you can feel the internal shocks as drive is taken up abruptly. Its usually the 1-2 shift.

Any hot tips on testing? Assuming Lexia here...


It also has another thing I noticed, which I'm not sure if its a normal characteristic - relating to the 2-3 change. It feels like there is a delay in lockup once 3rd is grabbed. It results in an odd "pause" in acceleration - it grabs 3rd with the normal rev drop from 2nd, then revs go up with the "rubber band CVT" type progress, then revs drop again or hold steady as road speed catches up. Then I'm usually at the point of grabbing 4th, which it does normally.

I've not any experience with other AL4s, so cant tell. It almost feels like it slips in 3rd momentarily, or doesn't lockup straight away, but its almost too subtle for me to tell if its wrong.

I'm also going to ask them if they have been checking temperature sensors (assuming so) on the off chance an erroneous signal is forcing the cold weather law to be engaged (ie unlocked converter).
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Post by addo »

Wie geht, mate?

I think it's a fairly "dumb" ECU on the box; it probably can retard injection by shortening injector dwell times under less ideal kickdown, to avoid internal damage but otherwise pretty sure it's self-contained.

Actual driving with an intelligent passenger watching the parameters would be one way to detect what's happening. You can see in and out speeds, electrovalve status (all, binary), fluid temp.

In terms of the kickdown thump, that's a specialty of the rebuilders so far as I can tell. :roll: Mine is these days making a sort of dry bushing squeal under hard pedalling, which is probably something on the input side starting to fail (at 82K-odd)...
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Post by Haakon »

Howdy ;) How's things? It's kick down certainly no worse than the original reno AR4 and MJ3 autos I have...

Ah well. Back it goes on a tow truck on Monday, and they can continue playing with it for a couple of weeks while I'm in the US watching space shuttles :)

I suspect though I'm not far off finding the assorted ecu and throttle bodies at wreckers and just swapping bits until it works...
Last edited by Haakon on 19 Feb 2011, 09:38, edited 1 time in total.
Haakon
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Post by Haakon »

Who knows if an EW10 equipped C5 would be a suitable engine and trans ecu donor...?
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Post by addo »

You'd probably need a Xsara as the BSI is coded into the engine ECU and so far as I understand things, can't be re-written. Trans ECU alone might be OK to swap.
Haakon
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Post by Haakon »

Still no joy on this thing...

The transmission builder are basically pulling the pin on it, and are convinced its a fault somewhere else in the car.

Its had two transmission built from scratch, several torque converters, a few valve assemblies and countless hours.

They have checked continuity on every wire in the transmission looms, tried another trans ECU.

This transmission has new everything on it - all sensor, multifunction switch, the works.

They have had all the diagnostic equipment hanging off it, all showing perfect data. And it continues to not put up a fault code or show any abnormal electrical or pressure readings, even as the lockup fails before their eyes!!

The next step is start looking seriously at the multiplex system and engine management systems. Its been pretty well decided its a control issue, and it might be as a result of the transmission control systems responding to odd signals from elsewhere in the car.


Anyone know where I can get a known good engine ECU/BSI pair for a 2002 Xsara 2 litre automatic (EW10 engine)...? I might try another throttle body/TOS assembly as well.
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