Deaf and Dumb Xantia

tim leech · Unread post by **tim leech** » 04 Sep 2010, 21:16

My 94 Xantia 1.8i 8v has had a problem for the past 5 years that I have spent a small fortune on trying to get it right, today after Sir Jim of Eastman plugged his lexia into it which shows up that the ECU doesn't know when the engine is running or not (getting no signal), a so the there's no advance, hence the engine is running very retarded, running VERY rich and using lots of fuel and being very slow. The lexia didnt found no revs, nor advance nor a signal from the stepamotor (the rev counter works fine)

The ECU is not at fault as its been replaced already by a good known one.

Just a quick question if anyone has come accross this before, It could be a bad connection or broken wire, but before I start spending even more money on it with an auto electrician I thought I would ask.

Thanks!

Unread post by **xantia_v6** » 04 Sep 2010, 21:23

It sounds a bit odd to me. If the ECU does not know the engine is turning, why does it ever fire the injectors?

tim leech · Unread post by **tim leech** » 04 Sep 2010, 21:48

xantia_v6 wrote:It sounds a bit odd to me. If the ECU does not know the engine is turning, why does it ever fire the injectors?

You got me on that one, maybe Jim can explain better.

Unread post by **CitroJim** » 04 Sep 2010, 22:47

tim leech wrote: You got me on that one, maybe Jim can explain better.

Got me too

I've been reading the diagrams and the tacho is driven by the ECU...

But the Lexia clearly showed no rpm readings and 0 degrees advance...

I'll go to bed and think on that one.

Bring it to Stratford Tim... Or come to to see me one weekend...

I'm really confused now...

tim leech · Unread post by **tim leech** » 04 Sep 2010, 22:55

ok jim.

Unread post by **xantia_v6** » 05 Sep 2010, 07:30

Does the fuel pump continue to run with the ignition on and the engine stalled?

Unread post by **CitroJim** » 05 Sep 2010, 07:31

I've had a night to mull and cogitate this one and there's something very funny going on.

Lexia reports an L6A Engine on global test and I understand this to be the non-cat XU7. The engine should in fact be the LFZ with the cat.

So, is, for some reason, the ECU misreporting and the lack of timing and tacho a complete red herring?

I'm suspecting so now but it just deepens the mystery. I want to see this car again at my workshop Tim, where I can properly look at it with all my kit around me.

fancy a trip to Newport at some point Tim?

DickieG · Unread post by **DickieG** » 05 Sep 2010, 08:03

If Tim's at the CXM today or maybe Stratford next week I have a couple of other diagnostic tools in addition to Lexia, one I know where you can choose what software the ecu will be using, mind you you can normally do the same on Lexia if you don't use the global test.

I'd suspect that its a non communication error between the ecu and Lexia.

DickieG · Unread post by **DickieG** » 05 Sep 2010, 08:08

I think I may have found out the cause, Info Rapid 1/77 refers to just such a problem which is caused by incorrect earthing of pin 25 on the ECU, remedy is to remove the earth connection on pin 25.

Edit; In addition to non communication between the diagnostic tool/failing emission tests, pin 25 should only be connected on non cat L6A engines.

citronut · Unread post by **citronut** » 05 Sep 2010, 08:46

so it cant be something to do with the ECU being replaced?????

maybe not quite the right one

regards malcolm

tim leech · Unread post by **tim leech** » 05 Sep 2010, 09:54

Thanks Guys,

Malcolm it was just the same before the ECU was replaced, I checked the two ecus side by side to ensure they were compatible.

I can bring the Xania to stratford Jim then always on to yours afterwards if you want?

Tim.

dnsey · Unread post by **dnsey** » 05 Sep 2010, 10:13

I checked the two ecus side by side to ensure they were compatible.

Visual similarity isn't a conclusive test, though. You'd have to read the ROM contents to ensure they were really identical.

tim leech · Unread post by **tim leech** » 05 Sep 2010, 12:14

I think I still have the old one, either way it made no difference to the way it ran when I swopped them over except the engine check lamp doesnt come on all the time now which it did before, it was from the same model, engine, transmission and year.

Unread post by **Old-Guy** » 05 Sep 2010, 17:30

Right, so neither ECU is at fault - unless both have the same hardware fault which is not that rare.

But chaps, let's not forget that the software in the ECUs and in the Lexia was written by fallible (and often lazy) programmers (I know - I spent a large chunk of my life writing all sorts of software!)

So, it's as well to never ever completely believe diagnostic messages - sometimes you'll have a set of circumstances that the software designer didn't think of (or couldn't be bothered to deal with) so you can get totally misleading messages (even a set of apparently consistent messages). I've experienced this from both sides of the fence!

Funnily enough, my immediate thought was "dodgy earth often causes weird effects". If the technological solution doesn't work, - go back to first principles and start checking the data at source.

DickieG · Unread post by **DickieG** » 05 Sep 2010, 20:21

Lexia will search for the relevant software for whatever it detects with regard to ECU's and the attached wiring loom, now bear in mind that the additional earth on pin 25 should only be used on L6A engines so when Lexia searches it detects the additional earth and then applies software relevant to L6A but that software is not compatible for a 1.8 with a cat (LFZ) hence Lexia cannot then communicate with the ECU.

Citroën established that the looms fitted to a batch of these car's was wrong and issued an "Info rapid" (service bulletin) so why look a gift horse in the mouth and waste further time and money looking for the end of a rainbow when numerous items have already been exchanged without success when a brief trial of disconnecting pin 25 on the ECU may sort it, why try and complicate matters further? Am I missing something here?