Why am I asking all these silly questions?

Stempy · Post by **Stempy** » 08 Jun 2004, 02:22

Well, it's because in the quest to cure the 'misfire' that I am experiencing I have had the thing on a citroen elit analyser which showed up absolutely nothing. I've also swapped the coil pack and no difference.
The only thing the analyser said was intermittent O2 fault and intermittent load fault which the guy said was irrelevant.
I think it's going to come down to willy nilly replacement of sensors and hope one of them cures it.[:(]

AndersDK · Post by **AndersDK** » 08 Jun 2004, 02:34

What car IS it [:p]
- and how does it misfire ?
-during acceleration
-during coasting
-during load (at highway speeds)

Stempy · Post by **Stempy** » 08 Jun 2004, 02:45

Xantia V6 24v. I'm not even sure if it's a misfire in the true sense of the word. The effect is jerky acceleration. When stone cold it runs how you would expect. Then, as it starts to warm the acceleration becomes erratic and you can feel it hesitating. Once you get going and up to cruising speed it seems to run fine at constant throttle.
Also if you have been stuck in traffic for a while and it gets fully hot it seems to run best of all, but after a long stretch of motorway driving, when you slow for a junction or roundabout the hesitation comes back as you accelerat away. Sometimes after braking almost to a stop, when putting your foot down to pull away again it almost dies then the power comes in with a bang.

AndersDK · Post by **AndersDK** » 08 Jun 2004, 03:07

tough one ...
If an earlier carb engine, i'd say the accelerator pump hesitating, momentarily leaning the engine.
This points to fluctuations in the fuel pressure on injection systems.
Over riching the engine may give similar symptoms, but then you should occasionally have a backfire on the intake.
The ignition vacuum advance mechanism/sensor could (mis-) behave like this too, simply by having any hose connection split or oil contaminated, even a split diaphragm.
An ignition problem would more than likely come in constantly, at a certain engine temp, so this I rule out.

Stempy · Post by **Stempy** » 08 Jun 2004, 03:30

To add to the misery, the auto adaptive gearbox ecu and the engine management ecu have little chats with each other, and if the gearbox ecu is unhappy for any reason it can tell the engine ecu to back off the power a bit, so it could even be gearbox related.

paranoid · Post by **paranoid** » 08 Jun 2004, 03:47

Where I used to work we had 6 cavalier GSi's with that sort of problem and a couple of belmont CD's (yuk) These syptoms only emerged after about a year, tried everything dealer software updates the lot all no good.
Out of desperation had them fitted with superchips (about £300 each) that cured them instantly from then on they really were amazing to drive (even the belmonts)this might be worth a try.
Try taking it to a purely Electrics/injection specialist they always seemed 200% better than the dealers

AndersDK · Post by **AndersDK** » 08 Jun 2004, 03:54

When things are a bit too complicated, I always tends to shout commands to operators around any industrial machinery at fault !
As an engineer, you basically <i>have</i> to get your self decent working conditions. It wont help you if you're tracing faults at the can filler machinery, and then operators keeps hitting the emergency stops because of faulty cans at end of the production line ...
meaning : <i>must</i> be a way of cutting off that adaptive gearbox control. Cant be right that an adaptive gearbox ECU would stop engine, if you take out the gearbox ECU fuse, or rip it's multiplug ...
You simply have too many variables right now to get a fair chance !

Stempy · Post by **Stempy** » 08 Jun 2004, 04:02

Spanking Idea Anders. I would assume that there is an emergency back up hydraulic mode in the gearbox in case of failure of the electronic control, I will certainly look into it.
Will have to leave the superchips idea as a last resort, I dont think thay even do one for a Xantia.

paranoid · Post by **paranoid** » 08 Jun 2004, 04:07

To there credit they will try and map anything for the same price as off the shelf stuff, they really will put themselves out for you

xantiav6 · Post by **xantiav6** » 08 Jun 2004, 12:02

How long can the misfire be sustained? Is it long enough for an exhaust gas analyser to get a reading?
On the powerchip question, there appears to be a tuning chip available from several vendors in Europe e.g
http://users.otenet.gr/~mwise/power-tuning/citroen.html
It is possible that the software map is marginally unstable at some point and gives these symptoms due to engine wear. I know of an example of this on mid 80s 3.6 litre Jaguar engines.
Mike

Stempy · Post by **Stempy** » 08 Jun 2004, 12:30

To get a true idea of what's happening I think it would need to go on a rolling road as the problem doesn't really show when revving the engine at a standstill.

Stempy · Post by **Stempy** » 08 Jun 2004, 23:51

Well thanks to the stroke of genius by Anders I think I can eliminate any problem with the engine itself,and am now pointing the finger at the gearbox.
I pulled the fuse that supplies the autobox ecu this morning. The box duly locked itself into third gear and although obviously sluggish, there wasn't a hint of hesitation, stutter, misfire or anything, the engine ran smothly through the entire rev range from cold to hot.
So now I have to figure out exactly how much interaction there is between the ecu's and whether the gearbox ecu is telling the engine to retard the ignition or whether the stuttering comes from the hydraulics of the gearbox going into spasms.