Suddenly I have a computer and a misfire!

[MikeO]

Filled up with petrol this morning and two odd things happened.

Firstly I noticed that now instead of having outside temp displayed I have miles to re-fuelling - which is odd since I don't have a computer fitted and, as there's no stalk to control it, no way to scroll it back to temp.

Presumably the software is on all the cars but isn't activated without the stalk. (It's a '98 996 3.4)

Secondly, and much more concerning is that I've had a major misfire ever since. Peculiar co-incidence but actually I think it's unrelated, it's not like it's changed to a different ecu map or something as it's too inconsistent.

I've just phoned the petrol station and they're saying that no-one else has called with any problems. I had let the level drop further than it's ever been before and I suspect I've stirred up some muck from the bottom of the tank.

Went for a run to see what happened if warmed it through - had a patch of suddenly getting a lot worse (and the emissions warning light came on and stuck on at this point). But having stopped and restarted it seemed a lot better as I limped home.

If it is muck what's the chance of it clearing itself? Not sure whether I need to get it in the garage first thing in the morning or whether later in the week will suffice. I'm going to take it for another run later to see whether it has cleared itself.

Any thoughts on either issue??

Apologies if anyone has also seen this on Pistonheads but I'm not getting a lot of joy there.

 

[Richard_Hamilton]

The OBC is built in to the instrument cluster, but not activated at the factory unless the stalk is fitted (as an option). The cluster can be coded for OBC afterwards, and this causes the outside air temperature to display (the default setting). Someone has obviously coded it after it left the factory. It is strange that it has changed to the 'range' setting of it's own free will - it must have had some kind of blip or power loss to the cluster. You won't get the OAT reading back without fitting a stalk or simple switch, as it stays on the setting last used.

As for the misfire - I seem to recall yours is pre-eGas (M620 option code), so you could try resetting the DME by disconnecting the battery for a couple of minutes. Don't forget to switch the ignition on first, to stop the alarm siren going off. If it doesn't cure it, then you need to get the fault codes read.

Personally, I think the two are likely to be related, but that's just a hunch.

 

[MikeO]

Turned out to be a ignition coil on cylinder 6.

I am developing a hot start problem that can cause a momentary loss of electrics - although I didn't notice this yesterday (usually it sets the alarm off) I suspect this is what caused the computer blip.