E30 Zone

Hello,

I wonder if anyone can help me. I have a 1991 320i which I love very much. Recently I have a new issue which no garage has been able to fix.

I get to 70mph on the motorway and after about an hour, if I want to take over, anything passed 75 and I backfire.
The rev counter drops just before it fires which I'm lead to believe is a ignition issue?
Also I've noticed that the temp gauge goes a bit odd and flicks and fluctuates around the backfire.

All other times the temp gauge is good and below a quarter.

Could anybody shed some light, maybe experienced similar?

Thanks

Emma

If your temp gauge is always below a quarter, then your car is overcooling, probably due to a duff thermostat.

This means your car never gets up to operating temp, so the engine is constantly overfuelling it in an attempt to warm it up, which in turn is causing the backfire.

Pull out a spark plug; I expect it's caked in soot.

Coil or Dizzy cap breaking down ?

Thanks for the replies.

I'll check tomorrow with the sparks and thanks for the info on the temp gauge, the garages didn't look at this, I'll get that checked asap.

Dizzy cap? You mean the distributor cap needs replacing? My symptoms do sound similar to this issue.

If the tacho. needle drops out as you say, you have an electrical fault in the management system which is killing the sparks, but allowing the injectors to continue to run.
Unburnt fuel mixture passes into the exhaust system, and is ignited when the sparks return.
If the tacho. drops out, then the problem will be in the ECU or before it - it won't be coil, plugs, leads or distributor related.
My two prime suspects would be the DME relay or the engine ECU itself. Any idea what the garages have tried/replaced?
There may or may not be a problem with the engine running temperature (it should be just past the 1/4 mark), but this is a separate problem.

Hey Brian,

Thanks and very interesting that you would say its electrical.

I had a huge electrical issue before where I would be at 70mph on the motorway and the engine would just cut out, i'd lose power instantly, it felt like the car was breaking. Sometimes I was fortunate that it would come to life, but it became very frequent all of a sudden.
Sometimes the engine would just not turn over. I had many call outs with the AA and they would spray into the carburettor, sometimes this worked, but it got frustrating as I would be towed into a garage and they would phone me after a few days and say they had to issues with the car at all. I'd take it away and hey presto it would die again.

Its been to a garage near Twickenham one in Crouch end, many AA mechanics and finally I took it to a mechanic I trust in Tottenham who is great and always fixes my issues. He only works on BMW classics and this is my second car.

He fixed it, it was electrical and was a large job.

But yes, a while after this the backfire started.

Am I to believe its the same issue or a new one? If you think its the DME relay or the engine ECU, would you recommend I take the car back to my usual garage or can you recommend a place I should go to instead?
I don't mind going on a mission I just want to get her fixed!