BMW Repair: Backfire, bmw 318is coupe, bmw 318is

Question
Hi Rob,
Wonder if you can help? I own a BMW 318is coupe, 1992, M42 engine, that has just recently suffered a backfire. The engineer on the case has said that it's taken the coils out (£220 to replace). After replacing the coil pack, he told me he wasn't getting a spark from no.4, so a new set of leads were installed. He then told me, the new leads and coil pack haven't solved the problem, and so it was on the diagnostics at the local BMW dealership. It has now been decided that the ecu is at fault and needs to be replaced! Question is, would a new ecu solve the problem and what causes the backfire in the first place? I'm quickly losing my mind and would appreciate any advice you could give me.
Thank you - Mark.

Answer
Hiya,

ECU's can develop a fault for any number of reasons or sometimes, seemingly none at all. Water/moisture ingress and the malfunction of another circuit can be the cause.
Your best option would be to see if you can borrow another ECU to test the car with. Hopefully you don't fry that one!
You can open your ecu to check the printed circuit for any signs of burning (you should smell it the moment you open the ecu) by prying open the tabs on the ecu and opening it very, very carefuly and (once checked) closing it just as carefully.
I assume the cam position sensor has been checked?

let me know how it goes

Regards

Rob