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325 ROUGH RUNNING AFTER THERMOSTAT CHANGE!

PostPosted: Sun Feb 14, 2010 8:39 pm
by cbn2000
I need some help with this one,

I've just changed a on my 91 325. Running sweet beforehand (but not reaching full temp). After re-fitting the thermostat housing, I tried starting, but the engine would barely fire. I then noticed a black wire that should fit behind a 10mm housing bolt that I'd left off. I touched this against the engine (ignition on) and noticed a spark on contact (wire runs to plastic injector/ignition coil wiring housing). I re-fitted the wire. Upon re-start, engine started but sounded like it was running on 4 or 5 cylinders. It now runs so rough it's undriveable. I've checked that no obvious cables have been disturbed - that one wire is the only significant thing I touched! - much appreciated if anyone can help.

Re: 325 ROUGH RUNNING AFTER THERMOSTAT CHANGE!

PostPosted: Mon Feb 15, 2010 8:08 pm
by 96_323
When you started the car without the earthing wire you would of blown several fuses.
Is there any of the other electrics in the car not working? I.E. Windows, sunroof, interior lights?

Re: 325 ROUGH RUNNING AFTER THERMOSTAT CHANGE!

PostPosted: Wed Feb 17, 2010 6:47 pm
by cbn2000
Thanks for the reply. All other electrics are fine, checked fuse box - all ok. Disconnected battery and re-connected, no improvement. I've been informed by a BMW garage that the wire in question is the main engine management earth, and that I may have damage the ECU. I'm not yet 100% convinced by this. Still stuck, I think I'll end up plugging in to a diagnostics check to understand the problem.

Re: 325 ROUGH RUNNING AFTER THERMOSTAT CHANGE!

PostPosted: Wed Feb 17, 2010 8:11 pm
by 96_323
They are right about it been the ECU earthing wire unfortunately.
Try the diagnostics scan and let us know how you get on.

Re: 325 ROUGH RUNNING AFTER THERMOSTAT CHANGE!

PostPosted: Sun Feb 21, 2010 10:26 pm
by cbn2000
[quote="96_323"]They are right about it been the ECU earthing wire unfortunately.
Try the diagnostics scan and let us know how you get on.
REMOVED ECU, TOOK A LOOK INSIDE - HORRIBLE SMELL + EVIDENCE OF BURNING, I WAS DELIGHTED WITH THE STRONG EVIDENCE I HAD FOUND THE PROBLEM! GOT HOLD OF ANOTHER ECU FOR £10 - SAME M50 ENGINE LISTING, AND SAME MOTRONIC VERSION - THE ONLY DIFFERENCE BEING THE SERIAL NUMBER ENDED 402 INSTEAD OF 403. FITTED IN CAR, NOW IT RUNS BETTER, BUT STILL ROUGH. DO YOU THINK THE SUBLTE ECU NUMBER DIFFERENCE IS THE LIKELY PROBLEM - OR THAT THERE IS DAMAGE TO OTHER ELCTRONICS FROM THE INITIAL PROB. I'D BE THANKFUL FOR YOUR OPINION.