ECU problems.

[RobDorey]

Message for builders using M50 type engines.

I've just had to take the ECU to the repair shop as the engine was running on five.
I found that No.6 wasn't sparking and replaced the coil.
Still not sparking.
Looked on the Nerdnet for info and discovered that if an ignition coil blows, it can take out a circuit in the ECU.
Took the ECU to the ECU doctors and they discovered that this was the case.
£40.00 to test for problems.
Estimate for repair;- £230. (Oh clucking bell).
The choice is breaker yard for an ECU of unknown quality (E36s have a problem where the compartment housing the ECU could fill with water) or bite the bullet.
I bit. Mainly for the 6 month guarantee and peace of mind.
Oh well.

[Patrick]

Ouch! Is your car pre EWS?

[RobDorey]

I gotta plead dumb here and say what's EWS?

[Patrick]

"Electronic Watchdog System" I think stands for. It's the security immobiliser system where you've got a little extra black box that links the ECU & key and they need to match or it won't run at all.

We had do deal with that when we swapped the engine on Richard's daily driver - was quite simple there as his old engine had it as well do all the wiring was in place.

[RobDorey]

I don't think that this one has EWS as it is one of the first M50s (1990).
I don't recall a black box other then a regular BMW immobiliser which was installed later.

[RobDorey]

More problems.
I got the ECU back from the repairers and fitted it complete with new coils.
It ran beautifully on all six for about five minutes and cut out on number six again, then died with a cough.
ECU went back to the repairers. They said that, this time, the ECU had a massive power spike, let all the smoke out and blown up big style, which (in their opinion) leads to a major fault in the cars wiring. Now, I've checked my wiring and can't see anything obvious.
The car was wired using the diagrams on the www.diakom.ru site(http://www.autolib.diakom.ru/CARS2/index.html).

Question is;
Has my car got a fault?
Is the wiring diagram correct?
Are the repairers telling me a load of equine faecal matter?

Has anyone had any wiring problems similar to this?
And has anyone got a reliable wiring diagram other than the www.diakom.ru one?

Due to fiscal embarrassment at the moment, I've had to shelf the car and stop spending cash. So I've plenty of time to solve the puzzle.

[peterux]

Ouch, that sounds expensive!
I don't know anything specific about this ECU but I would start by checking whether you have grounded any of the 'unused' outputs by mistake. Also check that you have got your engine and ECU grounds all connected correctly.

good luck,
Peter

[MartinClan]

Originally Posted by RobDorey

They said that, this time, the ECU had a massive power spike, let all the smoke out and blown up big style, which (in their opinion) leads to a major fault in the cars wiring.

Very difficult one this. Modern car electronics are very robust - I am surprised that a fault with an ignition coil can blow the ECU. The output that drives the coils must be short and open circuit protected, and protected against spikes.

The only thing I can think of that would really give the ECU a hard time was if somehow the HT had found its way into it.

It's also strange that the same fault has happened twice. How reputable is your "ECU Doctor" They could have made a crap repair which has resulted in the second failure.

What I would do.

Double check my wiring, not only physically but with a meter to make sure you have the right volts on the right pins.

Try and find a second hand ECU from ebay perhaps?

How long was the engine/car running before this happened? If it has been running OK for some time that eliminates any wiring errors on your side...

Robin

[Patrick]

What year is it, I may be able to help with wiring diagrams

[RobDorey]

I drove the donor home just over two years ago and, although it had been parked up for over two years, started with jump-leads and ran okay on (I presume) all six.

After stripping the car, the ECU was tucked away safe with the ABS ECU.

I followed the wiring diagrams on www.diakom.ru (one wire at a time), and wired it as per BMW with as many donor parts as possible using the fuse box (except for the trip computer, interior lights, etc). I haven't encountered any problems until now (the ABS light blinks for a micro second when you turn on the ignition and stays out, but had a problem where it came on when you drove above 5mph. But even that seems to have cured itself and stays out when driving).
The car started very easily for the first time, although I couldn't tell then if it run on all six without an exhaust, it's been starting and running with ease.
It was only when the exhaust was fitted that I noticed it was running on five, and tracked the problem to the blown coil.
I'm going to get a friend of mine to have a look see, because a fresh pair of eyes may spot something silly.
The donor was a 1990 e36 2.5 saloon with about 120,000 on the clock.
The trouble at the moment is that lack of money being a bit of a problem being between jobs just now, and the fact that this problem has dented my confidence a tad, has left me feeling lower that a snake's belly in a wheel rut.

[Patrick]

{removed}
Let me know when you have them so I can take them off again

[RobDorey]

Junno, I've just had a look at the log book for the donor and discovered that it was first registered 2nd May 1991 and not 1990 as I thought.

Thank you Patrick for the PDF file.
I'll check it the car against it and get back to yawl.

Rob.

[Patrick]

There isn't a 1991 file for the E36 either, but there is a for the Z3.

[RobDorey]

Patrick,

Looking at the cover sheet of the PDF, it covers vehicles from 4/91 to 8/92.
So I it looks like I have an early E36.
Anyway, Task No1 is complete.
I've spend the afternoon (with a large whisky), using Excel, writing down the pin connections from the BMW wiring diagram and the one I used from Diakom.ru.
The good news is that they agree with each other.
To the casual observer, this would seem a futile undertaking and the result would seem obvious but I'm gritting my teeth and leaving no stone unturned.
The next task is (with my electronics genius friend) to painstakingly pick out the ECU wires, one by one to see if I suffered from temporary colour blindness.
I get back to you on this one.

[peterux]

Rob, always check for obvious things first!
For the circuitry to 'blow up' means that it has experienced an unusually high voltage or an abnormal high current.
I'd start by checking the ECU is grounded to the chassis.
Maybe if it's not it will be floating up to the high voltge levels and then discharging to earth.
Are any of your earth connetions loose or intermittant?
If bolting to the chassis, did you remove the powder coating where the earth is bolted down?

If that's not it, look for any wires that could be shorting to the metal chassis.

good luck

Peter

[RobDorey]

Peter,

Interesting that you say about grounding.
The ECU, on the donor car was held in a sort of 'sprung-loaded' bracket, which I'll used. The bracket is the only way the ECU can earth.
I wonder if I should have grounded the ECU chassis and not trusted to the bracket for earthing.
I'll check this and (for belt and braces) add an earth tag to the next ECU (When I procure one).

[RobDorey]

Okay,
Task No.2 is complete.
I've checked the wiring against the diagram and it's all correct with no problems.
So tomorrow, I will tackle the ECU repairers and throw the ball back.

I'll get back to you on this one.

[RobDorey]

As I suspected, the repairers don't want to know.

The old ECU either had a fault that the repairers didn't spot (unlikely) or (the current favorite, after a talk with an electronics genius pal of mine) the stuff they dip the ECU in to remove the lacquer from the circuit board is old and has metal particles in it which can cause a short.
But they're not going to admit that are they.

I suppose this is one of the troubles you face when building, to another's point of view, an unknown quantity.

If I were to have this trouble with a standard, un-modified car they would be accountable. But there you are.

So I am now in possession of another ECU from Quarry Motors (BMW breakers) for the sum of £80.

Using Peter's suggestion, I've Earthed the body of the ECU, checked the wiring and linked all the coils together (they were earthed in two sets of three from standard and now have two earth braids feeding six coils).

The car now runs sweetly on all six.

I'm building confidence with every start up.

[Patrick]

Glad you got a solution sorted