E30 m50b25 fries ecu's.....

Mon Aug 24, 2015 7:20 am

Hi forum,

So, as the headline says. My car goes through ecus like others are changing underwear.

Brief info on the car:

E30 325i with m50b25tu engine, I made for track and hill climb usage. It has done two ecus now and it happens when I turn off the car on the ignition, fuel pump then master and then want to turn it back on again let's say 15 sec later.

I have now begun to run through the wiring loom, changing all relays I have fitted to ones with diodes over the coil(is this necessary?) moved the fuel pump relay back to be controlled by the ecu and not my fancy racing car switch.... So making it as standard as possible.

Does anybody have any ideas on what could cause this and are all my ecus done or is there a way to control/fix the fried ecus? The ecu is the red label one.

Help!!!!

Mon Aug 24, 2015 7:56 am

Could be a bad earth.

Perhaps try using a wiring diagram to determine which of the ECU pins should be earthed, then check for continuity between each of these and chassis ground.

Mon Aug 24, 2015 8:01 am

Hi,

Done that already and that's all good:)

Mon Aug 24, 2015 9:16 am

It won't be the kill switch or separate fuel pump switches, I've done plenty of E36 racers like this and never had a problem with ECU's going down

Mon Aug 24, 2015 9:32 am

It could be that. There was no relay in the fuel pump and O2 preheat socket. I have re-established that to make it standard again. The previous owner did the engine swap so don't know what has been or not been done.

Mon Aug 24, 2015 1:13 pm

What part of the ECU is failing? that will say a lot about where the fault lies.

How do you know the ECUs are fried?

Mon Aug 24, 2015 1:15 pm

Well, good question. I don't know if the ecu is 100% dead. But there is voltage at the injectors and coils but no signal if that makes sense? No spark and fuel but they get voltage. Change ecu and it works again.

Mon Aug 24, 2015 3:00 pm

Check that the battery is not being overcharged; with the engine running, you should see a voltage reading across the battery of around 14 Volts.

Mon Aug 24, 2015 3:09 pm

13.4v so should be okay.

I was suspecting cheap relays and maybe missing ground through fuel pump relay etc???

Fri Aug 28, 2015 8:05 pm

So there is voltage to the injectors and coils but the ECU is not earthing them out to fire them?

Are all the ECU earths ok?

Are your coils earthed properly? There will be residual charge in them that will have to go somewhere when the ignition is switched off.

Sat Aug 29, 2015 6:30 am

Yes exactly.

I checked that I got continuity between the ecu earths and earth and that was all okay. There was a few that didn't have continuity but there was no fuel relay and O2 sensor heating relay which I have now established again. Was taken away from the previous owner.

I'm in the process of making sure the loom is as standard as possible so will go over I again to make sure all earths are there. Just seems like a lottery every time I turn the car off, will it start again.

At the last event I was, I popped the car I 5th and stalled it to turn the engine off, the ignition then the master. No fried ecu with doing that.

Just out of interest, can the ecu be damaged but by using the master to turn the car off?