Engine won’t stay running after letting go of key

[Tomo320]

I’ve just carried out some rust repair in the passenger footwell which involved me removing the wiring harness out through the firewall. Before I removed it I made sure to label everything and the car was running fine before hand. Having put it all back together I’m now getting an issue trying to keep it running.

When I put the key in the ignition and rotate it to the first two positions everything works as it should all the electrics come on and I can here the fuel pump prime, everything looks to be okay. When I turn the key to the sprung stage to start it, the engine will fire up and run with no problem however as soon I let go of the key and it springs back the engine will shut off instantly. If I keep hold of the key in the furthest position on the ignition the engine will run fine although the starter motor is still going too. I have checked all the grounds and cleaned the connections, anyone had a similar issue?

The car is a RHD Manual 1986 320i

[BenHar]

Did these have a ballast resister?

Try running a wire directly from the battery to the coil.

Ben

[Tomo320]

Did these have a ballast resister?

Try running a wire directly from the battery to the coil.

Ben

I don’t believe any came with a ballast resister and having a look I can’t see anything on the car like it either,

I’ve tried running a wire direct from the battery to the coil and still getting the same issue…

[rix313]

Did you disconnect the ECU when you did the welding?

[Tomo320]

Did you disconnect the ECU when you did the welding?

I left the main connector in place on the ECU but removed the smaller 3 pin plug that came down from the steering column. The welding was done on the opposite footwell to where the ECU lives and the battery had been disconnected for several days before I did any welding.

[rix313]

I think you should look at trying another ECU. The ECU needs to be fully disconnected for any welding. Welding essentially sends a hoofing big current through the chassis and any delicate electronics stand no chance. It sounds like you were very thorough with labelling everything so if. My first port of call would be plugging a different ECU in to be sure. Not long ago I had a customer car in that ran before welding works then ‘mysteriously’ didn’t after their mate had a go. They didn’t unplug it and it nuked it.

[davidt]

Check the ignition switch as they do faulty.

[Tomo320]

I managed to get hold of another ECU that came from a running car to test and sadly I’ve still got the same issue car will start but die as soon as I let got of the key.

I have tested my ignition switch just using a multimeter and couldn’t see an issue, I haven’t been able to get hold of another switch to properly test it yet, is there a way of by passing it to start the car?

[Blanca]

If you are getting +15 (ignition out) from the ignition switch using a meter I wouldn't look into it any further, the problem would lie in t he connectors in the engine. Shorting +30 (battery, red ) to +15 (ignition) would secure the ignition but if it still doesn't start then as I said look at what you unplugged and reconnected, as that's where you problem lies.

I welded the whole right side of my radiator support / inner wing without disconnecting the ECU and no problems.

[rix313]

I welded the whole right side of my radiator support / inner wing without disconnecting the ECU and no problems.

I cannot stress enough that this is an incredibly bad idea.

[Blanca]

I welded the whole right side of my radiator support / inner wing without disconnecting the ECU and no problems.

I cannot stress enough that this is an incredibly bad idea.

In 50 years, never had a problem.

[rix313]