Random no-start... ignition switch?

[603Racing]

I thought I had seen it all... but NO! Please read details below and let me know what you think. Did I overlook something?

'84 325e

I have an issue where randomly my car won't start. This happens about 4 to 5 times a month... this is my daily driver. I've been mechanically restoring this car for months, this issues still persists and it's very random. Warm start, cold start, sitting for a couple days, sitting for 10 minutes, full tank, nearly empty... happens whenever.

When the issue happens the car cranks normally, fuel pumps spin up, but it does not start. I don't know if it's spark, injector firing, or both. The reason I don't know is because it's random and if I repeatedly turn the car off then try again it usually starts after a dozen or so tries. When the car starts it runs great and gets great mileage.

This is why I think it is the ignition switch. That and almost everything else has been replaced within the last 6 months:
fuel pumps
plugs
crank sensors
fpr
icv
main and fuel relays
fuel filter
AFM
ECU

[jlevie]

The fuel pump is controlled by the DME and only runs when the DME is running and seeing timing data from a rotating engine. If you know for certain that the pump is running when cranking, the no start can't be the ignition switch as it is what causes the DME to run.

[603Racing]

I have a loud fuel pump and I can definitely hear it running when cranking. I did swap both pumps a 2nd time just to be sure. The work around is to repeatedly try to start the car in short intervals. Like I said, usually about 8 to 10 tries then it fires immediately and runs fine. It has never had an issue when running and has never died while running.

I have also already jumpered the two green wires to the OBC relay box, I ran into that issue a while back.

[603Racing]

I was finally able to do at least a bit of trouble shooting when it no-started again. I'm getting fuel (volume at least). Not sure of the pressure, but I think I'm not getting spark. I have a spare coil I'm going to swap in.

Any ideas on what would cause a random no spark issue ONLY at startup? It has never had an issue while running, only random no-start.

[jlevie]

A random no spark, but the fuel pump running, would be a problem with the coil, wiring between the coil and the DME, or a fault in the DME.

[603Racing]

I've swapped DME's, again just to be sure.

I may have been incorrect on the motor getting fuel. The fuel pumps run, but when I put a noid light on the injector harness to test for signal, the damn car started right up so I don't know if the injectors were getting signal or not when the car wouldn't start. I'll have to wait for this random no-start to happen again before I can test it. This last time it happened, trying it over and over again didn't resolve it. Then 2 days later when I went to test it is when it fired right up... so annoying.

I went ahead and replaced the ignition switch with a spare I had. The old switch visibly looked ok.

[603Racing]

So it's not the ignition switch. Swapped it and had a no start issue the next day. Started on the 4th try this time. I am going to try the coil next. If that doesn't fix it, I'll try a 3rd FPR. Just glad I have all these parts sitting in my garage.

[603Racing]

Swapped the coil, still happens. I was messing with the two CPS wires while it was no-starting, then it fired right up. Not sure if it was coincidence or not. No matter, the new owner can fix it. :)

[NoM54me]

Doesn't sound like a coincidence, you may have found your problem. Have you checked resistance on the sensor?

[603Racing]

I did previously and they were within spec. They are only about two years old. Could be a short on the harness side of the connection. I sold the car, so no more worries for me.