Troubleshoot a No Start...then Start

[Finnegan]

Originally Posted by mziggy16

Where is the engine to chassis ground?

I'm going to keep driving it to see if it keeps acting up to, hopefully, isolate more variables (if there are any). At least the ignition switch and clutch stop are ruled out.

I don't know. I poked around working schematics but missed it.

[wdb]

If it's engine-to-chassis ground you can verify with a jumper cable. There's a grounding post under the hood. Connect to that and a bare bolt or similar bare metal object on the motor.

I once worked on a buddy's MGB. It kept melting the plastic innards of the throttle cable. Turned out that the throttle cable was the only thing grounding the engine to the chassis; that poor cable was carrying 20+ amps, more when the starter cranked.

[mziggy16]

Hopefully the final update to the thread:

I replaced the starter over the weekend. It was a bear to remove because the dowel was stuck in place. It took my neighbor and I a good hour to hour and a half to ever-so-slowly wiggle that thing off. Once it came off putting it back together was straightforward and uneventful.

So far, so good on the starts. I'll have to run it through a few of the hot start - sit for 30 mins - then start scenarios, but initial results are good.

Thanks for all of the help on this one!

[Sergio19]

Just in case the issue is not resolved, then it's 99% the ignition switch. For some reason BMW decided to run the solenoid coil current right through the ignition switch (and not a starter relay) so the high current and arcing wears the contacts out over time.

You can take apart the switch and the contact attached to pin 8 will probably be heavily oxidized/worn (lots of DIY on this, common on E46 and similar era BMW). It can be cleaned with a very small file but probably won't last as long as a new switch.

I'm looking into placing diode across the solenoid coil which will suppress the arcing and make the ignition switch contact last much much longer.

[mziggy16]

Originally Posted by srdj

Just in case the issue is not resolved, then it's 99% the ignition switch. For some reason BMW decided to run the solenoid coil current right through the ignition switch (and not a starter relay) so the high current and arcing wears the contacts out over time.

You can take apart the switch and the contact attached to pin 8 will probably be heavily oxidized/worn (lots of DIY on this, common on E46 and similar era BMW). It can be cleaned with a very small file but probably won't last as long as a new switch.

I'm looking into placing diode across the solenoid coil which will suppress the arcing and make the ignition switch contact last much much longer.

The issue was resolved. In my case, it was the starter. I replaced the ignition switch first and still had the starting issue, but it's been good to go since the new starter went in.