Starting issues 1983csi

[Gareth91971]

When the car has not been started for a couple of days it turns over but will not fire up. If I come back to it a few hours later or the next day it usually fires up. It seems to start up no problem once it has been running and it runs and drives very well. I have a feeling that it may be an ECU intermittent fault but would appreciate any other owners experiences and expertise as how to diagnose and stop the fault.
Thanks Gareth

[Dschart]

My 1st guess would be fuel pressure. Does your fuel system have the check valve upstream of the fuel rail? Bmw added this because of the issue you have. 2nd guess is weak spark plugs or secondary ignition, i.e. wires, cap, rotor. Corrosion in the cap can cause hard cold starts.

I would put a fuel pressure test gage in line with the fuel feed and watch it during different conditions.

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[jclausen]

Ya I would check fuel pressure and the cold start valve

[DesktopDave]

+2 - I'd be suspicious about the fuel pressure. There might be a check valve in the high pressure pump output. They'll lose pressure after a while, it'll take some time to 'prime' the system back up to full PSI. Also cold start valve, coolant temp sensor can be flaky, but only if cold starts are always the problem.

I've also seen a few times where the main relay was mechanically worn out, or where the crank position sender was a little weak. You can easily swap the senders in the bellhousing, just be sure you keep the plugs matched up on top at the intake manifold brace...otherwise it's a no-start situation. Occasionally the position sender pin on the flywheel is damaged too.

There's a really good troubleshooting guide here too. It's comprehensive, goes through troubleshooting many of the early Motronic problems.