Intermittent Starting Issue. Need Opinions/Diag

[richardM30]

Okay M20 pros (and trolls), see if you can tell me what's going on here.

89 325i 'vert.

Runs and drives fine, no major issues really.

Except once and a while the car won't start. It'll crank and crank and crank and crank until the cows come home, but nothing.

Then I'll disconnect the battery, let it sit 5 minutes or so to ensure any residual charge has drained from whatever, and 9 out of 10 times it fires up instantly.

I've replaced the crank position sensor (that was my guess), but it still persists.

Someone told me that they think it's the OBC malfunctioning - it's perhaps triggering CODE and preventing it from starting?

I can't think of anything else that would really cause this kind of issue - when it starts, it's perfect. No issues whatsoever.

Anything else I could try? I have a spare OBC I can swap out.

Thanks!

[dnguyen1963]

Check those elbows going into the throttle body. When they are loose, they introduce too much air into the system causing a non-start.

[jlevie]

Have a smoke test run and fix any leaks. Replace the O2 sensor if it has 100k on it, the main and fuel pump relays with OE/OEM parts, the distributor & ignition wires with OE/OEM parts, and the plugs with NGK ZGR5A's. There are other possibilities, but start there.

[mpowerful]

One of your relays could be stsrting too poo out.