Intermittent starting problem

[1990m3]

'95 s50 motor in '91 318is. I drove the car for nearly 2000 miles after the swap without a hiccup and now all the sudden it is doing this. About 1 in 10 starts it just cranks and won't fire. Motor is getting fuel.

I have some sort of problem with my ignition system I think, since I'm not too familiar with m50/s50 motors I'm not sure what my next step is. My crank sensor is getting proper resistance (approx 530 ohms), and when it fires it runs smooth as silk. Where should I look? What should I test? Start throwing some ideas out there and I'll tell you what I've already done/tested.

If the car won't start I can just let it sit there and within 12 hours it will start, everything else remaining constant. I mean I don't roll the car, shake it, kick it, or anything. It will fire up like there is nothing wrong with it.

Throw some ideas out there, it sucks not being able to drive the car like this...right now it's just totally unreliable and I learned my lesson after it left me stranded for a third time.

Thanks in advance...I'll be checking this thread often

David

[1990m3]

oh yeah, it's almost obviously electrical...any common failure areas in the e36 setup?

[arsevader]

Check your grounds, check your grounds and for the last step....check your grounds.

Especially the one from the block(engine mount bracket on an M50?) to the frame.

[1990m3]

yeah I'm going to go through it again today, but I checked all the ground over the weekend and they were very tight. Guess I'll have to start tracing them back

[Addissimo]

I tell this to everybody who has these problems:

Make sure your ecu is getting power and ground, including switched 12v. Check for power on pin 6 (unless your harness is different) when you're cranking. I completely tore my car apart trying to diagnose a problem similar so what you're having. Not being able to figure it out, i said "fuck it, i'm going standalone." When i was installing my stand alone system i couldnt get power to it. I played with the chasis side of the engine harness, and i wasn't getting power to the dme (for me, pin 6). I started to jigle wires under the dash and I have power now.

-Addis

[1990m3]

I've parked the car for now at my parents house. My dad has a few cars so if it doesn't start he can just take something else. Hopefully I'll get a chance to diagnose it a little more this weekend...the week is quickly getting away from me.

I will snoop around the glovebox and make sure I have power to pin 6, i do suspect there is an issue in the glove box area, maybe even a loose ground. I should look at that tonight actually. I'll get back to you