Car shuts off randomly, won't start until engine is cold

[D_bender]

My 1985 325e started having this problem. The car will shut off randomly usually when it gets warm. The car won't even try to start until te engine gets cold again, atleast an hout later.

[D_bender]

Anyone?

[D_bender]

So far changed cranks sensor, and Cap and rotor

[LounsRacingInc]

Check BOTH the speed reference and the crank position sensor, they are located on the bell housing by the slave cylinder, unplug them and test the resistance, they should be at 960 ohms +/- %10 (unfortunately I cant remember the wire colors to test). Using the same pins, also test for AC VOLTAGE....AC, not DC, have a buddy crank the motor over, you should see greater than 250mv AC. do both tests when the motor is cold, then start it and warm it up until it dies, then do the tests again. I'm willing to bet your sensors work fine when the motor is cold and then start to lose their response when warm

[LounsRacingInc]

If the sensors both turn out good, get a 12v test light, (if you don't have one autozone/advance/napa/etc. sell them for like $5) hook it to a ground and then hold it on the negative terminal on the coil. Have a buddy crank the engine, you should see it flicker. If it does, then you know the issue is with a sensor other than the CPS, if it doesn't then the ecu is not grounding the coil like its supposed to.

Edit: I would actually do this test first

[dnguyen1963]

Are you sure your car has no vacuum leaks?

[D_bender]

Ok. Both sensors are good, Ignit ion coil does light up. I just put in a new coil, Cap and rotor, and crank sensor

[D_bender]

I tested for spark and I am not getting spark

[D_bender]

What Else Could It be?

[dnguyen1963]

Borrow a working DME from someone. I suspect that the ignition coil is the culprit, but you said you tested it already.

[D_bender]

I changed the ignition coil with a new one, also I've tried to use a different dme and still won't start when warm

[D_bender]

What else could cause this?m?

[D_bender]

????

[dnguyen1963]

I changed the ignition coil with a new one, also I've tried to use a different dme and still won't start when warm

Does it start cold? If it does then I suspect vacuum leaks are causing the warm no-start.

[Kershaw]

Things expand when warm, usually vacuum leaks are present when cold, but not warm. That doesn't make sense to me. Also, the fact that it doesn't even try to start at all, like no cranking, means that it's probably not a vacuum problem. Sounds more like a grounding issue. The hot/cold thing doesn't make sense though.

The only thing I can think of is heat soak. A hot wire will have a greater resistance than a cold wire. So it may be that something is getting funky when the hot engine heat soaks the engine bay.