M20b27 Not firing when warm

[FLapkacle30]

Hello folks, I've been scratching my head over this for a while now

Car won't fire after its warm up idle stops. Runs and drives just fine, but once its shut down after the warm idle it won't fire again.
Turns over, but no spark.
Engine is standard except I replaced the twin pump setup with a deatschwerk 300, also replaced the fpr with another standard one. ( about a year or two ago )

Just replaced the ignition coil as well.

Thoughts ?
Thanks all !

[varg]

So you've pulled a plug wire and verified that it's a no spark condition? Is the coil getting power?

[FLapkacle30]

no power at coil, ( new coil as well ) fuel pump not grounding when ignition in firing position

Ordered a new cps, hopefully that fixes it

[ForcedFirebird]

Always first thing on an eta no-fire is to check the resistance on the CPS's.

They change resistance once warmed up, so that can complicate things, but they are really simple computers. Seeing the fuel pump wasn't engaging, I would gather the engine speed sensor was the bad one (the one on the starter/flywheel) ring gear. This is the one that tells the ECU the engine speed and the ECU will only energize the fuel pump relay when it sees engine speed. The other sensor (cylinder identification) tell the ECU when #1 piston is on the compression up stroke. If either sensor is bad the engine will not start, but if one is bad you can push start if it's a manual (IIRC its the cylinder identification that can be bad, been a long time since I owned an eta). The sensors are interchangeable and have the same plug, so be weary of which one goes to which wire on the harness.

[FLapkacle30]

Forgive my ignorance, is speed sensor the same as cps/reference sensor ?

Because my odo/speedom hasn't worked in years, just haven't bothered to replace it.

[ForcedFirebird]

Forgive my ignorance, is speed sensor the same as cps/reference sensor ?

Because my odo/speedom hasn't worked in years, just haven't bothered to replace it.

Vehicle speed is the sensor in the diff. Speed sensor on the ring gear is the engine speed (one of the "crank sensors").

[FLapkacle30]

well ill try the engine speed sensor first, if that doesn't fix it ill change out the cylinder position sensor / dme if it goes that far.

out of curiosity, why aren't engine speed/ cylinder position sensors one in the same ?

Sounds like both sensors do the job of a normal crank position sensor, but none here are directly pulling data from the crank- just teeth from the fly wheel ?

Thanks for your help and info !

[ForcedFirebird]

well ill try the engine speed sensor first, if that doesn't fix it ill change out the cylinder position sensor / dme if it goes that far.

out of curiosity, why aren't engine speed/ cylinder position sensors one in the same ?

Sounds like both sensors do the job of a normal crank position sensor, but none here are directly pulling data from the crank- just teeth from the fly wheel ?

Thanks for your help and info !

Electronics in the 70's (when the m20 was designed), was not what it was just a few years later. The sensor on the ring gear determines the engine speed, the other one tells the DME when a particular cylinder is TDC. You are correct, more modern (even as early as the m20b25) they combined the two sensors with a missing tooth on the trigger wheel.

Check the resistance on them before purchase. If the car won't start and the resistance is out of spec, there's your answer.