Low Voltage From Rpm Sensor - Car Won't Start

[mulcy]

Hi All,

So I'm finally getting to the bottom of why my 94 850 N/A automatic won't start. After literally a month of swapping parts, I got smart and found a way to patch directly into the connection to the ECU. What I've found is that my RPM sensor is delivering too low of a signal and not allowing the car to start (I'm getting ~100 mV from the sensor. 200 - 300 mV is necessary to get spark.)

I've tried three different sensors, all known good, and I always get the same low voltage. But if the sensor is good, what could be causing the low signal? One of the troubleshooting documents mentioned the possibility of a "deformed carrier plate." I assume by carrier plate they're talking about the flywheel/flexplate? Any ideas for how to fix this problem short of pulling the trans? One thought is that I could try to shave down the mounting on the sensor so that it sits closer to the flexplate. Think this is worth a shot or just asking for trouble?

Thanks All.

[mulcy]

No love? Should I keep trying to fix it? Give up and part it?

[flaco]

A bad ecu maybe? If the ecu checks out, then shaving the mount might help... or you can cut the sensor, might be easier than to permanently shave the trans housing.

[erikv11]

Could it be bad wiring between the sensor and the ECU, rather than at the flywheel? Can you bypass the wiring harness (don't know anything about the wiring path for the RPM sensor sorry)?

[mulcy]

Tried replacing the ECU already with no luck. I don't think the harness is the problem since I get the same low voltage when I plug the multimeter directly into the rpm sensor.