Driving me nuts, 90 350 with TBI

I am getting no reference voltage at the ECM terminal C14, gray wire to MAP and TPS and I have checked all connections to all sensors, grounds and power.

I have tried 3 different ECM's with same result. I feel that something needs to tell the ECM to give 5 volts but cant find the "trigger"

Anyone help me out here please?

Thanks!

 

Where are you testing for the voltage? at the sensor or at the computer itself? there should be a constant 5v reference coming from the computer, even when it's not running. as long as the key is on, there should be 5v. No "trigger" that I'm aware of. maybe the prom is the problem? I don't really know if it has anything to do with sensor function or not, but I can see it being possible. I hope someone jumps in here and corrects me if I'm wrong. I've actually been trying to work out a problem with my MAP sensor only getting ~3.7v no matter what I do. I've replaced the computer, the sensor, repinned wires, the works. If the prom can affect it I'll be kicking myself for not replacing it sooner.

 

Key-on, engine-off (or on), there should be +5 volts at C14. The ECM case is ground so can use that when checking the voltage at the ECM.

Unplug the MAP and TPS and check the volts at pin C14. If not there then the reference voltage wire to the MAP & TPS has to be shorted to ground. If there with the MAP & TPS unplugged then one of them is bad.

Plug one in and see what happens. When the +5 volts goes away that is the bad sensor.

I am assuming that the engine runs, and that the SES/CEL does turn on at key-on, engine-off. If not then check the inline fuse, under the hood, runs along the passenger side fender well.

RBob.