neilcase

1987 5.0 TPI with 5 speed and G92 with 3:45 gears. Total ground up restoration. I let the engine builder talk me into a mild cam grind which the 165 ECM should learn on its own? So it runs great except..... Starts up within a second no matter how long it sits. Runs a little rough in open loop but well under 1000 RPM while in open loop. Then as soon as it hits closed loop it jumps to exactly 1500 RPM and stays there. Hot start up is very slow and required about 5 seconds or more of cranking.

I know zip about tuning and ECM stuff but I was able to figure out how to get an ALDL acquisition reading using TunerPro. TPS voltage reads at 1.49 at rest. But using a voltmeter at the blue and black wires of the TPS it indicates .57. So I swapped out the TPS with two other units and I still get 1.49 EXACTLY at total rest on both of the other TPS sensors. That can't be a coincidence, can it?

Are the high idle RPM and this weird ALDL TPS reading related? And what about the slow hot start?

RBob

iTrader: (1)

Not sure why you haven't received a response yet. So many are ready to jump in.

Anyway, when you state that you are reading the TPS voltage "at rest" with the scan tool. Is the engine running at this point in time?

If so then check the TPS voltage at the ECM. C13 to A12.

If that too is at .57 volts with the engine running and the scan tool is reporting 1.49 volts, the ECM is bad.

If the SES/CEL light works, is it being set?

RBob.

neilcase

Thank you RobR. When I meant "at rest" I meant key on engine off and zero throttle.

And you nailed it. I didn't test the ECM pin outs but rather just swapped ECMs and got good range readings. Then I put my PROM into that swapped ECM and also got good readings and now the car seems to be doing well. It's hard for me to assume that these micro devices go bad because you cant see the "bad" where as it's so easy to see a bad engine or suspension component.

Bad ECM. Case solved a couple hours ago. You called it correctly.