jv9999

I'm working on resurrecting an '87 and I have a TPI question. I disconnected the EST cable and set the advance to 6 deg, but when I plug it back in, it's still 6 deg. Also my scan tool says it's 25 deg even though it's still at 6 (idle). I assume this isn't normal? It will advance as I raise the RPM.

It's recently rebuilt with new Bosch III injectors, but it idles like crap with low vacuum. Can't find any leaks with propane.

Cliff Harris

The ignition module controls the spark until the ECM determines that the engine is running. Then the ECM puts the ignition module in bypass mode and takes over control of the advance.

Have your ignition module checked. Also look at the EST connector and the 4 wire harness coming out of the back of the distributor.

My ECM sets the advance to 20° at idle. Yours might be calibrated differently, so 25° seems reasonable.

MikeT 90 C4sixer

Did you reset your ECM, after you disconnected the EST bypass? When you do this, a code should be set in your ECM, and check engine lite on. Need to clear that bypass mode, so the ECM goes back to normal ignition timing.

jv9999

No, I wasn't aware of that. Thanks!

Cliff Harris

Since I just timed my engine tonight, I have some insight here. I started the engine with the EST connector connected. Since the distributor had been out, I had positioned it in what I think is the optimum position (parallel to the firewall). The engine started instantly and I unplugged the EST connector. The idle immediately dropped in RPM. I checked the timing and it was about 5°, so I adjusted it to 6°. I plugged the EST connector back in and the idle did not change, so apparently the ECM remembers that it is not controlling the spark. I shut off the engine and restarted it and it idled normally.

You'll get an error code 42 by disconnecting the EST connector. You can clear it or it will go away by itself after 50 restarts without errors...

MikeT 90 C4sixer

Interesting insight. I was going to guess the code as 42, without looking it up! 50 re-starts is alot, for a car that does not get driven much.