no signal from ECM? PROBLEM FOUND!!

[ndevillo]

OK, this is continuing to troubleshoot the suspected fuel problem. There is no spak out of the coil but there is power going to it and the ground wire reading is good. There schematic says that there is a signal called "EST" coming from the ECM on pin 12. When I try to start the car, there is nothing detected on that line which goes to the ignition coil driver which is right next to the coil. There are no codes that show up when I connect A and G on the ALDL. WSould this create a no start condition and is there any other test I can do on the ECM to help see if the problem is the ECM??

Finally found the problem. I was correct thatthere was no EST signal but after reading and thinking about it, the distributor sends the signals that generate the EST signal. I pulled the Opti-Spark and when I removed it, I heard some rattling. Seems the two small screws that hold the rotor on were completely out (hence the rattle). Replaced the screws and started a whole new line of symptom chasing leading to the distributor /Ignition coil control unit next to the coil. replaced it and it fired right up.

Thanks to everyone for the advice and help.

[1990-C4-41001]

EST stands for Electronic Spark Timing -- spark advance in other words. I don't believe this circuit is active until the engine is running at 400 RPM or more. Before your car starts, I believe it is supposed to run on base timing which is determined by the mechanical timing -- cylinder 1 position compared to the timing mark. As soon as it starts and get to 400 RPM, I think it starts using the spark advance information supplied by the EST signal. That's how mine works -- but then, I don't have an Opti-Spark system so hopefully Paul, C4C5, will respond with some suggestions for you beyond what I can offer.

[ndevillo]

Thanks for the insight but Since I don't have service manuals I was following the flow charts in the ALL DATA and was getting my symptoms from there. On the step that told me that is where the problem is, I check the voltage on Coil Driver connector terminal A and D and I found 11.87 VDC, then it told me to check pin B on the ignition coil driver connector, which comes from pin 12 on the ECM, and crank the engine. It told me to look for 1 to 4 volts. There was no voltage there. I could not do the next step which was observing low res signal on Tech 1 (I don't have a tech 1). So I went both ways in the flow chart; one told me to probe the distrbutor electrical connection terminal C with a test light, there was no signal and it told me that it was "faulty ECM conection" or "open ignition feed circuit from the distributor to ECM" or a "faulty ECM". There other path on the flow chart said " faulty EST connection at ECM" or "open EST circuit" or "faulty ECM". to eliminate the open circuit I probed connector to connector for the EST signal and read 0 Ohms.

Any opiions or advice would be greatly appreciated.