sactocharlie

I read these post alot and I see alot of problems but hardly ever a final solution. So, with that said I'm going to describe the problem with my truck and what I did to find the problem. I have always found the problem but only after spending alot of cash buying parts that I didn't need. So when she started missing after warmup, I knew that this would be expensive. Since the vehicle still started and made it to where I needed to go I limited my time working on it till after work. I started by getting hold of a scanner, Mod MT2500 snap on. It's an old scanner but my trucks relatively old. Scanners tell you alot but not this time. It told me everything was fine. No codes, no specs out of the ordinary. After the engine warmed to normal operating temp, about 200F on the CTS, is when the problem starts. There was one reading that looked a little off and that was timing. Accelerating when cold it advanced slightly then retarded slightly. No problem with that. After warm up, it no longer advanced but retarded 10 to 15 deg more than when cold. At the time I attributed that to going into close loop. In retrospect I wish I would have given it more attention. Did I mention that the first day I started working on it, the poor performance had already been present for a week. Anyhow, the third evening it wouldn't start. Either I created a new problem or the existing problem finally failed altogether. Fortunately for me it was Friday, giving the weekend to nail it down. First I determined I had no spark. Then I found no fuel. Fuel pressure was perfect. Oh, most might know this but those who don't here is something to be aware of. The 10 seconds you here the fuel pump running after turning the key on is just a tease. The real fuel pressure to the throttle body does not exist until the motor is turning and running. You can go around that if apply 12 volts from the battery to the fuel pump circuit but the ECM only runs the pump at low speed for the ten second prime. No fuel, no spark, fuel pressure good, coil good, injectors worked with scratch test so ECM is good. Got a light at tach terminal and flashes when cranked. Some say that is a good indicator that coil is weak. But resistance test indicated otherwise. I checked the resistance on the pickup coil and it was 900 ohms. I did notice that insulation was heat damaged. I pulled the dist and replaced the pick up coil. Either of the conductors could have been grounding out since bare wire was visible. Put it back togethe, no start. But I need had fuel but not enough spark. I pulled the ignition module and had it tested. It failed for strength, that's what the LED was labled. I wish I had a schematic for an ignition module. Chevy is doing a good job keeping it a black box device. After that she started today, Tuesday 8/24/2011. Conclusion the bare wires connecting the pickup coil expanded and grounded out intermittently when hot. Finally causing enough stress on the module to cause it to fail. Hope this helps somebody, this is by far a PR for longest post.

94 Silverado 1/2 ton with 5.7L 4l60E.