Why, would you go so far backwards. That is science experiment on a separate level futility. If you have a problem that concerns your gmt400 series truck , and have road blocks, wouldn't the depth and wealth of knowledge available here be a more productive accomplishment.
I've been fighting the same issue on the truck for about a year now. It's just a toy vehicle not a daily driver. It has a rough idle that I haven't been able to solve. It had a misfire before I rebuild the motor as well. Since the rebuild it basically has all new sensors and normal tune-up items. After it warms up and sitting in traffic it begins to stumble/miss at idle. I've posted several times before trying to solve it without luck. It has a Melling MTC-1 RV cam which should be computer friendly. The duration and lift is only slightly more than the stock cam. The truck pulls hard and doesn't miss a beat while driving. The truck is not throwing any codes Below are the things I checked and or replaced with the use of a lap top scanner.
Compression 146-156 cold
Timing 0 D with brown and black wire unplugged
IAC
ETC
Distributor, coil, wires and spark plugs
TPS (It was actually bad)
ECM (swapped in a junkyard spare)
EGR and solenoid
Purge solenoid
Fuel pressure (13 PSI)
Checked for vacuum leaks (Carb Cleaner and smoke)
Knock Sensor
Probably several things I forgot.
Now other things that I do know that do not seem right which I have a another thread on.
Timing dropped suddenly while I was watching it with a timing light. Reference pulse to the ECM from the ICM seems to drop in out. I connected my scope to the reference wire and confirmed it does drop out. I pulled the distributor and connected my scope to the pick up coil wires and I see a 8 pulses a rotation so that is working. I verified the ignition feed to the coil is constant. I am out of ideas at this point. It is something weird electrical taking place.
You must be registered for see images attach