have a '96 changed everything from TPS, distributor, rotor, cap, fuel filter, fuel pump, ignition switch, both O2 sensors and ignition coil. At cold startup starts runs for 15-20 seconds cuts off. restarts and will repeat same problem. I have had it to an electrical specialist but it wouldn't fail for them so no love. it will run sometimes for a week without any problems but now it is failing again with no codes or lights. when it cutsoff sometimes it will just turn without starting up wait a few minutes it will start but will cut off again, it has 185,000 but the engine is still smooth. when you do get it going it will cutoff going down the road like you shut the key off. it is my son's truck and i know i'm missing something that will fix the problem. A mechanic has told me to replace the ECM but i am not sure that is the fix.

 

Welcome to CF.
It could be the Crankshaft Position Sensor. This will tell you how to check/replace it.

 

Or the pickup coil (AKA the cam sensor) causing what you had described.

 

It's not uncommon for the plugs on the PCM to develop issues. A quick and easy check is to wiggle the connectors while the engine is running to see if you can cause it to stumble or stall. You might also try pushing on the face of the PCM without disturbing the harness to look for the same stumble stall condition which would indicate and faulty connection inside the PCM.
IF it's the connectors you can do a couple of things. Replace the ends which is a bit of a pain or you could unplug the connectors and spray them out with some contact cleaner, allow 10 mins for them to dry, smear a little dielectric grease on them and reinstall them using wire ties to better secure the plugs to the PCM by wrapping the wire tie completely around the PCM over top of the connector using 2 wires ties on each plug.
I had similar issues with my 97 GC and I used the wire tie approach, it's been about a year now with not even so much as a hiccup.

 

Thanks to all that have responded back. i am troubleshooting it know.

 

sorry , i can not figure out how to start a new thread/post a question. ok- got a '92 larado that won't start. i have replaced everything! from crank shaft sensor to the brain(ecm)!! before replacing the brain it wasn't getting any fire to it. now have replace the brain and it's firing....but still won't start. it just keeps cranking. so, please help! lol..

 

Where is the cam sensor/ pick up coil.

 

Check the neutral safety switch.

 

In the distributor, under the rotor.