20 Most Recent 1990 GMC K3500 Questions & Answers

You are jumping to conclusions. Slow down.
No spark AND no injector pulse indicates none of the desired outputs were triggered. The ignition module makes spark when it receives a crankshaft position sensor signal, and then transfers control of that spark to the computer after it starts. The module takes its crank sensor signal and generates an RPM count that it forwards to the PCM(main computer) which is used for triggering the injectors and controlling timing. SO, if you had a bad crank sensor OR a bad ignition module, you could lose both spark AND fuel. a coil would not disable injector pulse. modules RARELY fail in a manner that disables RPM reference to the computer causing it to not fire the injectors...At this point, I would TEST the crank sensor as the next step. If its easier, 1 of the wires on the module goes directly there so you can test the crank sensor at the module.

Sounds to me like a bad ignition control module.. very common in gm vehicles.

You can find free wiring diagrams here http://www.bbbind.com/free_tsb.html Enter vehicle info. Year , make , model an engine size . Under system click on brakes .under subsystem brake control will show on it's own . Click the search button .

You need to run a fault code test, to see if you have ignition problems and also do a fuel pump pressure check. To do a fault code test follow the link for instructions. FAQ How to read older GM codes for free

18436572

check the fuse in the computer management any sudden fault it will blow the fuse. on this model they were fitted. you will need to open the computer and using a meter check the fuses on the board. hopefully the chip has not been damaged but as you say by passing it runs the engine. so this is what i would say it is doing or not doing in your case ( not starting) board has a few fuse in side soldiered to the board

take line off before filter see if gas is coming out at time of key engagement, if not its fuel pump.if yes then reconect and disconnect on outlet side of fuel filter this will tell you if filter is clogged

How long has it been since the previous start? If the truck started fine the time before failing to start, you probably have a fuel pump failure, or possible ECU unit failure. Are there any Fault lights showing?

you have direct power going to the starter. You have to find the short. Pull ignition fuse and look for burns inside the fuse box. Follow all wires coming off the new starter. Look at all associated ground wires. If that cannot be found, it may be a short in the ignition itself,