I recently bought a 1991 5.2 4x4 and shortly thereafter began to run down some problems...check engine light, low oil pressure light, volt meter malfunction, etc., etc.
I found this forum and got lots of good info and tips on troubleshooting.
My first problem that developed was a no start which I traced down to the ignition switch and got that replaced...the next week charging system failure, I replaced the battery, which was new but too small for the truck, then the alternator after Autozone check said the "internal regulator" was bad..I got a new alternator which was not entirely wasted money, but still no charge to the battery...I began to trace thru the wiring and found an aftermarket voltage regulator spliced into the system and hidden back on the firewall...after a couple of hours here I decided that the ECM was the problem, since the VR is done by the computer...so, new computer and today I fired her up after new plugs, wires, cap and rotor...she started right up but the voltage meter was still showing a slow discharge as I drove around, and the check engine light was still on...but then after about 4 miles, the light went out, and the voltage meter shot up to charging range...I had read here that after a new ECM the computer had a re-learning period...apparently that is true...So now the truck runs great, sounds great and is staying charged!
So thanks to all of you who take the time to share your knowledge. As for the truck, I have also replaced the serpentine belt, power steering pump, rear shocks and tires (235-75-15 since the truck had some fairly nice aftermarket wheels). Next I plan to do the front shocks and clean up under the hood and maybe lose the factory air intake and cleaner...then hit the beach and see how the 4x4 works!
See you all around!

 

Cool! I'm glad we all could help.