1990 chevy c1500 305tbi 170,000 miles

just picked up a 90 chevy pick up. its the new body style but figured someone with a s10 had a similar problem since its basically all the same, or close to.

anyways the volt gage and lights seem to twitch all over the place randomly. not alot buy noticeable. headlights do too. and the volt gauge goes down about a full volt with each blink of the turnsignal. also have a bad alternator whine through the speakers. i checked the wires under the hood and nothing seems to be grounding out. all the ground straps are connected. i swapped out alternators with my 93 s10 and still the same issue.

other then that the truck is fine. im just kinda paranoid about taking it anywhere far till this is taken care of. any guesses on where to start?

 

Have you gone over all of the underhood grounds to make sure that they are all clean and corrosion free?

 

Visually yes. I really didn't spend any time on it I had to leave. But the wires and connections looked like new. All the ground straps are still there and connected. I will clean them. The gauge reads 9.5 and runs at 12-13v. But the battery is fine and truck has sat a few days and it'll still start

 

I have the same 'pulsating' issue, but without the volt gauge bounce. The voltage is usually around the same 12-13 as yours. I think that the problem started shortly after I replaced the ignition switch but I don't remember if any of that was directly grounded. Hopefully, the answer you get will be the same for me.

 

I did replace the steering column. BUT I only drove it a few miles before I did that so no idea if it was fine before. I rememeber the volts reading low

 

i replaced the ignition switch, did a full tune up, clean all the grounds and positive wires and still the same situation. im getting 14.2 at the alternator and 13.9 at the battery so under the hood its all good. its just the power coming up of the cab is low voltage it seems. checked all the wires underneith. everything seems ok. i can live with it. just that stupid speaker wine is annoying

 

check the main bulkhead connection where the fuse panel comes through.

i ran across something similar a few years ago on a friends truck, and he drove me up the freakin' wall whining about it. i ended up pulling apart the inner/outer halves, and found thaqt a small amount of water was getting in past the old sealer goo (what does GM call it-DumDum?)

anyways, cleaned everything up, resealed it, no more problems.

 

Such a stupid easy thing to try ill do it tomorrow. Ill figure it out eventually or rig it to work just love hearing ideas

 

Hey, I know this is a long shot since this is from a couple years ago, but I have the same problem. Just wondering if/how you fixed it?

 

it was actually a computer issue. i guess what was happening was the computer sets the timing on these trucks and it kept dropping the timing down sporadically for whatever reason. anyways i was lucky enough to have a identical engine including wiring harness and computer sitting in my garage and swapped computers just for the heck of it and that fixed it. been fine ever since

im glad i had that junk laying around i dont think i would have ever bought a new computer