20 Most Recent 1990 GMC Sierra - Page 2 Questions & Answers

did it jump timing ?

short in wiring somewhere

check fuse

Tail & dash lamps operational ?? 1 Add test equipment,test for power/ground signals to park lamp bulb holders 2 Fault trace from there..... If you need further help, reach me via phone at https://www.6ya.com/expert/ralph_2f0886b7d6af32ce

u have a fuel delivery issue may need new fuel pump or fuel filter

you must have a wrong/loose connection to the ignition switch would be my thought

other than changing the identified parts ,which i imagine are expensive ,check all air intake pipe work as a split or worn hose can cause irregular air intake thus giving a false exhaust reading

May want to look at replacing the wiper circuit board.It is located on the firewall adjacent to the wiper motor and has a some what square black cover with 3 torx screws and wireing harness pluged into the side.We had a truck that every time you washed it the wipers would stay on until it dryed out.You can try removing it and spaying it down with contact cleaner just watch the brease on the two contact tips.Well hope this helps.

The heater control,can be anything,but the headlight problem,is most likely the head light switch.

It seems like there is too much fuel compared to the air coming into the throttle body. Did you fit the TBI kit correctly? or is the flap in the throttle body always closed, stopping air getting in.

Here is the firing order diagram for that vehicle and engine.

Usually next to the fire wall in the engine compartment. Follow the two heater hoses.

Is this truck carbuerated or throttle-body injected? If carbuerated, I'd put in a new carb kit...and be sure to replace the accelerator pump. Ethanol in gas today wreaks all sorts of havoc with older vehicles because the rubber and plastic parts manufactured back then were not designed to deal with the problems caused by ethanol. After rebuilding your carb, buy a product called Seafoam and add it to your gas tank at the rate of 1oz per gallon of gas. It will partially offset the problems caused by ethanol.

check earth wires for light circuits and dash