Top 20 1988 GMC S-15 Questions & Answers


sounding like a cracked or broken vacuum line, could also be the adjuster screw has a build up on it as well, on the stopper. but sounds like a vacuum leak.could be on the lines or on a diaphragm moving part. you would need to use a leak tester.

1988 GMC S-15 | 35 views | 0 helpful votes


hey there my best bet solution would be to remove the c clip and wrap some wire round it a few times to solve the problem..

1988 GMC S-15 | 24 views | 0 helpful votes


Clearly some fancy diagnosis and testing is needed and checking the fuel pressure will be part of those checks as would testing the injector spray patterns.
If the injectors are producing droplets that are large or are dribbling or leaking the oxygen sensor will see the result as a lean mixture and increase the injector duty cycle making the situation intolerable at idle when the intake air speed is too low to break up large fuel droplets.

Just an idea...

1988 GMC S-15 | 69 views | 0 helpful votes


Hi Chris:
Odds are that the appropriate Haynes Manual would not only have the diagram, but also all of the step by step instructions.

1988 GMC S-15 | 145 views | 0 helpful votes


Blue smoke is almost always oil in the cylinders. It's caused by bad valve seats or bad rings. Timing won't cause blue smoke.

1988 GMC S-15 | 91 views | 0 helpful votes


COULD BE A VACUUM LEAK. CK THROTTLE CABLE, FREELY MOVING TOO. SOUNDS LIKE VAC

1988 GMC S-15 | 73 views | 0 helpful votes


Trace the wiring harness at the rear to see if its rubbed through anywhere. Check all plugs are fully home and plugs pins are in good condition, not corroded or wet. Next check the ground leads on both rear lights to see if its an earth fault sending current to both bulbs. Next, remove one bulb and see if the other functions normally. Then try other way round. See if that shows up any fault.
Also, if you have a trailer socket, check that for cross connection etc.

1988 GMC S-15 | 36 views | 0 helpful votes


Short in wire.. look under the rear of the truck.. find the tail light harness.. take your volt meter and see if it is flashing there.. if not than the short is in the harness running up to the rear lights.. If it is flashing there trace forward.. could be anywhere between that connection and the flasher.. Post a comment and let us know what you find..

1988 GMC S-15 | 30 views | 0 helpful votes


Change the temperature control sensor to the front if the engine near radiator
1 start the truck let it run till you think it is at normal operating temperature
2 unplug the temp sensor if the idle changes then the sensor is bad

1988 GMC S-15 | 292 views | 0 helpful votes


what year, what engines, the blue box , above contradicts.

1988 GMC S-15 | 324 views | 0 helpful votes


Did you check the fuel pressure before you replaced the pump ?
Can you spray carb cleaner or starting fluid into the throttle body and make the engine want to start ?
If it is throttle body injected, can you see the fuel spray when you crank it hot ?

1988 GMC S-15 | 204 views | 0 helpful votes


the injector has high current to it. It locked up and over heated. U should tear the heads off and check for damage in cylinders.

1988 GMC S-15 | 55 views | 1 helpful votes


I suspect that you have some sort of immobiliser connected to the seat belt system and that area has moved and not allowing the circuit to be made for starting. A sort of can't start the car unless the seat belt has been applied. Try clipping up the drivers seat belt for starters or check if there is such a requirement in the car.

1988 GMC S-15 | 35 views | 0 helpful votes


keep bleeding the system,if u didnt bench bleed the master cylinder,you will need to do that.Its a must

1988 GMC S-15 | 464 views | 0 helpful votes


well hopefully the engine is not siesed get a socket and a cheater and find the main pulley witch turns the crankshaft and see if you can crankit if you cant then chances are it locked up

1988 GMC S-15 | 53 views | 0 helpful votes


There should be two ECM fuses. Number one powers the injectors and some of the solenoids along with the ECM. Number two or B powers the fuel pump relay and the rest of the ECM including the sensors that provide data to the ECM. Both are 10amp circuits.
You may need to get a shop manual to have the wiring diagrams to troubleshoot the circuits.

1988 GMC S-15 | 390 views | 0 helpful votes


First off I'd thoughly clean underneath with maybe brake of grease cleaner. after dried, place a long piece of cardboard underneath to positively determine where the leak is. leaks do travel and can mislead you to the location of the problem

1988 GMC S-15 | 150 views | 0 helpful votes

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