I own a 1991 I6. It starts right up, but when giving the motor some throttle, it will stumble 75% of the time. If you give it gas very slowly it usually doesnt mess up, but the harder you give it gas-while in neutral-the more likely it is to stumble. I have no idea what it is.

 

Get the codes pulled or pull the codes yourself. To see exactly what part is causing the problem.

Some quick easy things to change would be plugs, wires, cap and a rotar.

Adrianspeeder

 

You have several fuel pumps on this truck. One in each gas tank, and one on the frame. If the tank pump goes bad, this could cause your symptom. The tank pump is only to transfer fuel out of the tank. The frame pump runs the engine. If the supply from the tank isn't up to snuff, the motor will stumble. If you have dual tanks, does it run the same way on both? Hope this helps. Also need to check for any vacuum leaks, and any possible codes.

Robbie

 

When I had my 89 I6 I had much the same issue. I replaced the dist cap, rotor, and wires because when I checked the timing it was 180 out and it was obvious that the position did not change. This cleared it most of the way after the switch it was about 15 out, so a little adjustment later and was running smooth. Changed the fuel filters and it was running like a raped ape. Good luck.

 

Sup AirForce

Adrianspeeder

 

Thanks for the help, but i THINK i may have it figured out, im thinking it may be the map sensor. Just because, i disconnected it and it ran fine, (until i tried to drive it), and when i would plug it back in it would mess up more, i am thinking that the map sensor is going bad, not completely bad, but going bad. But i might be wrong.
Chris