20 Most Recent 1991 GMC K2500 Questions & Answers

In this link https://www.google.com/search?q=1991+GMC+Vandura+G2500.+Manual ..

put some gas in a spray bottle. spray throttle body and vacuum line if engine raises found leak

May have air lock (bubble) in cooling system. My 91 Sierra did that. Tried everything. Finally installed flush kit between engine and heater core, removed cap poured coolant into flush inlet until fluid ran back to radiator. Heater now will run me out of the truck cab.

It maybe the fuel pressure rugulator inside the EFI Unit. Sorenson makes a rebuild kit with all the gaskets, screens and regulator for about $30. An EFI is the most simplest carb you can rebuild. Check the Hanes manual or U-Tube to see how.

You have set the timing to zero right? Then after you hook the bypass back up what does the timing go to?

The switch is called the PRNDLE and it is located on the lh side of the transmission. There is a known defect with the switches. The connector at the switch melts causing it to become inoperative.

I believe it's located on the transmission itself.

It's screwed in to the transmission case,2 wire plug in,easy to change (this is for a manual trans)

run fault codes to check which sensor is giving the problem. Have a pressure test done on the fuel manifold to check for filter/pump and pressure regulator problems

The reason it worked is because when you banged your tank the bushings in your feul pump started workin. It is actually a old trick when people would break down due to a bad fuel pump. As you can imagine though that will stop to. Just a case of replacing fuel pump.

previously answered

sounds like you may need the encoder motor

ADD Freon. It's a R134 system and the pressure is too low. Trust me add Freon and it will work fine. With a low amount of Freon if you jump the low pressure switch at the accumulator it will be very cold but will not have enough pressure to kick on the low pressure switch.

Check the EGR for proper operation,it could cause this type of issue!

Take it to an exhaust shop to check out the catalytic converter. May not be it, but it could be too.