ThirtyFive 21

Currently I have a M1151A1 that shuts off at Wide open Throttle. At times it shuts off after start-up. My mech. has replaced the mechanical lift pump, inspected the air filter, air horn, bleed the fuel system. He's to the point where he has loosened all the full injection nozzles to see if they leak (they don't). That's telling him that (1) the lines may be clogged or (2) the fuel injection pump may be bad. Is there a way to inspect either or? Or maybe you can chime in on the fact that we are way off and it could possibly be something else.

Is there fuel in the fuel filter? If not, then he needs to bleed the fuel lines up to that point or check and make sure the mechanical fuel pump is pumping fuel from the tank. I have had mechs install the push rod and have it "fall" when installing the mechanical pump and it will still turn over and not actually pump. I had an M1167A1 here that took me awhile to bleed the fuel system correctly. Also, make sure there is fuel in the tank, just because the gauge reads "Full" doesn't mean it really is and the fuel gauges are known to read full when they break.

Not sure if you figured it out by now since this a little old but...

If all the steps mentioned above have been checked and are good and the truck runs fine otherwise, you can adjust the fuel injection pump flow. The steps are in the IETM but in a nut shell, pull wires 54A/B, remove 3 screws (security torx bits, tool is in GMTK) from upper assembly. Inside you will see 1/2" nut next to a spring. Turn that nut 1/2 turn at a time (when looking from the front of the truck, start with your wrench on the right and move the wrench left) and re-install all components. Test to see if it solves your issue, if its better but not enough do it again until it's good.