Bleeding (Removing Air from the System):
There are two stages to bleeding the fuel system on the Diesel Hummers.
- With pump running, open the bleed valve on top of the fuel filter until only clear fuel (no air bubbles) comes out. Then close the valve while the pump is still running. 1/2 to 1 turn is enough to open the valve, then wait for clear fuel to exit. (This makes a mess.)
- On TD Hummers, the pump will run for the first 30 seconds or so after the key is turned to the "On" position (not "Start"). If 30 seconds is not enough, turn the key off, then back on again. It is much easier with a helper.
- On all Hummers, you can jumper the fuel pump wires to hot and ground. There is a connector a few inches from the pump. Black is ground, gray (or white, sometimes) is hot.
- If the above does not fix the problem, you can also crack open one of the injector line fittings to bleed the injector pump. You do not always need to do this part, particularly if the engine will start. If it will not start, you should crank the engine during this process. It is not usually necessary to bleed more than one injector.
Opening the water drain on the fuel filter bowl while the truck is running may introduce air into the system, and is not recommended. It will not let any air out anyway, since it drains from the bottom of the bowl.