Tech Notes : Lift Pump
The Hummer or H1 Hummer uses an uplift pump to help get fuel to the injection pump from the fuel tank. There is no pump in the fuel tank. This pump can be found in one of two locations depending on the year of your vehicle. Most often the pump is located at the rear of the engine compartment on the drivers side. The pump may also be located along the frame rail near the passenger door. The pump is mounted in a rubber sleeve to dampen the vibration during use. When you turn the key on, the pump is energized and runs for approximately 10 seconds and then turns off. After the engine is started the pump runs all the time. We found several years ago that the pump does not keep up with demand. We saw the pressure gauge actually go to zero. Several years ago at the Hummer Home Coming at AM General, I was talking to a representative and he told me that AMG use to have a pump that would keep up with the pressure and volume needed. He said he didn’t know why they went to a lower volume pump. He also stated that if we had a better gauge we would actually see it go to a negative two pounds of pressure. This tells me that the Injection pump is doing all the work. On our different Stage upgrade kits we include a new uplift pump to help the injection pump out.