The Importance of Fuel Lift-Pump Supply Pressure

The light-duty diesel trucks by GM all feature a lift pump designed to deliver fuel from the fuel tank to the injection system. Their importance to the overall operation of the engine cannot be overstated. Without proper lift pump pressure and delivery flow, the injection system in these trucks will not be able to function properly.

Testing lift pump pressure is a relatively easy task and one, which should be done periodically to assure that the lift pump is healthy.

Heath Diesel produces fuel pressure test gauge kits for the 6.5 diesel and these are listed below.

GM 6.5 Diesel
The GM 6.5 turbo-diesel engine found in the ’92-’00 truck, Suburban and step van is supplied by a frame-rail mounted electric lift pump. This pump is powered by a relay when the engine’s starter in engaged and by an oil pressure switch while the engine is running. It is designed to supply the fuel injection pump at a pressure of approximately 7 psi at idle. The more important fuel supply pressure reading, though, is that measured while the vehicle is being driven.

The Heath Diesel Power fuel pressure test gauge kit for these 6.5 vehicles is connected to the fuel filter drain cock which is located near the thermostat housing at the front of the engine. The drain cock features an outlet nipple onto which a drain tube is installed. The HDP Fuel Pressure Test Gauge (Part #HDP1456), features a specially sized hose, which is slipped onto the nipple of the drain cock after the drain hose is removed.

The HDP test gauge is taped onto the exterior surface of the windshield for viewing while the vehicle. While driving, fuel pressure should not go below 2 psi and should, more ideally, be in the range of 2.5-3 psi.

Heath Diesel Power supplies a Heavy-Duty Version of the Factory Electric Lift Pump (Part #HDP1300). Heath Diesel Power also supplies the relay and oil pressure switches used in these vehicles here.

Feel free to contact Heath Diesel Power with any questions you may have regarding issues you are experiencing with your vehicle. We are always happy to help.

- Bill Heath

Related Links:
Lift Pumps
Testing Tools
GM 6.5 Diesel Parts