Cummins Lift Pumps - When do Cummins lift pumps fail and what do they affect?
Cummins Lift Pumps
Design and Function
The lift pump is used on many Cummins engines, but most often problems with the pump are associated with the 5.9 ISB. This pump is used to transfer fuel from the fuel tank to the injection pump (known as the VP44 injection pump). The lift pump runs at all times when the key is on.
Signs of Failure
The VP44 injection pump is designed to be fed by the lift pump for proper pressure and lubrication. Unfortunately when the lift pump fails, the injection pump will continue to draw fuel through the lift pump under vacuum. Normally you can tell little or no difference in the engine operation when this happens. However, the VP44 injection pump can not handle this loss of fuel pressure.
The injection pump will eventually be unable to achieve the fuel demand from the engine ECM, causing the engine to derate and feel extremely underpowered. At this time, the injection pump will either need to be rebuilt or replaced (which is very expensive and not at all enjoyable).
The best way to prevent this is to monitor your fuel lift pump pressure. This can be done two different ways:
1.) Install a manual gauge. 2.) Install a sending unit to run an indicator light.
The lift pump should provide 10-15 psi at idle, and no less than 5 psi at wide open throttle (WOT). Cummins supplies a sensor kit that can be purchased, which will turn and indicator light on if the pressure drops below 3 psi. This warns you that you have lost fuel pressure and can have the problem repaired before your ruin your VP44 injection pump.
Fuel lift pumps for the Cummins diesel have been an issue since originally installed with the release of the 24 valve ISB. Cummins has changed designs several times in search of creating a more reliable pump, but it is still safest to know what your pressure is at all times.
When replacing the fuel lift pump, make sure that you check your engine serial # first. Some engines (mostly built before 1998.5) have a wiring harness built into the pump. The new replacement Cummins lift pumps do no have this harness built in. You will need to purchase the harness seperately and install along with the new pump (which is very easy to do).
When purchasing your new fuel lift pump, your best quality and price will be to go through an acutal Cummins dealer instead of aftermarket or through Dodge. Just contact your local Cummins dealer with your engine serial number, or purchase your fuel pump online. There are several Ebay sellers that can check application through your engine serial number and sell you complete kits that come with the new fuel pump and warning light system.