Am having issues maintaining power to my 2006 Ram 2500 Cummins lift pump. We can not find the fuse and/or relay switch to troubleshoot. Where is it located and what would cause the power to stop, then turn back on? We've only bumped to test it.

 

The fuel lift pump will only turn on for 30-60 seconds when you bump the key. The ecm controls the on and off time of the fuel life pump. If im not mistaken its pwm (pulse width modulated) so it never runs wide open all the time the ecm determines the duty cycle of the pump.

 

When you initially turn the key on, the pump will cycle for 1.5 seconds.

If you bump the starter, the pump will cycle for 20 seconds.

How are you measuring or what is causing you to think you have a power loss?

Do you have a fuel pressure gauge that is showing no fuel pressure?

 

We had a fuel error and checked various fuses and connections with a standard test light to make sure everything was getting power...the lift pump was not. However, we did turned the ignition and did the bump and did experience as you suggested. However, we have since removed the fuel tank and are in the process of replacing the pump but are concerned there might be an electrical issue...based on what I see here, perhaps not?