Engine/Transmission (1998.5 - 2002) Lift Pump cycle

[plongson]

Did a fuel filter change, no big deal but I have a question. . I cycled the key about 20 times and heard the low bump/rumble and then realized that I was not hearing the LP. I bumped the key hard enough to tap the starter then went back to the ON position and the LP ran like crazy an filled the canister. My question...



1. ) What is the "Low Rumble" that is heard when the key goes to ON.

2. ) What tell the LP to cycle and is it tied to the start position on the key.

3. ) Why doesn't the LP run in the key "ON" position until pressure is obtained in the canister.



Just need to know these things...



Oh Ya, Made a cool change to the canister to make the filter change cleaner, as you know, loosining a banjo bolt until fuel squirts out is real messy...

Took a Ray's tapped banjo and used it in the outlet side of the canister, installed a threaded schrader in place of the 1/8" pipe plug. When you need to fill the canister, remove the guts of the schrader and slip a long piece if vacuum hose over and run it into a coffee can. Cycle the LP until fuel comes out the hose. Reinstall the "Guts" and "VIOLA, No fuss No Muss" as they use to say... your canister is primed...

 

[Ncostello]

Anytime you first turn the key to the on position, the lift pump will run for a few seconds irregardless of whether you changed the filter or not. Some go for 2 to 5 seconds. That could be the low rumble you hear. If thats not the low rumble you describe somethings wrong somewhere else. It could sound like a rumble from inside the cab I suppose.



The PCM or ECM tells the LP to run for 30 seconds or so when it senses an attempted start but the engine fails to start. I guess its to try and purge any air out so the next time you try and start it will. Bumping the starter creates a "failed start".



The LP doesn't run for a long time automatically in the on position if there is air in the system because it doesn't know there is no fuel (or pressure) in the canister. Thats why you need to create the failed start mode of operation.



Just as a side note. . if your truck is running and dies for any reason, the LP will stop running. Thats a safety feature I believe. If your in a wreck it will not keep pumping fuel.



I bought a Cummins pigtail adapter and added some extra wire length to it. I just plug that into my pump and hook it to the battery with alligator clips. Then I can let the pump run as long as it takes... also gives me time to check for leaks and crack air bleed valves if I need to.

 

[plongson]

More on the subject..

The low "Rumble", I don't really know how to describe it, only lasts for 1/2 to 1 second. I am familiar with the sound of the LP, I would describe as a whirring sound that lasts, as you say, a few seconds. You get the initial "Rumble" and "Whirr" on the initial "Key on" and then after that, all you get when going from "Off" to "On" is the "Rumble", over and over until you bump the starter and give it the "False Start Signal" that you mentioned. I now understand what the LP looks for to run (from your discription) but the "Rumble" still confuses me. It has done this since day one... Cycle the key, (slowly like 15 sec. between cycles) and see if you can hear a similiar sound...



Paul...

 

[JPittman]

This low "rumble" is it a single "thump" like a bass tone? If that describes it better, it is the ABS turning on. I have that "thump" and the diesel tech told me it was the ABS. Some day I'll remember to have the wife cycle the key with my ear on the unit to see if it really is it.

 

[plongson]

EXACTLY!!

That would describe it to a TEE! I never thought of it that way, but it does sound like a bass thump. Thanks, I couldn't figure what it could be,,,