Fuel Pump Running All The Time

[MJWenrich]

I've posted a question on the 3rd generation forum re: my 2004.5 truck that may cross over the to 4th generation if information I received is correct. I noticed recently that the 04 pump is not shutting off after the usual 4-8 seconds before starting. Thinking it was the pump going bad (I also heard some gurgling sounds from the tank at times) I wanted to know how to best drop the tank. Yesterday, I went to a mechanic who advised that it was likely a relay problem and since the pump runs all the time anyway. And, it is not a problem unless the pump did not shut off with the ignition. He also said later model trucks run all the time, One person on the forum mentioned that as well and that the engine might have received a flash to modify the computer in the 04. I could not find a relay that controls the pump in the power center.

So....with that long winded intro, does it make sense that our fuel pumps on the newer trucks run all the time and if so, when we change fuel filters, why would we need to cycle the switch several times to prime the system? I recently did the filters on the 14 and it took 5 times of cycling until it started, very roughly at first I might add. After the 4th time, it failed to turn over until I moved the key fob to off and removed it. I'm thinking the mechanic might be wrong on this and I may still have an issue I need to address on the 04.

 

[gsbrockman]

So....with that long winded intro, does it make sense that our fuel pumps on the newer trucks run all the time and if so, when we change fuel filters, why would we need to cycle the switch several times to prime the system? I recently did the filters on the 14 and it took 5 times of cycling until it started, very roughly at first I might add. After the 4th time, it failed to turn over until I moved the key fob to off and removed it. I'm thinking the mechanic might be wrong on this and I may still have an issue I need to address on the 04.

Look at the shear volume of fuel removed from the system when changing the fuel filters on a 2013 & newer 2500 HD or 3500 HD.......draining the underhood canister coupled with the fuel lost when replacing the rear frame mounted separator is close to 1.5 to 2.0 pints....based on what I've captured in some jugs over the past 14 or 15 fuel filter changes. After poor success with re-starts after about 4 or 5 primings.....I generally do 8 to 10 primings, and it fires right up.

In addition......I don't think the fuel pump runs continuously until there's a signal from the tach actually stating the engine is running.

 

[MJWenrich]

Good point on the tach being the link. But I wish I knew for sure on both of these trucks. Next time I do the filters, if I can remember that far in the future, I will try the additional priming.