Fuel pump cycling every 75 seconds?
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Reads ***** rules!
Joined: Nov 2007
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From: So.Ca./ N.E. UT
Fuel pump cycling every 75 seconds?
Just noticed this while reprogramming the stereo after the dealer did some warranty work on it. I had the KOEO and kept hearing what seemed like the fuel pump (will get under to verify it is the fuel pump) turning on so I got a stopwatch and timed the interval at 75 seconds. They replaced some broken o-rings in the HPOP and also checked the STC for the extended crank I was having, STC checked ok. It never did this before, any ideas why or what is causing this?
Lead Driver
Joined: Feb 2011
Posts: 8,241
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From: L.A. (Lower Alabama)
If it turns out to be the fuel pump, pressure is bleeding down somehow. I hear 3 sounds in a cold start. First to quit is loudest, injector/glowplug buzz. Then a quieter, dampened buzz that I think is the fuel pump. Then a very soft vibrating sound I think is the CD player. I haven't noticed anything cycling though.
Hotshot
Joined: Dec 2003
Posts: 15,368
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From: Stuttgart, Ar
The fuel pump runs for about 30 seconds at KOEO and then times out. You might be hearing the vacuum pump on the right(passenger) fender well. If it's going every 75 seconds you might have some kind of vacuum leak. Mine only occassionally runs at KOEO and for SURE not every 75 seconds.
Lead Driver
Joined: Sep 2007
Posts: 8,180
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From: Scio, OR
Get down and listen and make sure what you are hearing is actually the fuel pump. From the cab, you might be hearing the vacuum pump, which could cycle if you had a very slow vacuum leak.
I can't say I've ever left my key on long enough to know if the fuel pump cycles, but I don't think it does. I think it should run for a short period after the key is turned on then shut off.
Also, the system does not maintain pressure after the pump shuts off. There is a very tiny air bleed hole at the top of the upper fuel bowl that bleeds off pressure almost instantaneously when the pump shuts off.
I can't say I've ever left my key on long enough to know if the fuel pump cycles, but I don't think it does. I think it should run for a short period after the key is turned on then shut off.
Also, the system does not maintain pressure after the pump shuts off. There is a very tiny air bleed hole at the top of the upper fuel bowl that bleeds off pressure almost instantaneously when the pump shuts off.
Thread Starter
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Reads ***** rules!
Joined: Nov 2007
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From: So.Ca./ N.E. UT
I think you guys are right about the vac. pump. I know where the fuel pump is located and have heard it before, I just wasn't sure because the sound with the windows up seems like it was coming from the right side but farther back than the engine compartment and I haven't crawled under to verify yet, will do and post results. Thanks for the direction!
Thread Starter
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Reads ***** rules!
Joined: Nov 2007
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From: So.Ca./ N.E. UT
Yep, it was the vacuum pump located behind the passenger side battery, guess the sound insulation I put in the cab is working, I could swear it was coming from behind. Now to hunt down the leak, thanks again for the insight.
