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ISC Lift Pump Potential Leak BUT It Is Bypassed


Mile Marker 42
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Hello All, I have recently completed an AirDog only pump installation and I have about 45 highway miles of an uneventful test drive under my belt. Everything seemed perfectly fine and I didn't notice any leaks when I got home. On my installation, I capped off the fuel inlet and outlet of the lift pump with 10 AN caps. I left the return lines as is. I mounted my AirDog pump in the bay where my fuel tank is and I am pushing fuel to my factory 2 filter set up. Pretty straightforward. The AirDog pump was preset at 15 psi and that is what the running pressure actually is as I installed a gauge. Today, I started the engine to reach full air pressure as I wanted to chase an air leak. Once it reached full air, I turned off the engine and got underneath with a bottle of soapy water. While under the engine area with a flashlight, I noticed fuel leaking ever so slightly out of the bottom of the lift pump. What? How could that be when I have it capped off? No banjo lines are leaking on the lift pump and neither is the return line from lift pump to tank. Is it possible the manifold is bad and leaking into the diaphragm area of the lift pump? Or, is it just fuel left over in the lift pump possibly leaking out. I am now trying to understand if there is a way to bypass the complete lift pump manifold with the 2 banjo hoses mounted to it? FYI, I only did this mod as preventive maintenance, not because I had a leak or running issues. Any help would be greatly appreciated. Thanks in advance.

Edited by Mile Marker 42
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  • Mile Marker 42 changed the title to ISC Lift Pump Potential Leak BUT It Is Bypassed
10 hours ago, Mile Marker 42 said:

Hello All, I have recently completed an AirDog only pump installation and I have about 45 highway miles of an uneventful test drive under my belt. Everything seemed perfectly fine and I didn't notice any leaks when I got home. On my installation, I capped off the fuel inlet and outlet of the lift pump with 10 AN caps. I left the return lines as is. I mounted my AirDog pump in the bay where my fuel tank is and I am pushing fuel to my factory 2 filter set up. Pretty straightforward. The AirDog pump was preset at 15 psi and that is what the running pressure actually is as I installed a gauge. Today, I started the engine to reach full air pressure as I wanted to chase an air leak. Once it reached full air, I turned off the engine and got underneath with a bottle of soapy water. While under the engine area with a flashlight, I noticed fuel leaking ever so slightly out of the bottom of the lift pump. What? How could that be when I have it capped off? No banjo lines are leaking on the lift pump and neither is the return line from lift pump to tank. Is it possible the manifold is bad and leaking into the diaphragm area of the lift pump? Or, is it just fuel left over in the lift pump possibly leaking out. I am now trying to understand if there is a way to bypass the complete lift pump manifold with the 2 banjo hoses mounted to it? FYI, I only did this mod as preventive maintenance, not because I had a leak or running issues. Any help would be greatly appreciated. Thanks in advance.

Hey for what its worth, mine had a smell like diesel, an after my bypassing the lift pump and capping off both the inlet an output i too had a small seep, causing concern. I washed the out side with parts wash liberaly, let it dry an then drove it several miles, then rechecked it and it was dry. My pump issue was not a leaking gasket as much as mine had been leaking out from the connection where it plugged in at, i suspected the motor cavity had actually been filled with enough diesel fuel that it took it a while to M/T out, i have just compleated a 2300 mile trip an its drier than a popcorn fart. From what i understand the return line fuel does not have any “pump” cavitys, instead it supposed to be just apassage  way thats channeled thru the assembly. To be fair i have never held a lift pump in my hand so that part is just hearsay. Perhaps someone out there who has actually looked at the passegways of the liftpump can comment on that.

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2 hours ago, Rikadoo said:

Hey for what its worth, mine had a smell like diesel, an after my bypassing the lift pump and capping off both the inlet an output i too had a small seep, causing concern. I washed the out side with parts wash liberaly, let it dry an then drove it several miles, then rechecked it and it was dry. My pump issue was not a leaking gasket as much as mine had been leaking out from the connection where it plugged in at, i suspected the motor cavity had actually been filled with enough diesel fuel that it took it a while to M/T out, i have just compleated a 2300 mile trip an its drier than a popcorn fart. From what i understand the return line fuel does not have any “pump” cavitys, instead it supposed to be just apassage  way thats channeled thru the assembly. To be fair i have never held a lift pump in my hand so that part is just hearsay. Perhaps someone out there who has actually looked at the passegways of the liftpump can comment on that.

Thank you, this is what I am hoping it to be. Someone on another forum posted this and I will check in with him. See post 144: https://www.irv2.com/forums/f123/repeating-caps-failures-need-help-289659-11.html

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I had my lift pump replaced recently because of a leak. Turns out the return fuel line going to the fuel tank was leaking at the connector. I have the old pump and you are correct the return line goes directly thru the pump casting. There are four sets of holes in the pump of which two sets are plugged. It must be a multi  use pump. The pump itself only only runs for 45 seconds and    then fuel passes on thru. The return lines are on top and fuel line from primary filter are on the side.

Bob U  2000 Dip

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