ISC Lift Pump Potential Leak BUT It Is Bypassed

[Ljwt330]

Originally Posted by Mile Marker 42

No, luckily I don't have any oil leaking. It was diesel fuel. I am hoping someone has a exploded view of a lift pump to confirm the return side doesn't intersect the fuel side. You think I should remove the 3 bolts that hold the pump part of the lift pump to the body and remove the pump and fire up my engine to see if any fuel leaks out? That would solve my mystery.

I guess my first question would be, is the fuel dripping from the bottom of the lift pump motor, or down the sides of the motor housing? If it's coming out of the motor itself, the shaft seal failed and fuel is seeping through the insides of the motor and out the bottom.

If you can access the entire assembly from the top, you should be able to see if there is any seepage around the caps or from the gasket area.

Removing the three bolts and lift pump motor should show whether or not there is fuel remaining inside. That alone may answer your question. If you find any, dump it out, dry the interior area, bolt the motor back into place, and fire up the engine. After a few minutes, remove the motor and check the area again. Fuel present? Then it's coming from the return passage. Still dry? It's coming from somewhere else or the problem has been solved.

I suggested the more complex steps above because I'd be a little leery of starting the engine with the motor removed in the off-chance that there is some connection between the passages and fuel would spew out over the engine.

[TR4]

Originally Posted by Mile Marker 42

No, luckily I don't have any oil leaking. It was diesel fuel. I am hoping someone has a exploded view of a lift pump to confirm the return side doesn't intersect the fuel side. You think I should remove the 3 bolts that hold the pump part of the lift pump to the body and remove the pump and fire up my engine to see if any fuel leaks out? That would solve my mystery.

I had the exact same question. Before I started my Fass conversion about four years ago I wanted to confirm this. From all I read, the return section of the manifold is separate. This makes sense since fuel pressure on the pump side would just bypass back to the tank. And, when the pump is no longer running, you would pull in air from the return section.

See post 144 here;
https://www.irv2.com/forums/f123/rep...289659-11.html
dons2346 took his apart, you might PM him to confirm.

Bill

[Mile Marker 42]

Originally Posted by Ljwt330

I guess my first question would be, is the fuel dripping from the bottom of the lift pump motor, or down the sides of the motor housing? If it's coming out of the motor itself, the shaft seal failed and fuel is seeping through the insides of the motor and out the bottom.

It is slightly dripping from directly under the motor of the lift pump. I can get to the top to see, thru my bedroom and nothing else is showing signs of fuel. Only thing I can think is I disturbed the gasket while wrenching on and off the hoses and caps for the install and fuel remaining in the pump is simply coming out. Thx.

[Mile Marker 42]

Originally Posted by TR4

I had the exact same question. Before I started my Fass conversion about four years ago I wanted to confirm this. From all I read, the return section of the manifold is separate. This makes sense since fuel pressure on the pump side would just bypass back to the tank. And, when the pump is no longer running, you would pull in air from the return section.

See post 144 here;
https://www.irv2.com/forums/f123/rep...289659-11.html
dons2346 took his apart, you might PM him to confirm.

Bill

Good find and thank you Bill. I will study that thread and possibly reach out to him. I tightened the lift pump 3 bolts yesterday in the off chance remaining fuel is seeping out the disturbed gasket.

[Mile Marker 42]

Originally Posted by TR4

I had the exact same question. Before I started my Fass conversion about four years ago I wanted to confirm this. From all I read, the return section of the manifold is separate. This makes sense since fuel pressure on the pump side would just bypass back to the tank. And, when the pump is no longer running, you would pull in air from the return section.

See post 144 here;
https://www.irv2.com/forums/f123/rep...289659-11.html
dons2346 took his apart, you might PM him to confirm.

Bill

He wasn't able to offer anything. Thanks any way.