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Discussion Starter #1
I'll try to make this as brief as possible:
1995 YJ 2.5 Liter.
Replaced fuel pump and both hoses from frame to tank with new high pressure fuel hose.

Jeep ran ok for a week or two, then left us walking twice. . . .acted like it was losing fuel. Would run both times after a few minutes, but would intermittently fall on its face as if it wasn't getting enough fuel.

Tested fuel pressure: 80-90 pounds and fluctuating like crazy. OK, return line is blocked, right? Dropped tank but left hoses hooked up. Tested again, with tank on the ground Pressures normal, both with and without FPR hooked up.

Now the fun begins: Must be a kink in the line, right?

I cut the hole above the fuel pump in the tub so I could see what was going on.
No kink, no pinch, nothing. . . .but the pressure is crazy if the tank is in place, and ok if the tank is either hanging from the rear, or sitting on the ground.

This makes absolutely no sense, and I'm out of ideas. Have any of you experienced anything like this before? Any help/ideas/advice will be appreciated.
 

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I’d replace all those soft lines in case one just has a week spot and kinks internally. Also pay attention to the rubber block where it goes through the frame. Could be pinching there.
 

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Discussion Starter #3
FIXED!
Lines were new, and I had already eliminated the block (thanks for the ideas, Sequel, I really appreciated the response, especially when they validated some of the stuff I had already tried!)

Somewhere I found a thread (I don't even know what forum it was on) where somebody talked about cutting a little bit off of the return pipe where it joins the bottom of the tank. It occurred to me that that mirrored my problem: Normal pressure when the tank is sitting on the floor, normal pressure when the tank is hanging from the back bumper, pressure crazy high when the tank is bolted into place. AHA! When the tank is bolted into place, the skid plate is pushing on the bottom of the tank, which is sqeezing it up into the pressure return pipe (and the cone shaped gasket that fits over it). I cut 1/4" or so off of the bottom of the pipe, cut about the same amount off of the top of the gasket thingy, and reinstalled everything. Works perfect now.

I've been fighting this for weeks, I can't say how happy I am to have it finally solved. Hope this helps somebody else with crazy high fuel pressure, especially if they've been futzing with the fuel pump assembly.
 
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