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Fuel pressure question for the V8 swappers

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Have a bit of a quandary, so here goes. My YJ sat for about a year after getting it running before making her roadworthy. Stock 4.8, Wix Corvette filter/regulator, Delphi FE0114 pump (Delco EP381 equivalent). Noticed as of late LTFT's have been a tad high (+15 to +23 depending on load), but no P0171/P0174....yet. No vacuum leaks. Have to cycle the key a couple times before starting. 40psi at the rail (should be 58-60 KOEO, 50ish running.....which it was when I first put it together and fired her up a year ago). Drops immediately to 5-10 after turning the pump off. My initial thought is the drainback valve in the pump. My fuel pressure gauge isn't long enough to reach inside the cab yet (need to extend the hose) so all tests done stationary at idle. Blocking off the return line at the regulator still yields 40psi. Deadheading the pump KOEO SHOULD raise it to 75-80, no? Blocking the pressure line after charging the system (and opening the return) will hold that 40psi almost indefinitely.....the SECOND I removed the vice grips, you could HEAR the fuel drain back into the tank, and pressure dropped to 5-10 psi. This SHOULD rule out the regulator, which do fail.....especially the cheap ones (which mine is not). A lot of people have been reporting the hose between the pump and sender have been failing, regardless of platform. I'm pretty sure I have to replace the pump, but I'm a little wishy washy on whether or not it's the regulator....as when they DO fail, you get 40 at the rail as well. Thoughts?
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Everything I'm reading points to your fuel pump being bad. 40 at key on, 40 when blocking the return, and the fuel rushing back into the tank. For the record, when I first did my V8 swap, I was still running the fuel pump from the old 95 2.5L engine and it could handle what my 5.3 could do....although I never took it past 3500-4000rpms. If you're still using a 2.5 fuel pump from 87-90, those pumps can't really deliver the pressure you need.

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Discussion Starter · #3 · (Edited)
I agree with you.....especially with the rash of failures of the small hose that comes with the pump. Seeing more and more of those posts as of late, regardless of type of pump. When I do get a new one, I'm throwing that hose directly in the trash and using a slice of Gates Barricade :D

I used the equivalent to the Delco EP381, mid '90's GM pickup (1st Gen Vortec MPI engines). Same pressure and volume as the later LS equipped trucks. Mine was originally a 4.2, so I had no electric pump at all.....and fitting that sender was a mess all in itself!!!
 

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An experience I had with my 5.3 when I first got it running. I would be driving along 30 - 35 mph and it would just die. I could wait 10 minutes and try to restart and it would fire right up. After a few weeks that turned into every time I pressed the accelerator it would fall on it's face like no gas was being fed. I checked the fuel pressure and it didn't seem right. (been too long, don't remember the numbers). Changed the regulator thinking that was the issue. Nope. Finally decided to take it to the shop to have them analyze it. On the way to the shop I checked it one more time to make sure it was an issue and pressed the throttle and it fell on it's face. Left it there and the next day the shop couldn't duplicate the problem. Brought it home and it has run perfectly for 11000 miles.

My assessment is that there was air in the fuel system somewhere that had to work itself out and it affected the fuel pressure reading at the rail. That was why I was getting the bogus pressure readings. And it eventually worked all that air out and started running perfect.

Your problem. Since your jeep sat for a year. I'm thinking maybe your fuel system has gotten some air in it that won't clear and is causing your issues.

Just my 2 cents. Good luck.
 
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