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Vortec 5.7 Fuel Pressure

11K views 8 replies 4 participants last post by  Gas-man 
#1 ·
I didn't get a response in the Chevy section, so I'll post this here.

I've got a 1999 Vortec 5.7 with the MPFI injector spider in my Jeep. A few weeks ago it started to get harder and harder to fire up. Last week it didn't even try to fire up; it just turned over. I finally got around to checking the fuel pressure and found 52psi at the fuel rail. I replaced the external frame-mounted fuel pump with a new 100psi unit from Summit. Now I've got a question.

I'm seeing 100psi at the fuel rail (obviously). Can I rely on the injection system's pressure regulator to bring it down to the necessary 60-65 psi or do I need a regulator before the fuel rail? Are there any negative side effects to having 100psi at the fuel rail?
 
#2 ·
First off you should check in to replacing the injector spider. They go bad, get all gummed up and clog.
 
#3 · (Edited)
As I said, I replaced the stock spider with the MPFI spider. It's about 2 years old and I'm pretty sure it's not gummed up or clogged.

A bad spider doesn't have anything to do with my question anyway. Assuming everything is working properly, is 100psi at the fuel rail acceptable or do I need to bring it down to 65 psi for the motor's pressure regulator to work with?
 
#6 ·
You should not be seeing a 100psi at the fuel rail--it should be regulated closer to 60 by the fuel regulator. The only way it should hit 100psi is if the regulator is bad or you have a restriction in your fuel return line.
 
#7 ·
I called a buddy that's had a bit of experience with fuel injection systems. He's go the same thoughts. The regulator should send enough fuel back to the tank to keep the feed pressure down to 65. Is it possible that the regulator can't handle the volume that the pump flows? My new pump is rated for 80gph free flow, 100psi max pressure.
 
#9 ·
Alright. I popped the return line just before the tank and drained it into a bucket while running the motor. Fuel pressure stayed below 65 psi. I blew into the line heading to the tank and could hear bubbles, so I figured there wasn't anything blocking the line. I'm stumped about the high pressure.

I did find another issue during this test, though. I noticed that the fuel I drained into the bucket had an orange tint. The Jeep has been sitting for a month or two, so it looks like the fuel went bad. I drained the whole tank, dropped it from the Jeep, and removed the fuel sending unit.

I found a torn sending unit seal, some metal shavings in the bottom of the tank, and found that the little rubber piece that's supposed to be attached to the end of the return line was rolling around at the bottom of the tank. Not sure where the shavings came from or how the rubber piece came off the return line. I don't think the shavings came from the fuel pump since they would have been caught in the fuel rail's screen filter and wouldn't make it back to the tank.

I blew in the return line and felt no restriction, so no issues there. I'll clean out the tank put in a new sending unit seal, a new fuel filter, and fresh fuel. We'll see how that works out.

Anything I may have missed?
 
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