Fuel Pressure Regulator?
06-01-2015, 04:24 PM
#1
Senior Member
Thread Starter
Fuel Pressure Regulator?
1996 4.9L
My truck's having trouble starting occasionally. Good spark and compression, so I'm thinking a fuel pump or fuel pressure regulator. I have codes P0171 and P0174, bank 1 lean and bank 2 lean. It seems that the trouble starting is worse when the engine is hot, but it hasn't been going on long enough to confirm that for sure.
Fuel pressure:
Front tank engine off, turning key to on: 30psi
Rear tank engine off, turning key to on: 24psi
Front tank running: 37psi
Rear tank running: 28 psi
I know these are very low, the spec is 45-60psi.
When I take the vacuum line off of the fuel pressure regulator, pressure doesn't change a bit. This makes me think that the FPR is bad. Also, before the problem I had the FPR off and ripped an o ring, so I had to replace it. The ones I used look a tiny bit small, but they seemed to fit tightly. It's possible they're leaking though, but I don't think so. I've seen pictures of FPRs with a plastic washer instead of an o ring. Here's a picture of mine. What do you guys think? Are there any more tests I should do? Thanks a lot.
My truck's having trouble starting occasionally. Good spark and compression, so I'm thinking a fuel pump or fuel pressure regulator. I have codes P0171 and P0174, bank 1 lean and bank 2 lean. It seems that the trouble starting is worse when the engine is hot, but it hasn't been going on long enough to confirm that for sure.
Fuel pressure:
Front tank engine off, turning key to on: 30psi
Rear tank engine off, turning key to on: 24psi
Front tank running: 37psi
Rear tank running: 28 psi
I know these are very low, the spec is 45-60psi.
When I take the vacuum line off of the fuel pressure regulator, pressure doesn't change a bit. This makes me think that the FPR is bad. Also, before the problem I had the FPR off and ripped an o ring, so I had to replace it. The ones I used look a tiny bit small, but they seemed to fit tightly. It's possible they're leaking though, but I don't think so. I've seen pictures of FPRs with a plastic washer instead of an o ring. Here's a picture of mine. What do you guys think? Are there any more tests I should do? Thanks a lot.
Last edited by tvand13; 06-01-2015 at 04:35 PM.
06-01-2015, 04:39 PM
#2
1994 F150 XLT 5.8L 2wd
If you have a vacuum pump then apply vacuum to the line going to the FPR, it should hold vacuum. If you don't have a pump then you "could" suck on it but I would vote for borrowing a VP. Also when you remove the line do you notice a gas smell or fuel in the FPR vacuum line.
Does this issue happen with both tanks? It's possible for both pumps to go bad but not very likely, if it's both tanks and the above test passes then you may want to start with the fuel filter, it's cheap and easy to swap compared to replacing a pump. Plus if it looks old then it's probably due to be changed anyway.
And I may be wrong but FP for anything without the inline high pressure pump should be 35-45psi.
Does this issue happen with both tanks? It's possible for both pumps to go bad but not very likely, if it's both tanks and the above test passes then you may want to start with the fuel filter, it's cheap and easy to swap compared to replacing a pump. Plus if it looks old then it's probably due to be changed anyway.
And I may be wrong but FP for anything without the inline high pressure pump should be 35-45psi.
06-01-2015, 05:08 PM
#3
Senior Member
Thread Starter
When it doesn't want to start, neither tank will work. I'll just have to wait a little bit then try again. Cycling the key to make the pump run a few times before starting doesn't seem to help start it either.
I replaced the fuel filter with a Purolator 8000 miles ago. It could be plugged, but I don't think so.
The FPR vacuum line has a really faint fuel smell, not strong at all. I put a piece of clear tube in place of the vacuum line to see if I could see fuel leaking through the diaphragm through the tube. I couldn't see fuel running through it or anything, but after idling for a bit there were tiny droplets and the line smelled a little bit like fuel. I think I have a bad FPR, but I want to make sure before replacing it. I can get a vacuum pump right now. Thanks!
My Haynes says the EFI V8s are 30-45, but the EFI 4.9 is 45-60 running.
I replaced the fuel filter with a Purolator 8000 miles ago. It could be plugged, but I don't think so.
The FPR vacuum line has a really faint fuel smell, not strong at all. I put a piece of clear tube in place of the vacuum line to see if I could see fuel leaking through the diaphragm through the tube. I couldn't see fuel running through it or anything, but after idling for a bit there were tiny droplets and the line smelled a little bit like fuel. I think I have a bad FPR, but I want to make sure before replacing it. I can get a vacuum pump right now. Thanks!
My Haynes says the EFI V8s are 30-45, but the EFI 4.9 is 45-60 running.
06-01-2015, 08:03 PM
#4
Get a new FPR and retest. Fuel pressure on the 4.9 changed in mid 94 to 30 to 45 psi, same as the v8's.
But your pressure is still way low. The thing is it will run between 30 and 45, but at your pressures, not very well.
The thing is that injectors need pressure to spray, at the kind of pressure you have it gets more dribble like.
It could well be an issue with the FPR. Keep your fingers crossed !
Or a faulty check valve in one of the pumps, or a combination. But if you have any fuel smell in the vac line, you definitely need a new FPR, so start there.
But your pressure is still way low. The thing is it will run between 30 and 45, but at your pressures, not very well.
The thing is that injectors need pressure to spray, at the kind of pressure you have it gets more dribble like.
It could well be an issue with the FPR. Keep your fingers crossed !
Or a faulty check valve in one of the pumps, or a combination. But if you have any fuel smell in the vac line, you definitely need a new FPR, so start there.
10-24-2021, 10:56 AM
#5
10-24-2021, 02:10 PM
#6
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The Ford service manual says:
« 1996 Bronco/F-Series Table of Contents » « Group 10: FUEL SYSTEM » « Section 10-00: Fuel System, Service » FUEL PRESSURE SPECIFICATIONS
Engine Condition - - - - - - - - - - - 4.9L - - - - - - - - - - - 5.0L - - - - - - - - - - - 5.8L - - - - - - - - - - - 7.3L - - - - - - - - - - - 7.5L
Engine Running - - - - - - - - - - 45-60 psi - - - - - - - 30-45 psi - - - - - - - - 30-45 psi - - - - - - - 41-55 psi - - - - - - - 30-45 psi
. . . . . . . . . . . . . . . . . . . . . . 310-415 kPa . . . . . 210-310 kPa . . . . . . 210-310 kPa . . . . . 283-379 kPa . . . . . 210-310 kPa
Key ON Engine OFF - - - - - - 50-60 psi - - - - - - - 35-45 psi - - - - - - - - 35-45 psi - - - - - - - - - - - 0 - - - - - - - - - 35-45 psi
. . . . . . . . . . . . . . . . . . . . . . . 345-415 kPa . . . . . 240-310 kPa . . . . . . 240-310 kPa . . . . . . . . . . 0 . . . . . . . . . 240-310 kPa
Engine Condition - - - - - - - - - - - 4.9L - - - - - - - - - - - 5.0L - - - - - - - - - - - 5.8L - - - - - - - - - - - 7.3L - - - - - - - - - - - 7.5L
Engine Running - - - - - - - - - - 45-60 psi - - - - - - - 30-45 psi - - - - - - - - 30-45 psi - - - - - - - 41-55 psi - - - - - - - 30-45 psi
. . . . . . . . . . . . . . . . . . . . . . 310-415 kPa . . . . . 210-310 kPa . . . . . . 210-310 kPa . . . . . 283-379 kPa . . . . . 210-310 kPa
Key ON Engine OFF - - - - - - 50-60 psi - - - - - - - 35-45 psi - - - - - - - - 35-45 psi - - - - - - - - - - - 0 - - - - - - - - - 35-45 psi
. . . . . . . . . . . . . . . . . . . . . . . 345-415 kPa . . . . . 240-310 kPa . . . . . . 240-310 kPa . . . . . . . . . . 0 . . . . . . . . . 240-310 kPa
10-25-2021, 11:33 AM
#7
On a related note.... Are the 2-bolt 4.9 and V8 FPR's physically interchangeable? i.e. If for some reason I wanted to run my V8 with 60 PSI could I just use a 4.9 spec FPR? Don't worry about the software/tuning issues - I'm aware of that. I'm actually only wanting to do this on a temporary basis as a diagnostic tool.
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10-25-2021, 11:53 AM
#8
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I wouldn't know. I've used the fuel pump from a V8 Bronco in my 4.9L Bronco for decades, and it makes a steady 35psi, which will run my overweight Bronco above 100mph for as long as I want (and I have the tickets from doing it).
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