What is the normal fuel pressure at the rail?

[Sparkles254]

I have a 96 explorer 4.0. Using a harbour freight guage I'm showing 29 psi. After the outside temperature reaches 92 degrees my vehicle starts idling very rough and the guage reads 10 psi. So I know I'm having fuel related issues for sure now. I would just like to know what the normal pressure is supposed to be.

 

[koda2000]

for a '96 about 35-37 PSI at the rail

 

[Sparkles254]

With the fuel pressure being low and then dropping after it gets hot, is this definitely a bad fuel pump or could it be a relay or something else?

 

[koda2000]

Fuel pump.

 

[gatzdon]

FYI, with a Bluetooth OBD2 reader and Forscan, you can get the fuel pressure straight from the computer in real time. No gauges needed.

 

[fastpakr]

Are you sure? I don't remember seeing that as a possible meter to add .

 

[410Fortune]

the 96 PCM does not monitor fuel pressure
29 psi is toooooo low your injectors will drip fuel instead of a nice atomized spray

 

[CDW6212R]

Ditto, 30 psi is about the low point that you know it's the pump or a clogged fuel filter. 32psi should be the normal lowest pressure, when the vacuum line is taken off the FPR, the pressure should jump to near 40psi.

If the filter hasn't been changed in a while, do that first and pour the old gas from the inlet side. See how dirty/full the filter is, if it's bad enough the pump might still be okay.

 

[imp]

the 96 PCM does not monitor fuel pressure
29 psi is toooooo low your injectors will drip fuel instead of a nice atomized spray

@410Fortune @Sparkles254

I suspect reading fuel pressure by the PCM began with returnless fuel system, 3rd. gen, not certain of year, or possibly very late in 2nd gen. No matter when, '96 did not. imp

 

[RandomNerd2000]

I'd try the filter. My 2000 had an issue develop where it hesitated and acted bogged down, like it was running out of gas. Turns out the filter clogged up, I released the pressure at the rail, got the tool, and then proceeded to get a pressurized gas bath from the input side of the filter...

To recap, a clogged filter is possible, although my money is on your pump. Also, they want a matched receipt for the pump and filter for warranty, no filter? No warranty.

@imp It's definitely not 2nd Gens, my 01 does NOT read fuel pressure in the PCM.

 

[imp]

@imp It's definitely not 2nd Gens, my 01 does NOT read fuel pressure in the PCM.

@RandomNerd2000

I just don't know which year went returnless, but think it may not have been 2002. My 2004 is returnless, and measures both fuel pressure and temperature by a single sensor mounted on the rail. And, it's a ***** to get at! Replacement went bad in 6 months. 2nd. replacement still good, couple years now. That sensor tells the pump indirectly how fast to run. My worry was being stranded. FWIW, if Fuel Pressure & Temperature Sensor fails totally, engine keeps running, but very rich, full pump output to rail constantly, ~ 100 psi. imp

 

[fastpakr]

Returnless happens in 98 I recall. Definitely by 99.

 

[RandomNerd2000]

99-Up is returnless.

 

[410Fortune]

half way through 98 they went returnless, unless you are a Sport trac then it stayed return in 2001.....fun!

Always replace the pump STRAINER and filter at the same time
Use a good quality pump like Bosch or Carter otherwise you will be doing the job again soon

 

[koda2000]

half way through 98 they went returnless, unless you are a Sport trac then it stayed return in 2001.....fun!

Always replace the pump STRAINER and filter at the same time
Use a good quality pump like Bosch or Carter otherwise you will be doing the job again soon

Not true. I've owned multiple 2000's and 2001's. All are return-less including my 2001 Sport Trac. I believe '99 was return-less also. IDK about '98, but I do know that '97 was a return-style system.

Note: My late production '01 ST had a second line connected to the tank, but it only went as far as the 3-port fuel filter (not sure of the purpose of this). The in-tank fuel pump assembly in my ST still has the FPR above the fuel pump just like the return-less Explorers.

 

[donalds]

I believe they switched in 98
I used a carter pump
Working great so far

 

[koda2000]

I tried 1 AirTex fuel pump (mistake - lasted about a year <10k).

All the other pumps I've installed (at least 6) were Bosch. All have worked perfectly. Most were PN 69128 fuel pump kits, which come with new submersible hose, FI clamps, pump isolator and plug-and-play jumper wire. Only other things needed were the strainer sock and fuel filter. I couldn't be happier with the Bosch pumps.

The Bosch pump kit is currently around $44 on eBay with free shipping.

 

[donalds]

Not to bad to replace the pump don't even need to remove the tank all the way or the pesky fuel lines

I however replaced the whole sender because of a suspect fuel pressure regulator on the sender on my 99

 

[imp]

FWIW, Ford used an in-line pump in F-150s around 1988. It was supposedly a "low-pressure" pump, used in conjunction with the in-tank "high-pressure" pump, Ford's nomenclature here. The in-line is a HUSKY pump, designed heavy to get rid of heat the in-tank disposed of by being submersed in liquid, instead of air.

I used the in-line pump when I did my first EFI conversion, 1970 Bronco w/ 5.0 HO Mustang engine. Worked admirably well, with only the in-line.

Same thing with 1979 Ranchero, in-line pump, 5.0 HO out of a Police car Mustang. Worked very well. Re-working an existing tank to retrofit a pump in it is B.S. I did that once for a customer who bought a 5.0 from me, installed it in his Toyota 1/2-ton. Managed to get a pump in the tank. ****, I'd never go that route again.

Both above conversions were return-type fuel, engines early 1990's. imp

 

[CDW6212R]

FWIW, Ford used an in-line pump in F-150s around 1988. It was supposedly a "low-pressure" pump, used in conjunction with the in-tank "high-pressure" pump, Ford's nomenclature here. The in-line is a HUSKY pump, designed heavy to get rid of heat the in-tank disposed of by being submersed in liquid, instead of air.

I used the in-line pump when I did my first EFI conversion, 1970 Bronco w/ 5.0 HO Mustang engine. Worked admirably well, with only the in-line.

Same thing with 1979 Ranchero, in-line pump, 5.0 HO out of a Police car Mustang. Worked very well. Re-working an existing tank to retrofit a pump in it is B.S. I did that once for a customer who bought a 5.0 from me, installed it in his Toyota 1/2-ton. Managed to get a pump in the tank. ****, I'd never go that route again.

Both above conversions were return-type fuel, engines early 1990's. imp

I know that feeling, "I'll never do that again." I haven't decided on how to make the fuel system for my old 72 Ranchero, with EFI and a 97 PCM.