Fuel pressure leak!

hey everyone. i have a 95 b4000 4.0l v6 sohc. fuel pressure when running is 30psi. and fuel pressure when i turn it off is at about 35psi and after about 30 mins it leaks to about 6psi and it stays there. after sitting overnight it has a VERY hard time starting. it barely starts. sounds like a really bad miss until it gets going normal again. what could this be? where could all my pressure be going? thanks.

If you don't smell gas then there are 3 places for pressure to leak out on a '95

1. Fuel Pressure Regulator(FPR), it is on the top of lower intake, passenger side front.
It will have the Return Fuel line connected and a vacuum hose.
It has a diaphragm inside with a spring to hold it closed when engine is off.
Spring could be weak or diaphragm is leaking fuel and it is going back to the gas tank.

2. Fuel pump check valve, this is part of the fuel pump, basically just a flap that is pushed open when fuel pump is on and then closes when pump is off to hold pressure in the system.

3. A Fuel injector can't close all the way so leak fuel into intake when engine is off, you should notice drop in MPG with this, and/or blackish smoke when you start engine after it sits for 30minutes, longer than that and most of the fuel would evaporate.
You could run some Seafoam or similar injector cleaner in the gas tank to clean out any debris.

If you are careful you can clamp return fuel line, don't crush it, just clamp it after you shut it off the engine.
See if pressure holds
If so replace FPR
If it still drops then most likely fuel pump needs to be changed.

For the time being turn on the key 3 or 4 times before a cold start, that will cause the fuel pump to run 6 to 8 seconds, 2 seconds each time key is turned from off to on, that will build up the lost pressure so it will start easier.


There is a 4th place, which is the fuel line from the pump to the top of the gas tank, if it is leaking then fuel pressure would go down after shut off and fuel would just leak out of line and into the gas tank.

RonD said:

If you don't smell gas then there are 3 places for pressure to leak out on a '95

1. Fuel Pressure Regulator(FPR), it is on the top of lower intake, passenger side front.
It will have the Return Fuel line connected and a vacuum hose.
It has a diaphragm inside with a spring to hold it closed when engine is off.
Spring could be weak or diaphragm is leaking fuel and it is going back to the gas tank.

2. Fuel pump check valve, this is part of the fuel pump, basically just a flap that is pushed open when fuel pump is on and then closes when pump is off to hold pressure in the system.

3. A Fuel injector can't close all the way so leak fuel into intake when engine is off, you should notice drop in MPG with this, and/or blackish smoke when you start engine after it sits for 30minutes, longer than that and most of the fuel would evaporate.
You could run some Seafoam or similar injector cleaner in the gas tank to clean out any debris.

If you are careful you can clamp return fuel line, don't crush it, just clamp it after you shut it off the engine.
See if pressure holds
If so replace FPR
If it still drops then most likely fuel pump needs to be changed.

For the time being turn on the key 3 or 4 times before a cold start, that will cause the fuel pump to run 6 to 8 seconds, 2 seconds each time key is turned from off to on, that will build up the lost pressure so it will start easier.


There is a 4th place, which is the fuel line from the pump to the top of the gas tank, if it is leaking then fuel pressure would go down after shut off and fuel would just leak out of line and into the gas tank.

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ron. it had a brand new pump and assembly in it. even if i cycle the key 3 or 4 times and still has the super rough and or no start issue. but ONLY after sitting overnight. after its ran it starts right away. i have been battling this for some time now and nobody knows.. i will check the fpr in a bit. very frustrated. somebody has had to have this problem before if anyone can chime in please do.

Hook up pressure gauge after it sits over night.
Then cycle the key on to see how much pressure you are getting, then repeat, key off and on.
Until you get up to 30psi
Then try to start engine

If it still struggles then air is being pulled into the system(fuel rail) when it sits, so while you are getting enough pressure in the system the air must be purged out before fuel can take its place and engine runs smoothly.
This would mean a small external fuel leak, most likely on or near fuel rail.

Start cold engine, after it is running ok shut it down and wait 10 minutes or so, then start running your fingers around injectors and fuel lines feel for fuel and smell for fuel

RonD said:

Hook up pressure gauge after it sits over night.
Then cycle the key on to see how much pressure you are getting, then repeat, key off and on.
Until you get up to 30psi
Then try to start engine

If it still struggles then air is being pulled into the system(fuel rail) when it sits, so while you are getting enough pressure in the system the air must be purged out before fuel can take its place and engine runs smoothly.
This would mean a small external fuel leak, most likely on or near fuel rail.

Start cold engine, after it is running ok shut it down and wait 10 minutes or so, then start running your fingers around injectors and fuel lines feel for fuel and smell for fuel

Click to expand...

ron, if it is leaking through my injectors after 30 mins, after its ran and warmed up, how come it starts fine then but not in the morning after its sat all night? also i cant block off my return line because its that flexible metal hose. any ideas?

Return fuel line should be rubber hose with metal braid over it.

Reason it starts OK within an hour or two is because there would still be fuel in the fuel rail, lower pressure but fuel none the less, as soon as engine RPMs get to 400 fuel pump comes on full time so you wouldn't notice the lower pressure too much.

I am just assuming from your description, after turning key on and off 3 or 4 times, and still getting no start or stumbling start that problem is air in the fuel rail coming in from fuel leaking out and over time air being pulled in to replace the leaking fuel.
Just a guess.
Based on fuel pressure dropping over first 30 minutes.
It could also be same situation but in the gas tank, leaking hose/line allows fuel pressure to go down then gravity leats more fuel drain off and it is replaced with air, so now you have air in the lines, although I would expect a good start and then a stumbling as the air was forced from tank to engine.


There is another test you can do, for leaky injector.
Shut warmed up engine off
turn on the key
press gas pedal to the floor and hold it down all the way

Key ON, engine OFF, gas pedal to the floor = Clear Flooded Engine routine in the computer
Computer will shut off Fuel injectors but leave spark on.

Leaving gas pedal all the way down try and start engine
it should NOT start, it should not even fire since there is no fuel coming in
If it does fire then fuel is getting in.

If it does fire, next test would be to let the engine sit for 10 minutes.
Unplug the coil pack, so no spark
Do same test as above, gas pedal to the floor, crank it a few times
Now pull spark plugs
Wet spark plug has the leaking injector

I have had warm engines without leaking injectors start while supposedly in clear-flood. That isn't the most reliable test. It doesn't take a lot to get a warm engine started, residual vapor from shutdown in the intake can do it, and once the engine catches the clear-flood strategy isn't used.

A more reliable, but more involved, test for leaking injectors is to pull the injectors and the rail, get the injectors secured (will involve zip ties) and then pressurize the system. The leaker will drip.

A return style fuel system will naturally loose pressure when the pump is off, and can go as low as 5 PSI static, but if it is going down the return line the system should pressurize instantly when the pump is turned on again. If the leak is external one of two things can happen.

1) It will draw air in, and make it hard to build pressure.

2) If it is an injector it can flood a cylinder, and that will make it miss and carry on, and possibly cause a hard start. If this happens one of two other things also generally happens. The cylinder will hydrolock, or the fuel will end up in the oil. Check, and smell, your oil.

well i was going to shoot a little video for yall to show yall exactly what its doing. but i went to crank it thismorning and she decided to behave today and fired right up.. but i promise you shes just in a good mood today. ill get the video for yall tomorrow morning. seing it for yourself would help explain it alot better. thank you for all the help so far though.

i need a quick answer here guys. so on my fuel rail there are 2 metal coated rubber tubes. one on the front of the rail and one on the back (firewall) witch is witch and witch side is the regulator on?? i believe its on the front side right?? also when i jiggle the back fuel line around my fuel pressure guage spazzes out. is this normal. thanks

Yes, Fuel lines are rubber but have braided metal mesh around them

IN fuel line is on drivers side toward the back of engine, connected to fuel rail.
Return line is on Passenger side toward the front of the engine, connected to FPR.

Pressure should not change if you "jiggle" either hose, you may have found your problem, connector is lose

i stuck my camera up in there and where the IN fuel line connects to the rail i can see threads like maybe the connectors not screwed all the way on. ill see whats up with it and let yall know. the fpr is fine. just pinched the line and it still leaked

RonD said:

Yes, Fuel lines are rubber but have braided metal mesh around them

IN fuel line is on drivers side toward the back of engine, connected to fuel rail.
Return line is on Passenger side toward the front of the engine, connected to FPR.

Pressure should not change if you "jiggle" either hose, you may have found your problem, connector is lose

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ok so heres where im at. its not the fpr, its not the line connecting to the rail. and at the slow rate that it leaks to 0psi (about 20-30 mins) im not sure if its the check valve or not. im leaning towards that but more towards injectors because of the hard start condition i have after it sits overnight. but like i said after its warm it starts fine after sitting for a while. what do yall think.

So after it sits overnight, hook up pressure tester and cycle the key on and off a few times, don't try to start engine.
See what the pressure is, cycle key on and off as needed to get it up to 30-40 psi.

Now remove the gauge and carefully push in the pin on a schrader valve, fuel can squirt out 30ft so be careful, see if there is air or fuel inside

RonD said:

So after it sits overnight, hook up pressure tester and cycle the key on and off a few times, don't try to start engine.
See what the pressure is, cycle key on and off as needed to get it up to 30-40 psi.

Now remove the gauge and carefully push in the pin on a schrader valve, fuel can squirt out 30ft so be careful, see if there is air or fuel inside

Click to expand...

ron. it goes up to 35psi, where it should, in one key cycle in the mornings. i checked thismorming. i will try seeing the air/fuel mixture in the rail tomorrow morning. hopefully i can catch the hard start on video tomorrow.