Fuel Pressure
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Fuel Pressure
95 f250 5.8 4x4Fuel pressure 30lbs at ide, pull vacuum off it increases to 34lbs, still at idle.,Increase rpm to about 2500rpm, vacuum back on regulator, pressure max at 35 psi.,--- Am only getting 7 miles per gallon, could this be the problem., If so, how would a bad pressure regulator cause poor gas mileage??--God Bless,John
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From: Ottawa, Ontario
That pressure is low, it should be 40-45psi with vacuum off the regulator. Fuel pressure that low could contribute to bad milage by requiring you to work the engine harder to get around.. though if your 7mpg figure is accurate i suspect there is something else going on like fuel transfer between tanks or a leaky tank.
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That pressure is low, it should be 40-45psi with vacuum off the regulator. Fuel pressure that low could contribute to bad milage by requiring you to work the engine harder to get around.. though if your 7mpg figure is accurate i suspect there is something else going on like fuel transfer between tanks or a leaky tank.
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From: Omaha/or under my truck
Only have one tank operational, but also could a leaking brake booster cause that poor of a mileage?, I am 63 and hearing is shot but my daughter says she hears a major "hissing" when my brake is applied and sitting at a stop light, the hissing is located at the brake pedal., What would good vacuum be for this 5.8 with 220,000 mile., Compression is flat on 120 psi all around on all eight., Code engine on, "Egr no flow and Lean Hego", (close enough wording I guess., Thanks so very much.,God Bless,John
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,Thanks for the reply.,Would the vacuum leak cause the computer to give the engine more fuel (lean condition), causing mileage to drop?,Just trying to understand how it works!,Thanks,John
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From: Easton,Ks
30 psi is OK at idle.
A big vacuum leak will make the fuel pressure go up not down.
To get the 45psi fuel pressure you need the engine not running, pin #2 shorted to pin #6 of the self-test connector and turn on the key with the fuel pressure gauge hooked to the fuel rail. Some fuel pressure gauges that read 30psi at idle will only read 40psi during the test.
I also have a high dollar fuel pressure gauge that reads 45psi with the engine off and pins 2 to 6 jumped with the key on. It also reads about 34psi at idle. This is with the same truck as in the photos below.
The big vacuum leak she hears is a bad brake booster diaphragm and will cause high fuel pressure and poor gas mileage.
I would check the nipple of the Fuel Pressure Regulator (FPR) with the vacuum hose removed when you turn on and the off the key with a cold engine and see if any fuel comes out of the nipple. If any fuel at all comes out the FPR nipple it is bad.
2 to 6 jumped, engine not running:
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A big vacuum leak will make the fuel pressure go up not down.
To get the 45psi fuel pressure you need the engine not running, pin #2 shorted to pin #6 of the self-test connector and turn on the key with the fuel pressure gauge hooked to the fuel rail. Some fuel pressure gauges that read 30psi at idle will only read 40psi during the test.
I also have a high dollar fuel pressure gauge that reads 45psi with the engine off and pins 2 to 6 jumped with the key on. It also reads about 34psi at idle. This is with the same truck as in the photos below.
The big vacuum leak she hears is a bad brake booster diaphragm and will cause high fuel pressure and poor gas mileage.
I would check the nipple of the Fuel Pressure Regulator (FPR) with the vacuum hose removed when you turn on and the off the key with a cold engine and see if any fuel comes out of the nipple. If any fuel at all comes out the FPR nipple it is bad.
2 to 6 jumped, engine not running:
/
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From: Ottawa, Ontario
By operational do you mean the tank is still there but the pump doesn't work? If so there could still be a problem, fuel transfer between tanks is very common and it happens when the check valves in the FDM inside the tank get stuck upen with age or dirt and allow the working tank to pump fuel into the other while you drive, and once the tank is full it will overflow onto the ground. Do you have a raw fuel smell around the truck immediately after parking? This problem could also be the cause of your low fuel pressure.
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From: Ca.
I installed an Autometer digital fuel pressure gauge in the dash. It cost about $250 from Summit. Was able to diagnose things with that.
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By operational do you mean the tank is still there but the pump doesn't work? If so there could still be a problem, fuel transfer between tanks is very common and it happens when the check valves in the FDM inside the tank get stuck upen with age or dirt and allow the working tank to pump fuel into the other while you drive, and once the tank is full it will overflow onto the ground. Do you have a raw fuel smell around the truck immediately after parking? This problem could also be the cause of your low fuel pressure.
' Other tank was removed by PO and the pump etc, from that tank the PO left it in place attached to the frame "tied up" and I have not had a chance to remove it yet and yes I do have a raw fuel smell after I park it overnight!If I have just the one tank, what is the best way to remove all it's accessories John(fuel pump, etc
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From: Ottawa, Ontario
What you need to do is plug the fuel lines(both) where they attach to the pump assembly, I made plugs for this exact purpose from old engine water pump studs, simply cut them down and ground the heads so the fuel line retainer clips could be used to keep them in place. This worked perfectly for over a year and never leaked, and note that the send and return lines are different sizes.
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What you need to do is plug the fuel lines(both) where they attach to the pump assembly, I made plugs for this exact purpose from old engine water pump studs, simply cut them down and ground the heads so the fuel line retainer clips could be used to keep them in place. This worked perfectly for over a year and never leaked, and note that the send and return lines are different sizes.
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' Thanks so much and I will keep you posted.,Is there any way to check this or can I just start the engine, crawl under and inspect. Once a "check valve" fails is it intemittent or is it bad all the time usuallly?,John
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I removed the lines from the "hanging" fuel pump and gas poured from one of the lines, guess it is the return line colored (blue). No gas should come from a tank line which is not switched and therefore the "check valve" in the good tank is bad, CORRECT? Which is the return?Getting ready to plug them per Conasnki.God BlessJohn