Fuel Pump
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Fuel Pump
Ok, i need help,
I'm working on my mother-in-laws 99 expedition, 5.4L,
The problem is fuel pressure, the car died and wouldn't start back and was towed home and i couldn't hear the fuel pump kicking in at all and of course there were no codes when i checked, i checked the fuse and relay and wasn't getting any fuel on the rails so i changed the fuel pump. The first pump i put in would hum when the key was turned on, but still no fuel on the rail so i took the fuel hose loose on the engine side of the fuel filter and got no gas, so i changed the pump again and the fuel filter, now i get gas at the rail and the car will start and idle but will sputter and stall under any ammount of load. I seem to be getting around 15-20 psi at the rail and i know i should getting around 50-55, my question is, is there anything else that can cause the pump not to push enough pressure, or am i going to have to replace the fuel pump yet again.
I'm working on my mother-in-laws 99 expedition, 5.4L,
The problem is fuel pressure, the car died and wouldn't start back and was towed home and i couldn't hear the fuel pump kicking in at all and of course there were no codes when i checked, i checked the fuse and relay and wasn't getting any fuel on the rails so i changed the fuel pump. The first pump i put in would hum when the key was turned on, but still no fuel on the rail so i took the fuel hose loose on the engine side of the fuel filter and got no gas, so i changed the pump again and the fuel filter, now i get gas at the rail and the car will start and idle but will sputter and stall under any ammount of load. I seem to be getting around 15-20 psi at the rail and i know i should getting around 50-55, my question is, is there anything else that can cause the pump not to push enough pressure, or am i going to have to replace the fuel pump yet again.
Tuned
Joined: Jul 2007
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From: So. Cal.
There might be a better answer than this but I had a similar happening and it turned out the tank had lots of stuff in it that kept clogging the fuel filter and the one in the tank too. It seems like if this were the problem it would still build pressure at the rail if the pump is allowed to run for long enough with the engine off. Try cycling the key a number of times while looking at pressure. Also maybe pressure regulator is letting the pressure escape.
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well it doesn't build up enough pressure to begin with, but the pump also only runs for 3 seconds then it powers off, even when the key is on and i hit the scrader valve and release pressure, the pump doesn't kick back on but i'm not sure if it should or not, i thought it was supposed to keep pressure in the line
Tuned
Joined: Jul 2007
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From: So. Cal.
Yes that short period the fuel pump runs is supposed to charge the fuel sys to the proper pressure and hold it there after the pump stops. If you have restricted flow to the fuel rail somewhere the short period the pump runs may not be enough time to build the pressure at the reduced flow rate. I think the pressure should be somewhere near 40 psi. I've seen some pressure at the schrader where if you push the schrader in the fuel squirts out around 6 inch or so and the engine won't start. When the pressure is what it's supposed to be it squirts out real good like 3 feet or more.
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I was thinking it may be the fuel pressure regulator, but to be honest i don't know how to check one to see if its good, anyone have any advice, and yes thats what happens on the fuel rail, it squirts around 4-6 inches no matter how many times i turn the key on and off so it never builds up enough pressure
Tuned
Joined: Jul 2007
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From: So. Cal.
A quick test that doesn't really give enough info without a test pressure gage is to put vacuum to the pressure regulator. If it doesn't hold vacuum it's bad. Other than that it's supposed to give High fuel pressure at no vacuum and low fuel pressure at high vacuum. Something you can do to eliminate the possibility that it's letting the pressure past it is to pinch off the fuel line after the regulator before it goes into the fuel tank. Better to block it off because pinching a hose can damage the inner lining. Then see if the fuel squirts real good. Be carefull with that gas all over the place.
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Tuned
Joined: Jul 2007
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From: So. Cal.
Forgot to say that the regulator is most likely mounted on the fuel rail and that it probably is vacuum controlled. The pinch off test will work weather it vacuum controlled or not. If you get good pressure with the line pinched off then the regulator is letting the pressure past it when it shouldn't.
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Correct on both counts. Also, be aware that there is a return fuel line. The regulator does it's job by allowing fuel to pass it and return to the tank via this return line. If the FPR is allowing fuel to leak passed it, then you will not get the fuel pressure you're supposed to get.
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One other thing I think would be worth checking is the electrical connection to the fuel pump. See if it is putting out the correct amount of voltage. Most likely this is not it but still worth checking in my opinion.
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ok, i tested the fuel pressure regulator and it still couldn't build enough pressure, went up to around 20 with it blocked off and the engine running, i think that the part is just the wrong part, this is what happens when you try to use inferior parts to save money. I am putting in a good part either tomorrow or the next day and i'll keep you guys updated, and thanks for all your help
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