WTF is my fuel pump going bad

just4bob50

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#1

• Aug 11, 2005

• #1

Ive only noticed this problem in the last couple of weeks. At first I thought it was my crappy MAC reg, but I replaced it with an Aeromotive one and I still have the problem. when the car starts up in the morning my base fuel pressure is aroung 44-45psi. when the car gets to operating temp it falls back to 40 psi. which is where i set the base pressure. I drive 20miles to work and check pressure and it fine, but if I take the car out for a beating on some back roads after a few blasts through the gears the car starts to feel slugish up top. when i pulled over to check my fuel pressurthe base psi was down to 34-35psi. So I take it easy on the car on the way home and check pressure again and its back to 40psi. This has been happening for the last few days as i have been doing this routine repeatedly to make sure it is the same problem evrytime. I have a 190 pump in, but it is used. Im wondering if the pump is heating up and not working right or is just about to crap out. Either way the car is fine driving it normally, but after a few high rpm runs it starts to lay down on the top end.

 

jrichker

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#2

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• #2

Best thing to do is to measure the voltage at the pump wiring. If you installed the pump, remember the two wire connector that had the black & pink wires? Use a DVM and check the voltage between the pink wire and ground. Check the black ground wire to make sure it is bolted to a clean shiny bare metal spot on the body.

Once you have eliminated the electrical power delivery to the pump, then start chasing the other possible sources of decreasing fuel pressure.

 

bubba-dough

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#3

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jrichker gives some good advice. electrical problems can be deceiving. I'm not very knowledgable with fuel systems but my g/f has a SVT Contour and her car was doing the same thing earlier this year. We took it to the dealer and it was the fuel pump going bad and the throttle plates had to be cleaned. The car runs like a champ now.

 

1991vert

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Feb 27, 2004

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#4

• Aug 11, 2005

• #4

doesnt the computer somehow set it back to around 40 psi, no matter what?

when your fuel pump is on it's way out they usually whine A LOT louder than normal. i found a brand new walbro 255lph for $80. i'd buy a new one if you diagnose it as the problem and be set for future mods

 

QDRHRSE

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#5

• Aug 11, 2005

• #5

Change your fuel filter...its cheap, easy, and probably couldn't hurt anyway. How much gas do you typically keep in the car? I agree with the diagnostic approach but from personal experience I have found that 90% of the time if you change the filter and make sure the tank has plenty of gas in it all the problems go away. It is really important to keep a lot of fuel in the tank because the fuel is what keeps the pump cool. A lot of people go to the gas station and put in $10 at a time- those are usually the people that complain that they go through fuel pumps....like my brother in law. Some times if its hot and you are really low on gas the pump can overheat. If the filter is clogged the pump pressure will drop and the pump gets hot as well. Try it out!

 

jrichker

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#6

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1991vert said:

doesnt the computer somehow set it back to around 40 psi, no matter what?

when your fuel pump is on it's way out they usually whine A LOT louder than normal. i found a brand new walbro 255lph for $80. i'd buy a new one if you diagnose it as the problem and be set for future mods

Click to expand...

The computer does not sense fuel pressure on 5.0 stangs. The newer cars with a returnless fuel system do use a pressure sensing sensor. That enables them to not have a return pipe or a mechanical fuel pressure regulator.

 

just4bob50

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#7

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QDRHRSE vbmenu_register("postmenu_5372151", true); As coinsidence would have it, last night when the problem was the worst its been. I only had an 1/8 tank of fuel and ive only been putting 20$ in at a time because of gas prices being high. what you say kinda makes sense.

 

QDRHRSE

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#8

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• #8

I've had a lot of Mustangs.....change the fuel filter and keep it full. Maintanence never hurts!

 

just4bob50

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#9

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QDRHRSE the only 2 things that i didnt do my self were the clutch, and fuel pump. Im guessing I have to drop the tank to change the filter. If I do have to drop the tank is it worth putting a bigger pump in while the tank is down.

 

tunedin302

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#10

• Aug 11, 2005

• #10

jrichker said:

If you installed the pump, remember the two wire connector that had the black & pink wires? Use a DVM and check the voltage between the pink wire and ground. .

Click to expand...

Good advice. I had that connector go bad on me when I did my fuel pump. Ended up taking that connector out and hard wiring my pump. Good ever since.

 

Euphoric306

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#11

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• #11

the fuel filter is in front of the fuel tank... just follow the fuel lines, u cant miss it... no need to drop the tank, just relieve fuel pressure (its a good idea to do first) and then unclip the fuel lines, set ur new filter in place, connect lines, reset pressure, and ur good to go


to relieve pressure, find the inertia switch, should be in trunk or hatch, and unplug it. to reset pressure, plug back in and press the button on it.

sounds more like ur filter than a pump, because like 1991vert said, itd be making a lot louder whining if it was going out

qdrhrse was right about the cooling issue too... ur pump will last a lot longer AND u get better gas mileage if ur tank is always on the full side

 

just4bob50

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#12

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Thanks for all the info guy's

 

K

kystang1889

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#13

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...

 

B

black92gt

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#14

• Aug 11, 2005

• #14

My fuel pump does almost the exact same thing, and I was wondering what the problem might be. Mine runs like a bat out of **** the first few times, after that it craps out after 4k rpm.

 

just4bob50

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#15

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I just put in a new fuel filter tonight. The one that was replaced was the original, and my car has just over 100,000 miles on it. I took it out for a drive and the slight stumbling i sometimes felt is gone. Unfortunatly it rained really hard tonight and i was not able to really pound on the car. I hope this is it because every other part of my fuel system is new except for the pump.