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  1. #1

    Default Mechanical Fuel Pump Issues

    Hi all, I'm new to this forum and forums in general so bear with me.
    About a year ago I purchased an 86' Mustang LX with a 85' GT 5.0 with a 4 BBL and 5 speed transmission swapped in after the 85 was rolled in an accident. After about six months of ownership and the car running fine it refused to start. The car would turn over when gas was put directly into the carb so I figured it was an issue with the fuel pump/system. This past summer I replaced the mechanical fuel pump, the car ran for about a month and then refused to hold an idle while driving and when I got it back home it would not start up and still does not currently start up. I'm confused as to what could be causing this. The fuel lines themselves are tight, the mechanical fuel pump was installed correctly, but when the I try to put gas in the carburetor by pumping the throttle when the car is off no gas get's to the carb. I checked the stone fuel filter and it wasn't clogged either.

    Is there something I'm forgetting or missing here? I'm also willing to remove the mechanical fuel pump and replace it with an inline electric one mounted either in the engine bay or near the back on the frame to make startups in the future easier as well.

  2. #2
    Moderator wraithracing's Avatar
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    Since this car has been modified from its original setup there could be unusual issues causing the no start.

    First the 86 setup used a fuel filter at the back of the car just in front of the tank under the car. Is that still there and if so have you checked to make sure that fuel filter is not clogged up?

    Have you verified that you are getting fuel to the fuel pump? Is the fuel pump pumping fuel up the the carburetor?

    Are the carburetor fuel floats set correctly?

    Have verified that you have ignition and spark at the plugs?

    I would check all the simple and cheap stuff first to make sure what is the exact problem with the no start, is it fuel, spark, air, or compression? Miss one of those and the car will not start. Once you have answers to all of the above you should be able to narrow down what you are dealing with and if you still need help members here will be much more able to point you in the right direction. Good Luck!
    ​Trey

    "I Don't build it hoping for your approval! I built it because it meets mine!"

    "I've spent most of my money on Mustangs, racing, and women... the rest I just wasted."

    Mustangs Past: Too many to remember!
    Current Mustangs:
    1969 Mach 1
    1979 Pace Car now 5.0/5 speed
    1982 GT Stalled RestoModification
    1984 SVO Still Waiting Restoration
    1986 GT Under going Wide Body Conversion Currently

    Current Capris:
    1981 Capri Roller
    1981 Capri Black Magic Roller Basket Case
    1982 Capri RS 5.0/4spd T-top Full Restoration Stalled in TX
    1984 Capri RS T-top Roller
    1983-84 Gloy Racing Trans Am/IMSA Body Parts

  3. #3

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    I recently acquired a carburated foxbody and I have a local savant whom I run all my combinations by. First thing he said was to dump the mechanical fuel pump. The modern gas is brutal for them and he said it's even worse for an aftermarket pump. I'm sure other guys have had different results but for me as a car that sits for lengths of time it's the worst case scenario. His advise was to electric pump it and forget it.

    Sent from my SM-G892A using Tapatalk

  4. #4

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    Maybe there is crud in the gas tank that is getting sucked up and clogging things in the pump. Tanks are relatively cheap for these cars, due to the age, it might be worth it to swap in a new one. Good Luck with it and post your solution once you find it.

    Mike
    1982 GT 351W, retro hyd roller, ported Pro Comp heads, Tremec, M2300K brake kit, Recaros...needs paint!
    1984 LX 5.0 Vert *SOLD*
    1993 Cobra #3971 mostly stock *SOLD*
    1966 FFR Cobra replica 383W, Vic Jr heads, Vortech YS, TFS Box intake, 652rwhp, crazy fast!
    1987 GT in MM&FF May of 97 "Not Fade Away" white and purple. Sold 1999

  5. #5

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    Quote Originally Posted by brian.aughe View Post
    I recently acquired a carburated foxbody and I have a local savant whom I run all my combinations by. First thing he said was to dump the mechanical fuel pump. The modern gas is brutal for them and he said it's even worse for an aftermarket pump. I'm sure other guys have had different results but for me as a car that sits for lengths of time it's the worst case scenario. His advise was to electric pump it and forget it.

    Sent from my SM-G892A using Tapatalk
    Did you end up installing an electric one? If so which did you use?

  6. #6

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    I hadn't thought of there being another filter back at the tank since it was a carb and figured it would just be a stone filter. How would I verify I'm getting fuel to my pump? Just by cranking the engine?

  7. #7

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    Quote Originally Posted by alexpp361 View Post
    Did you end up installing an electric one? If so which did you use?
    Not yet but was thinking about the Holley sniper pump.

    Sent from my SM-G892A using Tapatalk

  8. #8
    Moderator wraithracing's Avatar
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    Quote Originally Posted by alexpp361 View Post
    I hadn't thought of there being another filter back at the tank since it was a carb and figured it would just be a stone filter. How would I verify I'm getting fuel to my pump? Just by cranking the engine?
    First I would check and see if the filter is still in place next to the tank. If so, I would replace it with a new one, they are cheap insurance and extra filtering of the fuel is not a bad thing.

    To check for fuel at the pump you can remove the outlet line from the mechanical pump and crank the engine over a time or two. I recommend disconnecting the coil wire so the car won't start. Check for fuel. If the fuel pump is working and you are pumping fuel then you need to verify that its making it to the carburetor. If you don't show the pump pumping fuel then you need to verify that you have fuel coming into the pump and also that the pump is functional and is actually pumping the fuel to the carburetor.

    This whole purpose here is process of elimination. Remove all the variables so you can verify what is actually going on and why you have a no start problem. Some of it seems silly and redundant, but I will tell you from experience there is nothing worse than throw parts at a car to fix it and ultimately determine that the issue was a simple clogged filter, fuel line, bad pump, etc. and NOT all the other things that you GUESSED might be the issue.
    ​Trey

    "I Don't build it hoping for your approval! I built it because it meets mine!"

    "I've spent most of my money on Mustangs, racing, and women... the rest I just wasted."

    Mustangs Past: Too many to remember!
    Current Mustangs:
    1969 Mach 1
    1979 Pace Car now 5.0/5 speed
    1982 GT Stalled RestoModification
    1984 SVO Still Waiting Restoration
    1986 GT Under going Wide Body Conversion Currently

    Current Capris:
    1981 Capri Roller
    1981 Capri Black Magic Roller Basket Case
    1982 Capri RS 5.0/4spd T-top Full Restoration Stalled in TX
    1984 Capri RS T-top Roller
    1983-84 Gloy Racing Trans Am/IMSA Body Parts

  9. #9
    FEP Super Member mmb617's Avatar
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    Quote Originally Posted by alexpp361 View Post
    The fuel lines themselves are tight, the mechanical fuel pump was installed correctly, but when the I try to put gas in the carburetor by pumping the throttle when the car is off no gas get's to the carb.
    So I'm reading this to mean there is no gas getting to the carb for some reason. I think that pretty much says the no start is due to no fuel, so I wouldn't worry about checking for spark or timing at this point.

    Quote Originally Posted by wraithracing View Post
    Have you verified that you are getting fuel to the fuel pump? Is the fuel pump pumping fuel up the the carburetor?
    Exactly. If gas isn't getting to the carb it's either not getting to the fuel pump or the fuel pump isn't working to push it to the carb.

    I'd pull the line from the fuel pump to the carb and have someone crank the car just for a second. If you get gas squirting out then the problem has to be at the carb. If you don't get gas there then remove the line going into the fuel pump from the gas tank. If no gas runs out when you do this then there is an obstruction somewhere either in the line from tank to pump or in the tank itself.

    Quote Originally Posted by brian.aughe View Post
    The modern gas is brutal for them and he said it's even worse for an aftermarket pump. I'm sure other guys have had different results but for me as a car that sits for lengths of time it's the worst case scenario. His advise was to electric pump it and forget it.
    I don't agree with this advice. I can't think of a reason why an electric fuel pump is better than a mechanical one on a carbbed NA car. I've run a mechanical pump on my car for the last 8 years and it often sits for long periods. The only problem I have is that it does have to crank a while longer after a long storage period but I think that's because I have much larger than stock fuel lines and it takes a while to fill them before the pump can push the gas to the carb. It always starts though.

    No starts are always frustrating but you're already ahead of the game as you know it's a fuel issue. Be methodical in your trouble shooting and you'll find the problem.
    408/T5/3.73's

    We're not fast racers, we're more what's known as half fast racers.

  10. #10
    FEP Super Member mmb617's Avatar
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    Trey beat me to the punch by 2 minutes. It goes to show that great minds think alike as he said pretty much the same things.
    408/T5/3.73's

    We're not fast racers, we're more what's known as half fast racers.

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