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  1. #1

    Default Fuel pump still not priming

    Ok guys I need some help:
    New gas tank, fuel pump, filter, sending unit and relay under the driver seat.

    What am I missing that I need to replace or check?

    Thanks!
    FOLLOW MY RESTORATION ON INSTAGRAM @302_much

    1986 Mustang GT Hatchback
    Tan interior, 151,000 miles, acquired in March 1988, cold air intake, Bondurant Racing H pipe with built in bullet mufflers where cats should be, MAC shorty headers, pro 5.0 shifter, slotted front rotors, cobra wheels, chrome strut tower, white face gauges and more to come. Complete restoration in progress started September 2020.

  2. #2

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    More gas?

    Do you hear the pump whine for ~5-10 seconds when you turn the key?
    The pump will shutoff after 5-10 seconds of the engine doesn't start.

    So, try multiple "turn key on, wait 5 secs", "turn key off, wait 30 secs" cycles.

    Otherwise, you may have a loose hose?

    Did you replace the sock in at the end of the pump? Did you get the Pump back into it's correct PITA place and location? There's a baffle in the tank. Once you figure the correct way to insert the pump, then "it's easy". Otherwise, it's a good reason to try new swear words.

    Good Luck!

  3. #3

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    Thanks, there is no normal whine for the pump priming and thus that lead to all the new parts. After owning a fox body for so many years you immediately notice when the fuel pump does not prime. It is installed correctly with sock and I did try 3 or 4 times turning the key. I think there are a few other relays or things to check that are keeping the pump from getting power.
    FOLLOW MY RESTORATION ON INSTAGRAM @302_much

    1986 Mustang GT Hatchback
    Tan interior, 151,000 miles, acquired in March 1988, cold air intake, Bondurant Racing H pipe with built in bullet mufflers where cats should be, MAC shorty headers, pro 5.0 shifter, slotted front rotors, cobra wheels, chrome strut tower, white face gauges and more to come. Complete restoration in progress started September 2020.

  4. #4
    FEP Power Member Jerry peachuer's Avatar
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    Do you know if it has the inertia switch and if so is it in need of resetting?

    If car rolls over or rear ended or whichever it trips the power to the pump

  5. #5

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    The schematic for the fuel pump is simple:

    See:
    http://www.veryuseful.com/mustang/te...ng-ECC-EFI.gif





    Start with the fuel pump relay.
    Make sure you have power at the yellow wire.

    Check the Inertia switch.
    Check the Red power in, and the Red/Black power out.

    When you first turn the key, the tan/light-green wire on the fuel pump relay should go to ground

    When you first turn the key, check the Pink/Black wire from the fuel pump relay.


    Good Luck!

  6. #6

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    I bypassed the inertia switch last night with no luck. I am going to have to get a meter and start at the rear and start with the connection at the gas tank and then move to the inertia switch and then the relay. If nothing at the relay my understanding is part of that power comes directly from the ECU and I would assume if that is the case that I would need to replace that.

    I do believe the inertia switch is bad based on the fact that the white reset just sits flat and you cannot push it to reset it. I am going to replace it anyway but once I run the meter on it hopefully it will tell me where the power is ending.

    Thanks for all the info and I will update later this week when I have time to test it all out.
    FOLLOW MY RESTORATION ON INSTAGRAM @302_much

    1986 Mustang GT Hatchback
    Tan interior, 151,000 miles, acquired in March 1988, cold air intake, Bondurant Racing H pipe with built in bullet mufflers where cats should be, MAC shorty headers, pro 5.0 shifter, slotted front rotors, cobra wheels, chrome strut tower, white face gauges and more to come. Complete restoration in progress started September 2020.

  7. #7
    FEP Power Member 87gtVIC's Avatar
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    The inertia switch POPs when smacked. You push it down to restore connection. You can smack it with a deadblow and see if it pops up.

  8. #8
    FEP Power Member Jerry peachuer's Avatar
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    There is a relay under the dash that you should look at soon as a possible reason

  9. #9

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    Quote Originally Posted by Jerry peachuer View Post
    There is a relay under the dash that you should look at soon as a possible reason
    ???
    Not for the fuel pump in a 1986.
    And, it's not shown in the schematic.


    The fuel pump relay for an '86 mustang is under the front driver's seat.

    Picture below from:
    https://lmr.com/products/fox-body-mu...elay-locations


  10. #10
    FEP Power Member Jerry peachuer's Avatar
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    Not sure on years but my buddies 88 had one on lower kick panel passenger side

    I believe there is 2 plus inertia switch

  11. #11
    FEP Power Member Jerry peachuer's Avatar
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    I'm 100 percent positive there's a relay in the kick panel hidden up high on factory 88gt speed density setup

    Previous owner had pump on toggle and this was fixed by changing out this relay.. alot of work and some back yard questionable hack job to run toggle vs changing out this relay

    Now this may not be necessarily a fuel pump relay but maybe it gives a ground or power to that circuit which is where you may be now.. e
    Its a very easy 10 minute check its up tucked out of the way and not in plain sight but accessible

    Good luck hopefully I don't throw you off on your search

  12. #12

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    Oh, that sounds like maybe the EEC Power Relay?
    Yup, that also needs to be working.
    Good catch! :-)


    https://mustangforums.com/forum/5-0l...tall-pics.html

    https://i1177.photobucket.com/albums...stockmount.jpg

  13. #13

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    Quote Originally Posted by stangPlus2Birds View Post
    The schematic for the fuel pump is simple:

    See:
    http://www.veryuseful.com/mustang/te...ng-ECC-EFI.gif





    Start with the fuel pump relay.
    Make sure you have power at the yellow wire.

    Check the Inertia switch.
    Check the Red power in, and the Red/Black power out.

    When you first turn the key, the tan/light-green wire on the fuel pump relay should go to ground

    When you first turn the key, check the Pink/Black wire from the fuel pump relay.


    Good Luck!
    Ok, so I am not that great with electrical but I did borrow a meter and get it set up of Ohm testing. Last night I was able to test the Inertia switch by doing the following. Red into red and black into red/black. When turning the key to the on position with clutch engaged I got a 38-40 reading.

    I assume this means that there is power going to the inertia switch but have not idea what it should read.

    If I had power there, how do i check the pigtail/connector the plugs into the fuel pump harness. Is it possible I am not getting power from the Inertia switch somehow? I did hit the inertia switch and it popped up so it does work and I was able to reset it.

    Any additional help is appreciated as I am out of my comfort zone at this point.

    Thanks,

    Shawn
    FOLLOW MY RESTORATION ON INSTAGRAM @302_much

    1986 Mustang GT Hatchback
    Tan interior, 151,000 miles, acquired in March 1988, cold air intake, Bondurant Racing H pipe with built in bullet mufflers where cats should be, MAC shorty headers, pro 5.0 shifter, slotted front rotors, cobra wheels, chrome strut tower, white face gauges and more to come. Complete restoration in progress started September 2020.

  14. #14

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    Quote Originally Posted by Jerry peachuer View Post
    I'm 100 percent positive there's a relay in the kick panel hidden up high on factory 88gt speed density setup

    Previous owner had pump on toggle and this was fixed by changing out this relay.. alot of work and some back yard questionable hack job to run toggle vs changing out this relay

    Now this may not be necessarily a fuel pump relay but maybe it gives a ground or power to that circuit which is where you may be now.. e
    Its a very easy 10 minute check its up tucked out of the way and not in plain sight but accessible

    Good luck hopefully I don't throw you off on your search
    Happy to check that too and I had seen different info on whether that was something to check in an 86. It does appear I am getting power to the inertia switch so unless that has something to do with the connector afterwards I may not have to fool with it.

    Appreciate all responses as I try to get this thing running again!
    FOLLOW MY RESTORATION ON INSTAGRAM @302_much

    1986 Mustang GT Hatchback
    Tan interior, 151,000 miles, acquired in March 1988, cold air intake, Bondurant Racing H pipe with built in bullet mufflers where cats should be, MAC shorty headers, pro 5.0 shifter, slotted front rotors, cobra wheels, chrome strut tower, white face gauges and more to come. Complete restoration in progress started September 2020.

  15. #15
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    Set your meter for voltage when testing a live circuit. Use the ohms setting only on circuits that are not connected to power. Use the amps setting when inserting the meter leads between components of a circuit, for example, between a bulb and its socket. Never use the amps setting between battery leads and ground, unless you want large arcs, blown fuses, and a smoking pile of junk that used to be a meter.

  16. #16

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    You could have a bad ECU. I have an X3Z that will not turn the pump on. It needs a refurb

    No need to reply but here’s what experience has taught me

    Is the ECU relay getting power?

    We had a regular old cluster F on my sons 86. We isolated it to the fusible link for the ECU relay but we kept cooking them repeatedly.

    What it actually was root cause was a combination of a lot of neglect and some bad wiring practices by the previous owner. The stiffening cap for the stereo was ran with a ground to the body but they never made sure the body had a good ground.

    The engine to body grounding strap was bad

    The ECU ground bundle wasn’t making a good connection because of corrosion inside the connector that connects the ground bundle to the drivers front fender

    The body to ECU ground strap was gone

    The seal for the radio antenna had failed and water was running in

    The ECU relay was hanging instead of being mounted and the relay had filled with water

    The fix was easy enough.....

    New sealed fuse holder to replace the fusible link
    New ECU relay to replace the one full of water
    New ground lead from engine ground connection to the K member
    New ground lead body to ECU at the ECU

    And lastly and most importantly .....
    New ground lead from battery to ECU ground bundle removing fender connection. We put a ring connector over the negative terminal bolt and added a second nut. We ran that back to the 4 wire ECU bundle where we soldered and shrink tubed everything

    No more problems since — knock on wood

  17. #17

    Default

    Ok I am learning as I go along so see if these questions and understanding make sense.

    1. If the relay under the seat clicks then it should be sending power only to the inertia switch since there is only one wire leading to that and that would mean everything was working to that point
    2. There is only a power wire leading from the inertia switch to the plug where the harness for the fuel pump is plugged in. That same harness gets its ground from the ECU? If so, I assume the red/black wire is still the power coming from the inertia switch but which wire is the ground going to that plug. There are 4 wires I believe and 2 of them are black, one red/black and I don't remember the other color.
    3. If I run a voltage test at that plug and there is not reading then that would possible mean i need to replace the ECU

    Is this logic correct? Am I missing something else?

    Thanks again for everyone's patience....again this is all new territory for me.
    FOLLOW MY RESTORATION ON INSTAGRAM @302_much

    1986 Mustang GT Hatchback
    Tan interior, 151,000 miles, acquired in March 1988, cold air intake, Bondurant Racing H pipe with built in bullet mufflers where cats should be, MAC shorty headers, pro 5.0 shifter, slotted front rotors, cobra wheels, chrome strut tower, white face gauges and more to come. Complete restoration in progress started September 2020.

  18. #18
    FEP Power Member Jerry peachuer's Avatar
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    Set the schematic aside for a second and look in the kickpanel passenger side

    There is more than 1 relay in there and one of them will mess with power to the pump and its something that just stopped working per your original post

    Personally I would say your old pump is still good as well and you may find out it was just a 20.00 realay

    I believe its the WOT relay that cuts AC off when your WOT

    My buddies car had this happen and I know the schematic don't lie but there's changeover years and misprints and such so good visual

    Also there is a test port to test your fuel pump if you search how to

  19. #19

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    Quote Originally Posted by Jerry peachuer View Post
    Set the schematic aside for a second and look in the kickpanel passenger side

    There is more than 1 relay in there and one of them will mess with power to the pump and its something that just stopped working per your original post

    Personally I would say your old pump is still good as well and you may find out it was just a 20.00 realay

    I believe its the WOT relay that cuts AC off when your WOT

    My buddies car had this happen and I know the schematic don't lie but there's changeover years and misprints and such so good visual

    Also there is a test port to test your fuel pump if you search how to
    I will check that too. Fuel pump, gas tank and sending unit are brand new as is the relay under the drivers seat. Also going to check the fusible links at the solenoid as I have not checked that bunch of jumbled mess either.

    Slowly narrowing it down and appreciate the response! I think I have another relay laying around as it was probably not was bad to begin with.

    Shawn
    FOLLOW MY RESTORATION ON INSTAGRAM @302_much

    1986 Mustang GT Hatchback
    Tan interior, 151,000 miles, acquired in March 1988, cold air intake, Bondurant Racing H pipe with built in bullet mufflers where cats should be, MAC shorty headers, pro 5.0 shifter, slotted front rotors, cobra wheels, chrome strut tower, white face gauges and more to come. Complete restoration in progress started September 2020.

  20. #20

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    Quote Originally Posted by Jerry peachuer View Post
    My buddies car had this happen and I know the schematic don't lie but there's changeover years and misprints and such so good visual
    Actually, for Ford in the 70s', 80's, and 90's, the POS schematics are as useful/reliable as dress-sizes and pants-sizes. Many reasons for that.
    I have Three Ford Factory Service Schematics for my '86 T-bird. None are correct, all are different. I had bad (corroded) main power wires near the battery. I ended up having to remove the MC and booster, because the number and color or wires were different. Otherwise, I would've just run new section wires to the wire end-points.

  21. #21

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    Quote Originally Posted by smwmustang View Post
    Ok I am learning as I go along so see if these questions and understanding make sense.

    1. If the relay under the seat clicks then it should be sending power only to the inertia switch since there is only one wire leading to that and that would mean everything was working to that point
    2. There is only a power wire leading from the inertia switch to the plug where the harness for the fuel pump is plugged in. That same harness gets its ground from the ECU? If so, I assume the red/black wire is still the power coming from the inertia switch but which wire is the ground going to that plug. There are 4 wires I believe and 2 of them are black, one red/black and I don't remember the other color.
    3. If I run a voltage test at that plug and there is not reading then that would possible mean i need to replace the ECU

    Is this logic correct? Am I missing something else?

    Thanks again for everyone's patience....again this is all new territory for me.


    Don't test willy/nilly.
    Test/probe with a strategy.


    Quote Originally Posted by stangPlus2Birds View Post
    The schematic for the fuel pump is simple:

    See:
    http://www.veryuseful.com/mustang/te...ng-ECC-EFI.gif



    Start with the fuel pump relay.
    Make sure you have power at the yellow wire.

    Check the Inertia switch.
    Check the Red power in, and the Red/Black power out.

    When you first turn the key, the tan/light-green wire on the fuel pump relay should go to ground

    When you first turn the key, check the Pink/Black wire from the fuel pump relay.


    Good Luck!

  22. #22

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    @stangplus2birds...you are correct and I will run through this order!

    However, take a look at the photos I took this morning at the starter solenoid and see what I found. Now, to my knowledge I never had any electrical work done on this car other than a custom stereo and this car was running and then the fuel pump just quit working.

    These wires did not just come off on their own and may not have anything to do with it not working but there are also 2 relays right below the solenoid that I am not sure what they go to or why one of them is just uncovered and has two wires just hanging unconnected?

    I am guessing the one wire that does appear to be a ground should be connected to either the firewall or the solenoid itself.

    All comments welcome. I have not started cleaning up the engine bay yet so yes it is dirty.

    Well it will not let me upload photos so I will keep trying.

    Shawn
    FOLLOW MY RESTORATION ON INSTAGRAM @302_much

    1986 Mustang GT Hatchback
    Tan interior, 151,000 miles, acquired in March 1988, cold air intake, Bondurant Racing H pipe with built in bullet mufflers where cats should be, MAC shorty headers, pro 5.0 shifter, slotted front rotors, cobra wheels, chrome strut tower, white face gauges and more to come. Complete restoration in progress started September 2020.

  23. #23

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    System will no longer let me upload photos. If anyone has any info on this let me know. Tried to find where to email moderator but could not find that either.
    FOLLOW MY RESTORATION ON INSTAGRAM @302_much

    1986 Mustang GT Hatchback
    Tan interior, 151,000 miles, acquired in March 1988, cold air intake, Bondurant Racing H pipe with built in bullet mufflers where cats should be, MAC shorty headers, pro 5.0 shifter, slotted front rotors, cobra wheels, chrome strut tower, white face gauges and more to come. Complete restoration in progress started September 2020.

  24. #24

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    FOLLOW MY RESTORATION ON INSTAGRAM @302_much

    1986 Mustang GT Hatchback
    Tan interior, 151,000 miles, acquired in March 1988, cold air intake, Bondurant Racing H pipe with built in bullet mufflers where cats should be, MAC shorty headers, pro 5.0 shifter, slotted front rotors, cobra wheels, chrome strut tower, white face gauges and more to come. Complete restoration in progress started September 2020.

  25. #25

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    Quote Originally Posted by smwmustang View Post
    Ok, so I am not that great with electrical but I did borrow a meter and get it set up of Ohm testing. Last night I was able to test the Inertia switch by doing the following. Red into red and black into red/black. When turning the key to the on position with clutch engaged I got a 38-40 reading.

    I assume this means that there is power going to the inertia switch but have not idea what it should read.

    If I had power there, how do i check the pigtail/connector the plugs into the fuel pump harness. Is it possible I am not getting power from the Inertia switch somehow? I did hit the inertia switch and it popped up so it does work and I was able to reset it.

    Any additional help is appreciated as I am out of my comfort zone at this point.

    Thanks,

    Shawn
    Keep in mind that when testing a component or circuit for ohms,it first must be removed from power and ground in order to get a correct reading.Example: if you were testing a single wire that was connected to the EEC at one end and to the EEC relay at the other end,you would need to disconnect the wiring harness plug from the ECM & the plug from the EEC relay then touch one meter probe to the EEC end of that wire & touch the other meter probe to the EEC relay end of that wire and that would give you the right results.BTW - a reading of 5.0 ohms or less is the result you would wanna see to indicate that wire has good continuity. To test the inertia switch, disconnect the harness first then test directly across the switch terminals with the button tripped then reset. It should read OL or infinite when tripped and show a certain number of ohms when reset. You can also leave the harness attached and check the voltage coming in and going out by backprobing the harness plug.Another important note about the inertia switch is the following:
    86-90 models- the switch will kill power to the fuel pump relay.
    91-93 models- the switch will only kill power to the fuel pump itself.
    So before I go any further writing,I'll give you this awsome trouble shooting writeup titled
    "Fuel Pump Diagnosis 101". It uses a step by step process to help you pinpoint the fault.


    https://www.allfordmustangs.com/thre...230560/#/enter

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