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  1. #1

    Default 1986 Shut Off/FUel Pump Issues

    Hey what's up guys, Im new to the forum here.

    So here's my dilemma. I have a 1986 GT 5.0 That keeps shutting off. You start the car up, it runs fine, sometimes for a few minutes, sometimes for a few seconds. Sometimes it will shut off on its own, sometimes it will happen if you press the throttle. RPMs will drop and the engine will shut off, just as if you had pulled the key out. Whats weird though is AFTER it does this every time, I hear the fuel pump prime/ go through its cycle- it makes the whining noise.

    THEN if i try to start the car back up, I have to pull the key out, re-prime the fuel pump, and then it will start. If I dont, it will just crank and not fire up. I have 40psi fuel pressure, so it's definitely getting fuel to the engine, why it dies just confuses me though.

    ALSO this is another goofy thing.. If there's no key in the ignition, and i turn the parking lights on, this will cause the fuel pump to prime. WITH THE PARKING LIGHTS. Then the fuel pump usually floods the engine after this.. So the fuel pumps gotta be shorting on something right? Or maybe i have a loose/bad ground somewhere? This whole thing confuses me, so any help/advice is appreciated... Just wanna hear if anyones had the same/similar issue..

    it has new:
    battery/ ground cables
    spark plugs /wires
    cap and rotor
    coil pack
    tfi module
    throttle body
    IAC Valve
    Throttle position sensor
    o2 Sensors

    The problem started before this stuff was replaced though.


    Thanks in advance -Trent

  2. #2
    FEP Super Member erratic50's Avatar
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    First guess is ignition switch. Look to see if it is separating on you.





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  3. #3

    Default

    Gotcha. You mean like make sure the wire isnt broken or rubbing on anything?

  4. #4

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    The switch itself often fails with age. The entire load of all the electrics for the whole car run through it. As it ages, it gets charred up and is honestly way undersized for the types of load it sees. One bad contact and the whole thing can melt and burn the car to the ground.

    Take off the steering colum lower cover. Behind the ignition key is a little box with about 20 wires going into it. This is the ignition switch we are refering to. Its held on by two bolts. Sometimes security torx bits, sometimes a small 3/8 or so sized headed bolt, sometimes a special fastener where the head shears off to "prevent" theft. Get a small pair of vice grips and take your time or get a dremel and slot the bolts until you get then out.

    A new switch will cost about $20. There is a chance the plug is also melted. Good luck and let us kniw whst you find.
    2 1986 cougars (both 4 eyed and 5.0)
    1 1987 cougar

  5. #5
    FEP Super Member erratic50's Avatar
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    The other thing is sometimes the crappy connectors Ford used on the end of the wires go bad. Look carefully to make sure there is no clear evidence of heat or arcing on each blade of the connector. I've had some go bad over the years. Solder, shrink tubes, and new contacts inside the connector to the rescue.

    99.9% of the time it's just a bad switch. I replace mine every time there is even a hint of trouble. If you can find them, the last release from ford is a better switch. If you can't, the Mcparts store switches are often quite good for 50-100K miles

    Good luck!

  6. #6

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    Yeah I pulled the switch out and it doesnt look burned or melted, but the contacts are very dirty. I'll replace the whole switch/connector and see if that helps.

  7. #7

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    So I replaced the ignition switch and it didnt fix it.. I WILL SAY it did run for like a solid 5-8 minutes which it hasnt done in a while... But it still died and after that it would only run for like a minute at a time. I did definitely notice I could hear the fuel pump lightly making its whining time the whole time the car was running.. Then it would sound like it would get a little louder, and the car would shut off, and the fuel pump would whine on for a few more seconds.. And it sounded very rough when it would do it..

  8. #8

    Default

    It sounds like the EEC and fuel pump relay combo isn't working like they are designed to, but with the physical running and quitting, the fuel filter might be clogged. It doesn't take much - any resistance sensed to blowing through it, and it's time for a new one. Hearing the fuel pump running while the car is running is normal, but then getting louder indicates it's progressively trying to operate under harder and harder conditions, higher pressures/restriction, like a clogged past-due-to-change fuel filter, or a kinked fuel line etc...
    Mike
    1986 Mustang convertible ---> BUILD THREAD
    Past Fox-chassis "four eyes":
    1983 Mercury Cougar LS
    1986 Ford Thunderbird ELAN
    1980 Capri RS Turbo

    Work in progress website ---> http://carb-rebuilds-plus.boards.net/

  9. #9

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    I actually replaced the fuel filter not long ago.. I put some fuel treatment cleaner in the tank awhile ago so maybe it broke some debris loose and it got stuck in the lines? But them again Im still getting fuel pressure up front

  10. #10

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    Last I owned an EFI vehicle, an '86 5.0L Elan Thunderbird, the addition of fuel injector/system cleaner caused 4 more filters to get clogged before it smartened up and ran right.
    Mike
    1986 Mustang convertible ---> BUILD THREAD
    Past Fox-chassis "four eyes":
    1983 Mercury Cougar LS
    1986 Ford Thunderbird ELAN
    1980 Capri RS Turbo

    Work in progress website ---> http://carb-rebuilds-plus.boards.net/

  11. #11

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    Oh oh great! Good to know though. Just hoping I didnt do any other damaged with that stuff

  12. #12

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    I had my fuel pump die. Both times it died on me it was on the job or with my kids on a 95+º day. I checked fuel pressure at the filter and got 60 psi when it was cold. every day it wasnt 90+ the car was fine.

    Wednesday was my dad off, ran codes, nothing came up. Decided to drive it until it died again. After 5 hours of 95+º weather i gave up. Then it of course died, was pushing 40psi for about 30 seconds then if would drop down slowly to about 20 psi. Longer if ran, the lower it went.
    2 1986 cougars (both 4 eyed and 5.0)
    1 1987 cougar

  13. #13

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    The tail lights and fuel pump relay are in the same harness that runs from the hatch area. The relay is the green box under the drivers side seat and also mixed in that harness is the drivers side seat belt plug. Maybe there's a short somewhere ?

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