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  1. #1

    Default 1986 Mustang ignition issue??

    I have an '86 5.0/5 speed car and I've been having an intermittent problem with it (my favorite kind of problem...). I am in need of changing the throttle position sensor, but I don't believe this is a related problem. Occasionally the tach wigs out and starts erratically reading 1000-5000 rpm more than the motor is actually running. While it's doing this the car stumbles and makes no power. Usually as quickly as it starts doing this it goes away, but it's left me sit before. If my life depended on me guessing I'd say it's an ignition module problem? What are you guys' thoughts?

    Thanks!
    Last edited by GliDeThuNDeR; 05-27-2018 at 02:07 AM.
    Daily Driver:
    1986 Mustang GT Convertible 5.0/5spd (T5Z, VM-1, "Lightweight" tailpipes)
    Winter Car:
    1986 Mustang GT Convertible 5.0/5spd (T5Z, VM-1, "Lightweight" tailpipes)
    Show Car:
    1986 Mustang GT Convertible 5.0/5spd (T5Z, VM-1, "Lightweight" tailpipes)

    Either I use one car for everything, or I have 3 identical twins?

  2. #2

    Default

    The car has been given a coil, 2 modules, wires, and a distributor in the last 1000 miles or so. Going to try to track down a motorcraft module and see what I can make happen after work. Maybe eventually if I throw enough $ at the problem it will go away.
    Daily Driver:
    1986 Mustang GT Convertible 5.0/5spd (T5Z, VM-1, "Lightweight" tailpipes)
    Winter Car:
    1986 Mustang GT Convertible 5.0/5spd (T5Z, VM-1, "Lightweight" tailpipes)
    Show Car:
    1986 Mustang GT Convertible 5.0/5spd (T5Z, VM-1, "Lightweight" tailpipes)

    Either I use one car for everything, or I have 3 identical twins?

  3. #3

    Default

    Did the modules fix the problem when you put them on?

  4. #4

    Default

    Threw a new module in. Problem seems to have gone away. Hopefully my car doesnt think modules are a consumable.
    Daily Driver:
    1986 Mustang GT Convertible 5.0/5spd (T5Z, VM-1, "Lightweight" tailpipes)
    Winter Car:
    1986 Mustang GT Convertible 5.0/5spd (T5Z, VM-1, "Lightweight" tailpipes)
    Show Car:
    1986 Mustang GT Convertible 5.0/5spd (T5Z, VM-1, "Lightweight" tailpipes)

    Either I use one car for everything, or I have 3 identical twins?

  5. #5

    Default

    Quote Originally Posted by GliDeThuNDeR View Post
    Threw a new module in. Problem seems to have gone away. Hopefully my car doesnt think modules are a consumable.


    I would double check your body and engine to body grounds,you may have a problem there causing the boxes to eat themselves

  6. #6
    FEP Member
    Join Date
    Dec 2016
    Location
    Grand Rapids, MI
    Posts
    283

    Default

    I had a somewhat similar issue on my wagon, but it would only act up after 2+ hours of driving which made it difficult to troubleshoot. I wound up replacing the distributor, ICM, and coil with Motorcraft parts. I also remote mounted my ICM onto the driver's fenderwell to get it away from the heat of the distributor. No issues yet, but I've only been driving it around town so far. From doing some research none of the cheap (or expensive ones for that matter) aftermarket ICM's have a good reputation.
    '89 XR-7 5 Speed
    '95 SC 5 Speed
    '91 Crown Vic P72 351W
    '95 Saturn SW2
    '85 Ford LTD Squire

  7. #7
    FEP Power Member Ourobos's Avatar
    Join Date
    Apr 2008
    Location
    Waikoloa , Hawaii
    Posts
    1,863

    Default

    Had a similar issue on my 86, except RPM would dip to 200-300 then back up randomly. Tried to TFI modules, but not Motorcraft. Help briefly. Issue returned. Used a motorcraft TFI, problem solved.
    1986 CHP SSP Coupe

  8. #8

    Default

    It's interesting that you mention a grounding issue. I had an issue that was two fold a little over a year ago. The engine to body ground was bad, and the ECU ground was bad. The result was a vehicle that would blow the fuse (originally a fuse-able link) for the ECU and leave the car sit every 2-40 miles. We grounded the ECU straight to the battery and redid some of the other grounds. May need to revisit this if these issues continue. Hopefully now that I have a Motorcraft module, it'll be cured, like in Ourobos' case. Gotta love 30 year old wiring problems
    Daily Driver:
    1986 Mustang GT Convertible 5.0/5spd (T5Z, VM-1, "Lightweight" tailpipes)
    Winter Car:
    1986 Mustang GT Convertible 5.0/5spd (T5Z, VM-1, "Lightweight" tailpipes)
    Show Car:
    1986 Mustang GT Convertible 5.0/5spd (T5Z, VM-1, "Lightweight" tailpipes)

    Either I use one car for everything, or I have 3 identical twins?

  9. #9

    Default

    My radiator isn't in the best shape, and my motor is running a little on the hot side as a result. I wonder if this is a contributing factor? (Going to get temps under control either way, just interesting to consider)
    Daily Driver:
    1986 Mustang GT Convertible 5.0/5spd (T5Z, VM-1, "Lightweight" tailpipes)
    Winter Car:
    1986 Mustang GT Convertible 5.0/5spd (T5Z, VM-1, "Lightweight" tailpipes)
    Show Car:
    1986 Mustang GT Convertible 5.0/5spd (T5Z, VM-1, "Lightweight" tailpipes)

    Either I use one car for everything, or I have 3 identical twins?

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