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  1. #26

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    I would seriously try grounding the hell out of it first. I just replaced my map ect the air charge temp thingy, etc and I still got codes (all motorcraft). I ran a ground wire from the firewall to a stud on the CFI, removed the plumbers tape from the ECT (my bad), and now all is good. 11 10 11 (KOEO) makes me so happy.

    I am still chasing a grounding issue (i think) on my temp and oil pressure guage and fuel gauge (occasionally they both move up a about a letter in tandem, then drop back). So I also ran a ground wire to the alternator bracket from the battery and another from the firewall to the ignition coil.
    1984.5 G.T.350 5.0 CFI AOD Convertible (TRX package, loaded)
    Hooker Super Comp Shorty Equal Length Headers
    GT40 heads, Edelbrock 3721, K&N filter in stock dual snorkel,
    Comp cams XE254H, hypereutectic pistons, catted BBK H-pipe, full custom duals.
    3.73 rear. CS5 225/60/15 on 10 holes (street) Federal 595 rs-rr 225/45/15 on 10 holes (race)
    Everything else stock and fully functional.

  2. #27

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    Ground strap from motor to body go to hell over time.

    Add a ground cable from the ground lead attachment point on the motor to the K member or the frame of the car

    The ECU ground lead bundle that condensed to one wire is crap. ditch this ground lead where it attaches to the drivers fender remove it. Follow it down to the four wire bundle and cut it off.

    Get a nice loop that fits over your negative terminal bolt along with a nut and a nice heavy wire. Crimp on the loop then solder it for good measure. Sandwich the loop between your existing negative lead nut and the new one and torque it down snug. Cross Wrap the other end of the wire and the four wire bundle securely. Use copper wire like you would use a bread tie. Now solder this wires in this bundle and wrap them up with insulation when done

    that will eliminate some common causes of ground issues

  3. #28
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    Definitely want to check out the grounds. That will give us something to do this weekend.


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  4. #29

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    Don’t just look at them.

    The ones on my son’s 86 look fine but are faulty. I stated what we did to fix them.

    We spent weeks chasing gremlins and another forum member came and helped us find the problems using a current flow measurement loop.

  5. #30

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    Do a resistive check ohm everything out and read the continuity between the block or the battery and whatever sensor wire you suspect to be broken almost everything there uses the 5-volt reference if you have a bad ground your sensors will actually read higher than 5 volts because of the high resistance in the circuit
    2 1986 cougars (both 4 eyed and 5.0)
    1 1987 cougar

  6. #31

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    I would also check and clean the main ground my buddy bought a car that just randomly died hold codes got pretty much the exact same codes you got everything was broken and didn't work right and we ended up troubleshooting it down to the ground wire on a 5l EFI motor it grounds right next to the battery and there's a small plastic connector and that plastic connector was damaged by somebody carelessly throwing the battery in and pulling the wire out
    2 1986 cougars (both 4 eyed and 5.0)
    1 1987 cougar

  7. #32
    FEP Power Member Ray Dog's Avatar
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    My thoughts are to change the cheapest or easiest item to change, and not do all of them at one time.
    My experience working with industitrial machinery electronic controls with diagnostic displays, mulitple errors at the same
    time are usualy a cause of lost or faulty voltage supplies.
    By doing one item and clearing the fault will confirm bad item and not a voltage loss.
    Another thought is check the integraty of all connections.
    A corroded conector or wire will cause low volts as well. Think of it as a exrta resistor added to the circuit.
    Ray
    95 Saturn SL2 (Kid's Ride)
    08 Magnum (The Roadie Wagon)
    84 Capri 4 cyl 4 speed (DD).............................................. Used to own
    86 Mustang LX 3.8 Convertible (bought new)......................Too many
    00 E-150 Sherrod conversion van (The Silver Land Whale)...notables
    94 Saturn SL2 (my wife's car, bought new, before me)........65 Chevelle SS, 69 Torino GT, 39 Willys Overland, 69 Fleetwood
    65 Galaxie 500 XL 390 auto (on deck waiting for funds).........81 Mustang T-Roof hatch, 88 Lincoln LSC, 86 Saab 900

  8. #33

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    Cleaned up the grounds last weekend and adjusted timing. Runs a bit better but still having our issue. I'll be buying a new TPS, MAP, and EVP this weekend and see if that clears up anything since those were the codes thrown at us. Very excited to see progress with this engine.


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  9. #34
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    Opened up the ECU to have a look inside. Definitely a problem here.


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  10. #35

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    That sucks but itís easy enough to fix. Just solder in a heavy jumper wire to take the place of the board trace. Take your time. Use Rossin core solder

    Check your capacitors also

    you may want to consider asking the Mcparts store to locate another ECU for you.

    I tend to hord them while while I can still get them. I have one extra that is compatible for each of my 86GT EFI cars.

    Certain tunes are way better than others on the V8 cars. Not sure on the V6ís but Iíd assume itís more of the same.

    Back in college on a bet I once desoldered a working AMD 386DX40 from a broken motherboard and soldered it into a nicer board with a trashed CPU and got it up and working again ..... not for the faint at heart. This one wonít be too bad. Practice on something you donít care about first!

    oh ó and good luck! I hope this is the cause and not the effect and fixes your car!
    Last edited by erratic50; 08-01-2018 at 10:48 PM.

  11. #36
    FEP Power Member Ray Dog's Avatar
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    Erratic50 makes a good point, the trace looks like it was burned out from too much current.
    The senser or load could be shorted or the wiring is bad.
    Been there, fixed that.
    Ray
    95 Saturn SL2 (Kid's Ride)
    08 Magnum (The Roadie Wagon)
    84 Capri 4 cyl 4 speed (DD).............................................. Used to own
    86 Mustang LX 3.8 Convertible (bought new)......................Too many
    00 E-150 Sherrod conversion van (The Silver Land Whale)...notables
    94 Saturn SL2 (my wife's car, bought new, before me)........65 Chevelle SS, 69 Torino GT, 39 Willys Overland, 69 Fleetwood
    65 Galaxie 500 XL 390 auto (on deck waiting for funds).........81 Mustang T-Roof hatch, 88 Lincoln LSC, 86 Saab 900

  12. #37

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    You should be able to ohm that out vs the lead it maps to and the ground hopefully! Sure hope you get this nailed down soon!

  13. #38

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    If you're lazy you could sneak in a fuzable link at that point. Ugly but if the problem was transient or fixed by your troubleshooting...
    1984.5 G.T.350 5.0 CFI AOD Convertible (TRX package, loaded)
    Hooker Super Comp Shorty Equal Length Headers
    GT40 heads, Edelbrock 3721, K&N filter in stock dual snorkel,
    Comp cams XE254H, hypereutectic pistons, catted BBK H-pipe, full custom duals.
    3.73 rear. CS5 225/60/15 on 10 holes (street) Federal 595 rs-rr 225/45/15 on 10 holes (race)
    Everything else stock and fully functional.

  14. #39
    FEP Member
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    I tried soldering in a jumper, but I lack both the skills and patience to do it. Iíve got a couple friends that may be able to do it for me. Also have a line on a used ECU.


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  15. #40

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    well. got the ECU fixed and she's running fine now.


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  16. #41

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    That is great! What a crazy pain in the bum. Is it still throwing codes?
    Last edited by emerygt350; 08-04-2018 at 06:27 PM.
    1984.5 G.T.350 5.0 CFI AOD Convertible (TRX package, loaded)
    Hooker Super Comp Shorty Equal Length Headers
    GT40 heads, Edelbrock 3721, K&N filter in stock dual snorkel,
    Comp cams XE254H, hypereutectic pistons, catted BBK H-pipe, full custom duals.
    3.73 rear. CS5 225/60/15 on 10 holes (street) Federal 595 rs-rr 225/45/15 on 10 holes (race)
    Everything else stock and fully functional.

  17. #42

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    haven't checked. just need to adjust timing and get the front end sorted out


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  18. #43

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    Glad it’s fixed!

  19. #44

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    just ran through codes today. nothing came back. still had to ground out the harness but i'm relieved that this car is running right. I'd like to thank everyone involved with figuring this issue out.


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  20. #45

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    Nice.
    1984.5 G.T.350 5.0 CFI AOD Convertible (TRX package, loaded)
    Hooker Super Comp Shorty Equal Length Headers
    GT40 heads, Edelbrock 3721, K&N filter in stock dual snorkel,
    Comp cams XE254H, hypereutectic pistons, catted BBK H-pipe, full custom duals.
    3.73 rear. CS5 225/60/15 on 10 holes (street) Federal 595 rs-rr 225/45/15 on 10 holes (race)
    Everything else stock and fully functional.

  21. #46

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    Sucks that it was the ecu, but good on ya for not just getting confused and giving up. Too many people get rid of the car over stuff like that.
    2 1986 cougars (both 4 eyed and 5.0)
    1 1987 cougar

  22. #47

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    Quote Originally Posted by Haystack View Post
    Sucks that it was the ecu, but good on ya for not just getting confused and giving up. Too many people get rid of the car over stuff like that.
    Thankfully we didn't have to buy a whole new ecu, free and easy fix.


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  23. #48

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    Personally I’d look for another compatible ECU and keep it around. They aren’t getting easier to find!

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