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  1. #1

    Default need help/advise on bad running 5.0

    I have a 1986 Capri 5.0 that I have been restoring. recently it has developed a miss in the engine and it is not just a single cylinder (checked headers with temp gun and pipes are all about the same). When you rev the engine (WOT) up it falls on its face and sputters until you let off the gas and then it idles fine. If you WOT it will just sputter until you let off the throttle ( could sputter for several minutes if you hold down the pedal WOT). I also noticed that all the plugs are black (way to much fuel). I have replaced the plugs, Brand new wires, TPS., Ign. module on dist.. I have noticed that when I do the volt test on the TPS the reading don't seem to change when I open the butterfly and I have put 3 different TPS sensors on it. Checked the ground on the engine harness too. The engine is all stock except a set of headers. Thank you for any input.
    1986 ACS McLaren Capri
    1982 Mustang GT

  2. #2
    FEP Senior Member qikgts's Avatar
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    Two things I would look at.

    1- Troubleshoot the 5v circuit which feeds the TPS (and other sensors) and verify all is good. Until you have a TPS that shows changing voltage anything else is futile.

    2- If fixing the TPS hasn't solved the black plugs, take a look at the fuel regulator on the rail and verify the vacuum line is all good and the regulator itself is functioning correctly.
    '85 GT

    The other one... 2016 F-150 XLT Supercab Ecoboosted with 3.73's...

  3. #3
    FEP Member Tigger's Avatar
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    I would also check for engine codes.
    67 Mustang Coupe
    96 Tangerine GT
    86 Saleen #179

  4. #4
    FEP Senior Member qikgts's Avatar
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    Quote Originally Posted by Tigger View Post
    I would also check for engine codes.
    Absolutely a wise suggestion!
    '85 GT

    The other one... 2016 F-150 XLT Supercab Ecoboosted with 3.73's...

  5. #5

    Default

    I'd look at the ignition coil too.

  6. #6

    Default

    I found a lot of good info from these sites
    http://www.veryuseful.com/mustang/te...ng-ECC-EFI.gif
    and the second post here
    https://www.stangnet.com/mustang-for...p-coil.784994/
    1978 Mercury Zephyr boxtop 5.0 EFI T5Z 8.8
    1999 Ford Contour 2.5 V6 5 speed
    2016 Ford Focus ST 2.0 Ecoboost 6 speed

  7. #7
    FEP Supporter Broncojunkie's Avatar
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    If your plugs look that bad, I can guarantee your O2 sensors are going to look bad, too. Probably cat converters dirty, as well.
    Is the engine completely stock? Maf conversion? Stock injectors? Have you checked fuel pressure regulator? All things I would look at.

  8. #8
    FEP Supporter Broncojunkie's Avatar
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    Another thing I forgot, what temp does it run? Does the engine temp stay well below the halfway mark?

  9. #9

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    That sounds like what I went through on my 86. I replaced EVERYTHING I could think of and it turned out to be the distributor pickups were bad. That was on a rebuilt distributor! I replaced it and... runs like a champ, now.

    It could have been any of the sensors, plugs, wires, etc that I replaced in concert with the distributor, but that's how I finally figured it out.

  10. #10
    FEP Member
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    Is the 5 volt reference voltage reading 5 volts? That's what you should see going into the TPS. If you see battery voltage, you have a bad CPU ground.

  11. #11

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    TPS is critical..... fix that

    also verify you are seeing advance at the distributor when you try to rev it. Use a timing light and watch the marks as you try to rev it up.

    verify your coil wire isnít fried. Also that the rotor are good. Not new, good. Inspectcthe cap for signs of how the spark distribution is under the cap. I had one distributor wear out after around 430K miles and the shaft let the rotor go all over the place

    Make sure the advance spout and wiring is good. Iíve had one where it made connection but couldnít carry enough current to actually advance the distributor on my 460. Talk about a truck that ran like crap!! Itís totally awesome now.....
    Last edited by erratic50; 12-08-2018 at 08:32 PM.

  12. #12

    Default

    Quote Originally Posted by Tigger View Post
    I would also check for engine codes.
    This°
    2 1986 cougars (both 4 eyed and 5.0)
    1 1987 cougar

  13. #13

    Default

    The coolant temp sensor on the steel rail is mission-critical to these old systems. That's what triggers, partially, cold weather enrichment. If that sensor is sending faulty readings the computer may think it's fourty below and drown the engine in fuel. The air charge temp sensor can also cause this reaction from the EEC.

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