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Thread: 1986 Cougar 3.8 L won't idle.

  1. #21
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    Derp. Yeah.

  2. #22
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    Quote Originally Posted by JeremyB View Post
    Still my first thought. No offense, but not sure your mechanics have the background to solve the problem without just throwing parts at it.
    I agree. I have lost confidence in the mechanics ability to diagnose as well. When I couldn't solve the problem myself I had the car towed to the mechanic because they had a reputation for working on Mustangs. Tomorrow they are replacing the idle speed control and rebuilding the throttle body (it was already rebuilt last summer) because we can't find a rebuilt TBI. I don't know if this will be fix the problem…I have my doubts. I can't keep dumping money into this car even though I've had it for 32 years. If I have to have it towed home I think I need to sell it.

  3. #23
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    Quote Originally Posted by JeremyB View Post
    Derp. Yeah.
    How does this car normally at start up get fuel to the injectors? Does anyone have an answer to this question?

  4. #24
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    The fuel pump powers up for a few seconds to prime the line when you turn on the key, then comes on again once you start cranking. If you turn the key on, but don't crank the engine, you should hear it happening.
    1988 Thunderbird 5.0
    GT40P, TFS-1, KB domes, 30#, MAF conversion, Explorer GT40 Upper/Lower, Smog delete, Wide Ratio AOD Mod, Unlocked Speedo, 3G Charging System Upgrade, Hi-Torque Mini Starter, 3.73 LSD, BBK 1 5/8 unequal headers, H-Pipe.

    88 Thunderbird/Cougar EVTM
    (Thanks to Trinom for hosting)

  5. #25
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    Quote Originally Posted by sarjxxx View Post
    I'm thinking if this were the case though it would be causing a deficiency in air delivery, not fuel delivery right? Spraying alternative fuel should have no effect if its a case of not enough air making it through the TV
    Not sure why I brain-freezed in my original reply.

    Don't have the manual in front of me so I can't remember how it is supposed to function. The ISC has 4 pins. Power, +actuation (more throttle), -actuation (less throttle), and signal return which lets the ECU know the ISC is touching the throttle bracket (when the ISC touches the throttle bracket, a ground path is enabled. Might get some wonkiness if the ground isn't working. Or the TPS could be out of range. While cranking, WOT TPS voltage is a signal to not run the injectors to clear a flooded condition. The noid light results seem to refute that though.

    A 'tired' injector might have issues responding to low idle pulse widths, but the've been replaced.
    The fact that is runs fine while not idling should rule out fuel/spark availability - at least initially.

    There is a powertrain/troubleshooting manual that should have proper procedures to run through - but I highly doubt they have one.

    What is the lowest rpm that the engine will run in idle? What is the position/voltage of the ISC/TPS at this rpm? What happens when you drop below it?

  6. #26
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    Quote Originally Posted by TheFoeYouKnow View Post
    The fuel pump powers up for a few seconds to prime the line when you turn on the key, then comes on again once you start cranking. If you turn the key on, but don't crank the engine, you should hear it happening.
    Ok thanks!

  7. #27
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    Quote Originally Posted by JeremyB View Post
    Not sure why I brain-freezed in my original reply.

    Don't have the manual in front of me so I can't remember how it is supposed to function. The ISC has 4 pins. Power, +actuation (more throttle), -actuation (less throttle), and signal return which lets the ECU know the ISC is touching the throttle bracket (when the ISC touches the throttle bracket, a ground path is enabled. Might get some wonkiness if the ground isn't working. Or the TPS could be out of range. While cranking, WOT TPS voltage is a signal to not run the injectors to clear a flooded condition. The noid light results seem to refute that though.

    A 'tired' injector might have issues responding to low idle pulse widths, but the've been replaced.
    The fact that is runs fine while not idling should rule out fuel/spark availability - at least initially.

    There is a powertrain/troubleshooting manual that should have proper procedures to run through - but I highly doubt they have one.

    What is the lowest rpm that the engine will run in idle? What is the position/voltage of the ISC/TPS at this rpm? What happens when you drop below it?
    I don't have the answers to your questions but I will ask the mechanic. Thanks!

  8. #28
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    His alt fuel probably has higher a oxygen content, similar to alcohol, so that the alt fuel brings extra oxygen with it.
    What happens if you create a small vacuum leak like disconnecting the PCV valve from the throttle body?
    (might be too large a leak, maybe cover with a thumb and let the port bleed a little)
    1988 Thunderbird 5.0
    GT40P, TFS-1, KB domes, 30#, MAF conversion, Explorer GT40 Upper/Lower, Smog delete, Wide Ratio AOD Mod, Unlocked Speedo, 3G Charging System Upgrade, Hi-Torque Mini Starter, 3.73 LSD, BBK 1 5/8 unequal headers, H-Pipe.

    88 Thunderbird/Cougar EVTM
    (Thanks to Trinom for hosting)

  9. #29
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    Quote Originally Posted by TheFoeYouKnow View Post
    His alt fuel probably has higher a oxygen content, similar to alcohol, so that the alt fuel brings extra oxygen with it.
    What happens if you create a small vacuum leak like disconnecting the PCV valve from the throttle body?
    (might be too large a leak, maybe cover with a thumb and let the port bleed a little)
    Any type fuel will start the car up when manually introduced to the TBI - I've used carb. cleaner, starter fluid and 93 octane raw gas. Could bad gas in the tank cause the idling problem?
    Haven't tried removing the PCV valve to create a vacuum leak.

  10. #30
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    What we need is someone who still has the 86 PC/ED manual.
    1988 Thunderbird 5.0
    GT40P, TFS-1, KB domes, 30#, MAF conversion, Explorer GT40 Upper/Lower, Smog delete, Wide Ratio AOD Mod, Unlocked Speedo, 3G Charging System Upgrade, Hi-Torque Mini Starter, 3.73 LSD, BBK 1 5/8 unequal headers, H-Pipe.

    88 Thunderbird/Cougar EVTM
    (Thanks to Trinom for hosting)

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