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Thread: Engine Hunts at Start and Then Rough Idle When Warm

  1. #1
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    Engine Hunts at Start and Then Rough Idle When Warm

    My problems started a few weeks ago. The engine was running very well except for a minor hot start issue. I had the injectors cleaned. Now the
    engine hunts when first starting for about a minute. I assume it does this while the cold start injectors is active. Here is a video of it hunting and then suddenly stopping:
    https://youtu.be/4FEjgP0si2U

    The idle once warmed up is rough. I've been trying to put a dwell meter and check the idle but no matter which way I adjust the screw the dwell reading does not change. Could the CO plug be bad? Here is a video after the engine has warmed up.

    https://youtu.be/6QxHJeUyQsE

    What do I need to fix?
    Shannon

  2. #2
    Senior Member Bitsyncmaster's Avatar
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    Cold start injector only fires when the starter is turning.

    You probably need a mixture adjustment after your injectors were cleaned. But if you don't get any dwell reading you may have a component failure. Is your FV buzzing?
    Dave M vin 03572
    http://dm-eng.weebly.com/

  3. #3
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    Hi Shannon - what dwell are you reading ? from the ignition ???



    Didn't you install an EFI some years ago when you asked people how the idle works ?

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    Quote Originally Posted by Bitsyncmaster View Post
    Cold start injector only fires when the starter is turning.

    You probably need a mixture adjustment after your injectors were cleaned. But if you don't get any dwell reading you may have a component failure. Is your FV buzzing?
    It seems to be buzzing as it feels like it when I place my hand on it.
    Shannon

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    Quote Originally Posted by Elvis View Post
    Hi Shannon - what dwell are you reading ? from the ignition ???



    Didn't you install an EFI some years ago when you asked people how the idle works ?
    I don't have the EFI anymore. I have the stock engine now. The dwell meter is hooked to the diagnostic plug by the firewall. You can see it in the video.
    Shannon

  6. #6
    Senior Member Bitsyncmaster's Avatar
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    Quote Originally Posted by lazabby View Post
    I don't have the EFI anymore. I have the stock engine now. The dwell meter is hooked to the diagnostic plug by the firewall. You can see it in the video.
    If the FV is buzzing you should be reading some dwell. There is a two pin connector with an orange wire and purple wire on your engine harness. The orange wire is what connects to the diagnostic port. You can also read dwell right off the FV wire.
    Dave M vin 03572
    http://dm-eng.weebly.com/

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    My diagnostic plug is further down ond the left and black and not visible on the video !?!?!?!


    BTW - I only use an oscilloscope for these adjustments, just in case you know someone...


    Didn't you say that EFI is much easier, more fuel efficient and gets you more power ?
    What was the reason to go back to stock ?

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    Quote Originally Posted by Elvis View Post
    My diagnostic plug is further down ond the left and black and not visible on the video !?!?!?!


    BTW - I only use an oscilloscope for these adjustments, just in case you know someone...


    Didn't you say that EFI is much easier, more fuel efficient and gets you more power ?
    What was the reason to go back to stock ?

    If you get a dwell reading, any reading, and it doesn't change, it means you are in "open loop" where the ECU is outputting a fixed dwell. You need to get the ECU into "Closed Loop", that is where it responds to changes from the O2 sensor and adjusts the frequency valve accordingly. If you are stuck in open loop the motor hasn't warmed up, or a senor is bad or disconnected.
    David Teitelbaum

  9. #9
    Voice For Hire Farrar's Avatar
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    I would check the oxygen sensor for proper function.
    DeLorean status: 3.0L installed and running

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    Member NckT's Avatar
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    Disconnect the oxygen sensor electrical connection at the rear firewall on the drivers side under the wooden board (follow the 4mm ish thick blue cable from the fuel computer). Once done, the frequency valve should then buzz and the dwell should be 45deg / 50%

    If it is then the oxygen sensor is not working or you simply haven't adjustex the mixture far enough and the dwell is at saturation resulting in the frequency valve not buzzing (most likely)

    If it isn't then there's a problem with the operation of the fuel computer so check fuse no.7 and the lambda relay for correct type

    Good luck
    RIP Rob van de Veer Top bloke

    I say Sir, I must be mad, one loves fixing K-Jet !

    Make sure there's plenty in the tank for the weekend chaps....

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