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Thread: Engine running rough cannot set mixture

  1. #1
    Member Dhennick99's Avatar
    Join Date:  Jun 2011

    Posts:    36

    Engine running rough cannot set mixture

    Car was sputtering bad. Had it floored and it would barely go. I had an aftermarket Bosch idle motor installed previously. So I swapped back in the factory idle motor and it was still doing it. I had the factory ecu installed, but Dave Mckeen's updated version on hand. I jumped the ecu diode, backed out the throttle screw and installed Dave's ecu. I also set the curb idle using the on-board led on Dave's ecu. When I went to set the fuel mixture the dwell needle wouldn't swing at all. Frequency valve isn't buzzing either. Car starts and the dash rpm needle continually hunts. The rpm will drop so low that it stalls out while hunting. Attached is a photo of where the dwell meter sits.


    20210112_162450.jpg

  2. #2
    Senior Member Bitsyncmaster's Avatar
    Join Date:  May 2011

    Location:  Leonardtown, MD

    Posts:    8,043

    My VIN:    03572

    The RPM relay turns the lambda system on by powering the "main fuel relay" (lambda relay). First is make sure that lambda relay is the correct type. If you have no FV buzz still then you need to start checking for a bad RPM relay, connection to lambda relay and connections to FV and lambda ECU.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  3. #3
    Under Ron's watchful eye. Glory be to Ron! Michael's Avatar
    Join Date:  May 2011

    Posts:    4,200

    My VIN:    A bunch of numbers and letters that should not interest you.

    A little backstory or history would prove most helpful.

  4. #4
    EFI'd dn010's Avatar
    Join Date:  Jul 2011

    Location:  Florida: Pinellas County

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    Check the condition of your bulkhead connectors.
    -----Dan B.

  5. #5
    Member cis6409's Avatar
    Join Date:  Jul 2011

    Location:  ireland

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    My VIN:    6409

    Club(s):   (DOC-UK) (DOI)

    Get the frequency valve working first , car will never run right with it not functioning.
    As Michael says, a little backstory info would help..
    Last edited by cis6409; 01-13-2021 at 11:09 AM.
    only from the past can we choose the correct path for the future...

  6. #6
    Member Dhennick99's Avatar
    Join Date:  Jun 2011

    Posts:    36

    Bulkhead connectors were solid. I don't know what else there is to tell as far as backstory. The car just started the spuddering without warning or anything leading up that would be identifiable as cause.

    The hunting issue has been going on ever since the spark plugs were done. Perhaps something was disturbed. I checked vaccum lines and everything appears to be connected properly.

  7. #7
    Delorean Guru
    Join Date:  May 2011

    Location:  Northern NJ

    Posts:    7,861

    My VIN:    10757 1st place Concourse 1998

    Sometimes the non-functioning frequency valve can be as simple as a bad connection with the connector plug to the valve. Take the connector off and put it back on a few times and see if that helps. Another thing that can stop it from buzzing is if the mixture is WAY off. A stuck plunger in the mixture unit can do that. A bad Lambda relay can prevent power getting to the Lambda ECU and running the frequency valve. If you are getting a reading, any reading at all, on your dwell meter, it means the ECU is getting power and the relays are not the problem. Without the frequency valve buzzing, it is not adding any fuel to make the A/F ratio correct so you are running very lean, that's why you don't have any power and it won't idle. The mixture screw sets the base mixture and the frequency valve adds what is necessary to get the correct mixture. Do not try to adjust the mixture screw to "fix" this. Get the frequency valve to buzz. Is the muffler getting red hot? That means the mixture is WAY too rich and the plunger is stuck. If the muffler isn't red hot you are running too lean and the plunger isn't stuck but the frequency valve isn't working, it's probably an electrical problem. There is a small ground wire that goes to the intake manifold to ground the frequency valve. See if you knocked it loose.
    David Teitelbaum

  8. #8
    Member Dhennick99's Avatar
    Join Date:  Jun 2011

    Posts:    36

    The muffler isn't getting red hot. Richening the mix won't engage the frequency valve? The ground is intact.

  9. #9
    Delorean Guru
    Join Date:  May 2011

    Location:  Northern NJ

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    My VIN:    10757 1st place Concourse 1998

    OK, we're getting somewhere. We know the ECU is getting power and the mixture is lean. Try doing and undoing the plug on the frequency valve a couple of times. If that doesn't get the valve to buzz, next is to check the O2 sensor.
    David Teitelbaum

  10. #10
    EFI'd dn010's Avatar
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    Location:  Florida: Pinellas County

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    Correct me if I'm wrong (since I haven't messed with K-jet in many years since my swap), but can't you just trip the full throttle microswitch in order to force the FV on, to at least check it for operation to rule out electrical/connection problems?
    -----Dan B.

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