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Thread: Wonít go to closed loop

  1. #1
    Senior Member hippieman9's Avatar
    Join Date:  Jan 2018

    Location:  Haw River, NC

    Posts:    262

    My VIN:    06668 81' Grey interior, 5 speed, Grooved hood. Previous owner of 16301, in 2001.

    Wonít go to closed loop

    Ok so Iíve been searching past threads and I think now I am more confused LOL. The issue I am having is when checking the CO with my dwell meter it will stay steady at ď21Ē reading 8 cyl scale. 42 if doubled for 4 cyl. (Engine warm of course)

    Anyway Iím a bit confused as to what exactly I should be checking.

    I have installed a new O2 sensor. I checked the Lambda relay, by installing a known good one, nothing changed.

    Ive confirmed the vacuum lines are all installed correctly, although I donít have a smoke machine to check for leaks.

    I wasnít sure if itís a poor fuel spray pattern I should check, or an electrical issue.


    Thank in advance.

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

    Location:  Leonardtown, MD

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    My VIN:    03572

    New sensor so now I think you have a missing ground on the engine harness. Most common you missed a ring terminal that should bolt to the engine head.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  3. #3
    Senior Member hippieman9's Avatar
    Join Date:  Jan 2018

    Location:  Haw River, NC

    Posts:    262

    My VIN:    06668 81' Grey interior, 5 speed, Grooved hood. Previous owner of 16301, in 2001.

    I have also checked the grounds on the passenger side of the intake, all looks good.

  4. #4
    Senior Member hippieman9's Avatar
    Join Date:  Jan 2018

    Location:  Haw River, NC

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    My VIN:    06668 81' Grey interior, 5 speed, Grooved hood. Previous owner of 16301, in 2001.

    Quote Originally Posted by Bitsyncmaster View Post
    New sensor so now I think you have a missing ground on the engine harness. Most common you missed a ring terminal that should bolt to the engine head.
    I know there is a cluster of wires on the driver side and the one short black wire on the passenger side, with the spade connector, they are all attached and look good.

  5. #5
    Senior Member Bitsyncmaster's Avatar
    Join Date:  May 2011

    Location:  Leonardtown, MD

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    My VIN:    03572

    Pull the blue bulkhead connector and stick it back on. That connector has two ground pins that ground the lambda ECU.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  6. #6
    Senior Member hippieman9's Avatar
    Join Date:  Jan 2018

    Location:  Haw River, NC

    Posts:    262

    My VIN:    06668 81' Grey interior, 5 speed, Grooved hood. Previous owner of 16301, in 2001.

    Quote Originally Posted by Bitsyncmaster View Post
    Pull the blue bulkhead connector and stick it back on. That connector has two ground pins that ground the lambda ECU.
    Ok will do. Unfortunately i wonít be able to till I get home from work

  7. #7
    Member
    Join Date:  Apr 2017

    Location:  Houston

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    My VIN:    1890

    Although you replaced the O2 sensor, you still might want to verify the sensor input to the ECU. It should rise to about a half-volt after warmup.

    I haven't done it myself, but perhaps you could also disconnect the full-throttle/thermal-switch input to the ECU to make certain they aren't overriding the ECU operation.
    Robert
    1981 DeLorean #1890
    1976 Datsun 280Z
    1968 Pontiac Le Mans convertible

  8. #8
    Senior Member hippieman9's Avatar
    Join Date:  Jan 2018

    Location:  Haw River, NC

    Posts:    262

    My VIN:    06668 81' Grey interior, 5 speed, Grooved hood. Previous owner of 16301, in 2001.

    Quote Originally Posted by DMC1890 View Post
    Although you replaced the O2 sensor, you still might want to verify the sensor input to the ECU. It should rise to about a half-volt after warmup.

    I haven't done it myself, but perhaps you could also disconnect the full-throttle/thermal-switch input to the ECU to make certain they aren't overriding the ECU operation.
    Where do I check the O2 sensor input? Volts on the wire from the sensor ? Sorry for the dumb question.

  9. #9
    Member
    Join Date:  Apr 2017

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    My VIN:    1890

    Sorry, I can't remember exactly where I did that. I may have had a splice somewhere that let me tap into it. I'll try to have a look later to see if I can remember.
    Robert
    1981 DeLorean #1890
    1976 Datsun 280Z
    1968 Pontiac Le Mans convertible

  10. #10
    Delorean Guru
    Join Date:  May 2011

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    Club(s):   (DMA)

    There are a lot of possible reasons the system won't go into "closed loop". First make sure the frequency valve is buzzing. If it isn't buzzing it can never get into closed loop. Make sure the motor is warmed up and the WOT micro is not "set" or closed. Check that there are no vacuum leaks. If the motor hasn't been tuned up for a while (or you don't know how long it's been) it needs a tune-up. If the mixture is way off, and it doesn't take much, a 1/2 turn one way or the other, it can keep you from getting into closed loop. Finally a bad connection anywhere between the Lambda ECU and it's sensors or the frequency valve can prevent closed loop. There are specific tests you can perform to try to force the system into different pulse ratios. Refer to D:04:15 in your Workshop Manual.
    David Teitelbaum

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