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

  1. #51
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    Quote Originally Posted by Bitsyncmaster View Post
    I agree you should get the wire disconnected to trouble shoot if it's the temp switch or the lambda ECU bad. Most owners probably won't attempt to remove a pin from the lambda ECU connector (although it's not hard to do with experience). You could also disconnect the wire at the bulkhead connector but those female pins are hard to pull from the connector. Another option is to cut the wire and then join it back when your testing is done.

    Since your holding that 54 degree dwell it must be the temp switch or lambda ECU bad.
    I'm working on getting back to this issue. I still have some hunting when I start that smooths out in about a minute or two. I'm still getting a dwell reading of around 54 with little fluctuation. I'm about to borrow someone else's lambda ECU to see it the reading changes.

    Is the wire from the CO2 to the lambda ECU suppose to show a voltage? I put a multimeter on the wire where it connects to the wire going directly to the ECU. I didn't read any voltage. I will say that I may not have set the multimeter to the right setting (200ma) or perhaps it was not grounded properly. I also found a small cut in the wire. It looks like a few strands may have been cut. The CO2 sensor is fairly new, replaced last year.
    Shannon

  2. #52
    Senior Member NckT's Avatar
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    If the lambda switch is closed, the ecu will always default the frequency valve to dwell of 54, regardless of what the O2 sensor signal is, so replacing the ecu with another one is very likely to give you the same result. So try the following test:

    .....on a hot engine, disconnect the wot and check to see if you get continuity between pin 7 and pin 5. This will determine if the lambda switch is open or closed. It should be open circuit on a hot engine........
    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....

  3. #53
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    Quote Originally Posted by NckT View Post
    If the lambda switch is closed, the ecu will always default the frequency valve to dwell of 54, regardless of what the O2 sensor signal is, so replacing the ecu with another one is very likely to give you the same result. So try the following test:

    .....on a hot engine, disconnect the wot and check to see if you get continuity between pin 7 and pin 5. This will determine if the lambda switch is open or closed. It should be open circuit on a hot engine........
    I was looking at the wide open throttle (WOT) microswitch. It has two "plungers" in it. I believe the top one if for the automatic transmission kickdown (my car is auto). The lower one is for the lambda. The lower plunger is pushed in and will not move while the upper one freely moves when depressed. Can the lower one be the problem and is there a way to lubricate it or fix it so that it freely moves?
    Shannon

  4. #54
    Senior Member NckT's Avatar
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    Quote Originally Posted by lazabby View Post
    I was looking at the wide open throttle (WOT) microswitch. It has two "plungers" in it. I believe the top one if for the automatic transmission kickdown (my car is auto). The lower one is for the lambda. The lower plunger is pushed in and will not move while the upper one freely moves when depressed. Can the lower one be the problem and is there a way to lubricate it or fix it so that it freely moves?
    Possibly. Try the following test:

    .....on a hot engine, disconnect the wot and check to see if you get continuity between pin 7 and pin 5. This will determine if the lambda switch is open or closed. It should be open circuit on a hot engine.....

    If you disconnect the wot switch and the dwell operates as normal, you've narrowed it down to the stuck-on wot microswitch. Electrical switch cleaner should help unstick it and clean the contacts.

    Trust me

    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....

  5. #55
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    If a micro switch is stuck it will stick again. They are not expensive so just replace it. In the meantime just disconnect it and see if you can get into "closed loop" ie, the dwell fluctuates.
    David Teitelbaum

  6. #56
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    Quote Originally Posted by David T View Post
    If a micro switch is stuck it will stick again. They are not expensive so just replace it. In the meantime just disconnect it and see if you can get into "closed loop" ie, the dwell fluctuates.
    I unplugged the microswitch, took the car for a drive to get it warm. When I got back I put a dwell meter on it and it fluctuated normally. It was within normal range so now I know the microswitch needs to be replaced. I still have the hunting when I first start that disappears suddenly in about a minute. Could this be the lambda ECU? I borrowed one to switch out if I need to test this.
    Shannon

  7. #57
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    Shannon, more info, photos and links for those microswitches here: http://dmctalk.org/showthread.php?13...-Switch-Wiring


    Sept. 81, auto, black interior

  8. #58
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    It is normal for the motor to hunt for a moment when first started and cold.
    David Teitelbaum

  9. #59
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    Quote Originally Posted by NckT View Post
    If the lambda switch is closed, the ecu will always default the frequency valve to dwell of 54, regardless of what the O2 sensor signal is, so replacing the ecu with another one is very likely to give you the same result. So try the following test:

    .....on a hot engine, disconnect the wot and check to see if you get continuity between pin 7 and pin 5. This will determine if the lambda switch is open or closed. It should be open circuit on a hot engine........
    Nick, You were right. It turned out to be the wide open throttle switch. I unplugged it and go the normal swing on the dwell meter. Turned out it was within normal range. I need to replace the WOT.

    I started the car this morning and it still hunts when cold. Need ideas of what to look for.
    Shannon

  10. #60
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    Quote Originally Posted by David T View Post
    It is normal for the motor to hunt for a moment when first started and cold.
    A few monts ago before I had to replace my injectors the engine did not hunt when cold. The car started right up and had a steady idle.
    Shannon

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