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Thread: Lamda not working

  1. #11
    Senior Member DMCVegas's Avatar
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    Workshop Manual Section D:04:14 will lay everything out and give you the exact specs you should be seeing.

    LAMBDA has 3 modes of operation for target duty cycles it applies to the Frequency Valve:
    • The first is Open Loop for when the O2 sensor is offline because it is not yet warmed up. 40-50 Steady Reading
    • The Second is for when Enrichment is triggered. This occurs when the LG, or Light Green wire is grounded. Both the WOT switch and the Thermal Switch in the Y-pipe are spliced into this same wire and can trigger this by WOT or coolant temp of 15C/59F or less. 50-60 Steady Reading
    • The third and final is normal operation. O2 Sensor is reporting back, and neither the WOT or Thermal Switch is triggered. 35-45 Pulsating


    If you want to test the LAMBDA ECU, you can do it easily once it's warmed up. Ground the O2 lead and it'll hit 87 minimum. Apply 1.5V and it'll hit 20 maximum. That'll let you know if it's bad or not. Just in case too, disconnect the WOT Switch, and then check the LG wire to see if it's grounded. That'll tell you if the Thermal Switch is bad and screwing with things by constantly running too rich when not needed. Of corse, check all grounds as well. For the hell of it, also gently snug up the 3 brass screws to ensure there are no leaks. Probably not related, but it's good to ensure you're not running unbalanced cylinder banks.


    Quote Originally Posted by David T View Post
    I have found that the cars with the "hotter" cams need a little bit higher idle speed to be happy. Try bumping it up by opening the brass air screws.
    How does that work exactly? Not trolling here at all, but genuinely curious. Any amount of additional metered airflow you supply would increase idle speeds, yes. But once the RPMs increase, the Idle Speed Circuit is going to see that and adjust the Idle Speed Motor accordingly to drop the speeds back down to defeat said modification to the RPMs.
    Robert

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  2. #12
    Senior Member Bitsyncmaster's Avatar
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    The problem with our stock O2 sensor is the fact it's not heated. That's mostly why all the newer cars have heated O2 sensors now. They found the lower RPM at idle that sometimes the sensor is just to cool to provide a good output. Maybe the higher lift duration cams run cooler (don't know). Maybe some of our idle hunting problems are caused by that.

    You can run a higher closed loop idle RPM with my idle ECU or a modified stock ECU. Any other adjustments will make the idle RPM go open loop.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  3. #13
    Senior Member NckT's Avatar
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    Quote Originally Posted by David T View Post
    I have found that the cars with the "hotter" cams need a little bit higher idle speed to be happy. Try bumping it up by opening the brass air screws. You may not get the dwell to read 35-45 for a good idle either. It may take a bit richer mixture to get it to run smooth at idle too.
    How many have you done exactly? I've set up 3 with the stage 1 dmch and 1 with just the performance cams and have not had to increase the rpms from stock all with the brass screw modification I outlined in another post.
    RIP Rob van de Veer Top bloke

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  4. #14
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    Quote Originally Posted by NckT View Post
    How many have you done exactly? I've set up 3 with the stage 1 dmch and 1 with just the performance cams and have not had to increase the rpms from stock all with the brass screw modification I outlined in another post.
    Exactly 2. Opening the brass screws bypasses control of the idle motor. The more air you allow around it (through the air screws) the less control it has and the less ability it has to reduce the idle speed. Cars went to the heated O2 sensors mostly to reduce the time of the warm-up cycle to control the emissions quicker. The other reason is to prolong the life of the sensor so it doesn't get contaminated from raw fuel as easily. What base timing were the cars running when you got the idle set?
    David Teitelbaum

  5. #15
    Senior Member NckT's Avatar
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    Quote Originally Posted by David T
    Exactly 2. Opening the brass screws bypasses control of the idle motor. The more air you allow around it (through the air screws) the less control it has and the less ability it has to reduce the idle speed. .........
    No it doesn't, as it is dependent on how far you open the brass screws. I explained this in post no.19 in
    http://dmctalk.org/showthread.php?15...umpiness/page2

    The advance for all were set to 14-14.5 deg btdc vacuum isolated, apart from one car that I set up at the last euro fest (in a car park) where the timing was 13btdc.

    I don't want this to get off topic from the original post.
    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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    Reopening old threads seems to be current de jure, so here we go. Michael's descriptions and at least the diagnostic steps here lead me to choose this particular thread.

    What I'm actually chasing is high idle (about 975) but the car based upon different attempts to measure it, is not going into closed loop (or at least, very rarely).

    Last year, I replaced all the vacuum lines, O2 sensor, and have also put additional clamps on suspect vacuum leak spots, as well as replacing injector
    seals, etc. This spring, I pulled my manifold for painting and expressly to check the vacuum routing in the valley - all fine.

    I can't hear it, but I'm assured my FV is working. I've checked physical and electrical operation of idle and WOT switches, and recently also checked
    the butterfly valves are closing fully. I do have DM's idle ECU (set to 775) which has the LED read out for closed loop mode which is obviously not coming on, and
    for completeness, I've hooked up the "A/C bump" (as an aside, this has largely eliminated my stalls when coming to a stop), but obviously for testing no A/C is running.

    The car has no cold start, hot start or other issues, and general seems to run exceptionally well given everything. What I will do shortly is pull the vacuum canister;
    I know its hoses aren't always in good shape, and easy to check.

    In any case, suggestions on things to things to measure, check (or hell, triple check). Nothing immediately jumps out at me from the thread, apart from perhaps
    measuring the O2 sensor reading.

    Thanks!

  7. #17
    Senior Member Bitsyncmaster's Avatar
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    Quote Originally Posted by MrChocky View Post
    I do have DM's idle ECU (set to 775) which has the LED read out for closed loop mode which is obviously not coming on, and
    for completeness, I've hooked up the "A/C bump" (as an aside, this has largely eliminated my stalls when coming to a stop), but obviously for testing no A/C is running.

    Thanks!
    The LED turning on indicates the idle motor is fully closed so it can't reduce idle any more. With the LED off it indicates the idle motor still has range to control idle speed. If it is still off and your still indicating high RPM then it may be your ignition is missing making the ECU think it's running a lower RPM. Verify the idle motor is buzzing when engine is at idle (you can feel the idle motor and feel vibration).
    Dave M vin 03572
    http://dm-eng.weebly.com/

  8. #18
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    Subscribed for future. Good info here!

  9. #19
    Administrator Ron's Avatar
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    Quote Originally Posted by MrChocky View Post
    Reopening old threads seems to be current de jure, so here we go. Michael's descriptions and at least the diagnostic steps here lead me to choose this particular thread.

    What I'm actually chasing is high idle (about 975) but the car based upon different attempts to measure it, is not going into closed loop (or at least, very rarely).

    Last year, I replaced all the vacuum lines, O2 sensor, and have also put additional clamps on suspect vacuum leak spots, as well as replacing injector
    seals, etc. This spring, I pulled my manifold for painting and expressly to check the vacuum routing in the valley - all fine.

    I can't hear it, but I'm assured my FV is working. I've checked physical and electrical operation of idle and WOT switches, and recently also checked
    the butterfly valves are closing fully. I do have DM's idle ECU (set to 775) which has the LED read out for closed loop mode which is obviously not coming on, and
    for completeness, I've hooked up the "A/C bump" (as an aside, this has largely eliminated my stalls when coming to a stop), but obviously for testing no A/C is running.

    The car has no cold start, hot start or other issues, and general seems to run exceptionally well given everything. What I will do shortly is pull the vacuum canister;
    I know its hoses aren't always in good shape, and easy to check.

    In any case, suggestions on things to things to measure, check (or hell, triple check). Nothing immediately jumps out at me from the thread, apart from perhaps
    measuring the O2 sensor reading.

    Thanks!
    Didn't re-read it all, so stabs in the dark:
    Ensure the three brass screws are shut.

    Perform all of the procedures (record, and post if off) at D:04:15/5.

    Record where the CO screw is currently at. Then nudge it in steps, as small as you can one way, until it about dies or starts swinging. If no luck, try the other direction.

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