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Thread: Lamda not working

  1. #1
    Motors about after dark Michael's Avatar
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    Lamda not working

    So after noticing a hard cold start(sometimes it would start right up cold, other times it would take about 5 or 6 seconds of cranking before it started), checked CSV operation. I went to look for any obvious vacuum leaks, none that I could see. I then attached my dwell(engine warm enough for closed loop) to see if it was rich and no activity(right on 50%) on the o2 sensor at all. I replaced the o2 sensor and still dead dwell needle although it is rich, barely fluctuating a little(probably because of the cam) and does change with throttle, but no real o2 signal that I can see. The car does start, idles, runs fine, but the o2 signal is just not there. However there has been once or twice in the past few days of me finding a few minutes to work on it that it does work and mixture is set perfect. I am thinking maybe my lambda computer is bad. The WOT switch works, the o2 sensor is new, idle circuit is working. FV is fairly new and seems like its working. Right now I am just waiting on the engine to cool and maybe dive deeper to find a vacuum leak. As far as I can tell the thing is stuck in open loop and has only went into closed loop like twice during my messing with it. This is a stage II engine (cams, headers, etc.)

    Is the temp switch on the water pump housing the only thing that tells the lamda system to work?
    Last edited by Michael; 09-30-2017 at 04:49 PM.

  2. #2
    Senior Member NckT's Avatar
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    The switch on the water pump is the thermo-time switch and this only operates the cold start valve etc.

    I'll assume your frequency valve is buzzing and you've connected your dwell meter ok and set it to 4 cylinder seeing (not 6 cylinder) etc.

    There is a switch on the V pipe under the Ubley manifold and this has the lambda switch, ie it is closed when the water temp is approx less than 80c and open when the engine is warm etc. This closed switch is an input to the fuel computer to operate a fixed dwell at 54 deg/about 60%. This is in parallel to the full load throttle switch so if you're getting this dwell value, try disconnecting the full loaf throttle switch as it's not unknown for them to stick in the closed position.

    If your'e only getting a fixed value of 45deg /50% dwell then it could be likely that the oxygen sensor signal is not switching/ voltage input that would be enough for the ecu to operate. This would be the case if you do get a varying dwell if you run the engine at 3000-3500 rpm. In this condition it would clearly indicate a bad oxygen sensor.

    If the above is not true, then connect an oscilloscope to the oxygen sensor signal wrote to the fuel ecu and if it gives a sinusoidal voltage change between 0.2v to 0.8v at 1hz idle but no varying dwell then I'd check the connection to the evu input or try another fuel computer

    Good luck, I hope it's something simple.
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  3. #3
    Senior Member Bitsyncmaster's Avatar
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    I'm pretty sure what tells the lambda to go closed loop is voltage from the O2. There is no voltage when the O2 sensor is cold.

    You can try unplugging the lambda connector and plug it in again just in case there is a marginal connection.

    I have a few lambda ECUs that I have tested as working. If you want to borrow one to test.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  4. #4
    Not a DeLorean Guru
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  5. #5
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    To get into "Closed Loop" the temp senor must cycle and the O2 sensor must be putting out enough voltage. Of course that is assuming everything else is working. If you are getting a reading at all we can assume the Lambda ECU is getting power and if you hear the freq valve buzzing it is connected and working. There are tests you can do to the ECU to verify operation. See the notes in the Workshop Manual. The O2 sensor puts out a very low voltage so if you ANY bad connections between it and the ECU, or you do not have a GOOD ground the Lambda ECU will not get the signal from the O2 sensor.
    David Teitelbaum

  6. #6
    Senior Member Bitsyncmaster's Avatar
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    Your blue bulkhead connector pins 22 and 23 have to go to engine block. Those are two grounds going to lambda ECU

    22 B Engine block, from Lambda ECU pin 5
    23 B Engine block, from Lambda ECU pin 16
    Last edited by Bitsyncmaster; 09-30-2017 at 06:19 PM.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  7. #7
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    Something free and easy to also check is the O2 sensor (reference) ground. It is (usually) attached to the block on the passenger/forward side, sort of near where the frequency valve is. The short length of wire that is screwed into the block is RED and then has a black quick connector on it that connects to the longer, regular black ground wire that eventually meets up and gives the O2 sensor it's ground reference. Check to see if that connection is good.

    Shown in photo (I relocated mine slightly higher as I have a small chunk of broken off screw in the hole it is supposed to go in).

    O2 sensor ground.jpg


    Sept. 81, auto, black interior

  8. #8
    Motors about after dark Michael's Avatar
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    Thanks for all the advice, I definitely have plenty to check. FWIW I do think it is going into closed loop now. I started it fairly cold and hooked my meter up and watched until it went closed loop. As soon as it did the engine wants to die, so I think any signal I should see gets lost with the engine starving:



    I am leaning heavily towards a vacuum leak after seeing that, but then about a minute later (see next post, only one vid allowed per post these days I guess)
    Last edited by Michael; 09-30-2017 at 07:00 PM.

  9. #9
    Motors about after dark Michael's Avatar
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    About the :25 mark you can see how the engine shudders at the starve point. It has always had a bit of a lope to it because of the cams, but this was a bit more pronounced. I think I need a few cans of carb cleaner and start looking under the intake for a leak. I'm just not seeing enough action from the O2 (which is brand new BTW) and I did take it out and drive it to burn off any impurities before this.
    Last edited by Michael; 09-30-2017 at 07:03 PM.

  10. #10
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    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.
    David Teitelbaum

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