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Thread: Code 36 in 1987 Corvette

  1. #1
    Carb and Points!
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    Code 36 in 1987 Corvette

    Hi Guys,

    long time lurker, first time poster :)

    As the tittle suggests, I'm chasing a Code36 in my 1987 Corvette, which is a MAF Burn Off error

    I purchased the MOATES ALDU + CABL1 and loaded up Datamaster software and it all worked so easily.
    So a big thankyou to those guys for their product.


    I’ve found the following information:
    The ECM waits 5 seconds after ignition-off to start the MAF burnoff. The burnoff lasts 1 second. The ECM shuts down 11.3 seconds after ignition-off. The burnoff test starts 0.3 seconds after burnoff starts. The ECM make 6 voltage measurements and all 6 must be within the voltage window to pass the error code 36 test. On my car that window is 0.4 volts to 1.90 volts.

    However, the data I’m getting out of the ECM doesn't reflect that.
    Even though I can SEE and hear the burn off take place the data doesn't seem to be getting to the ECM. (or incorrect data is).
    I've done all the trouble shooting as per the Factory manuals and bulletins and its all as it should be, but the code persists.


    Code:
     
    
    Time Stamp Ign Volts RPM FP Volts AFGS
    Secs Volts RPM Volts gm/Sec
    41.128 13.7 775 13.6 9
    41.256 13.6 800 13.6 9.3
    41.384 13.7 775 13.6 9.2
    41.512 13.6 775 13.6 9
    41.64 12 925 13.6 8.9
    41.768 0 925 12.2 8.3
    41.896 0 0 12.4 6.7
    42.024 0 0 12.1 5.1
    42.152 0 0 12.4 4.4
    42.28 0 0 12.3 6.8
    42.409 0 0 12.2 7.2
    42.521 0 0 8.6 23
    42.649 0 0 0.6 23
    42.777 0 0 0 23
    42.889 0 0 0 23
    43.001 0 0 0 23
    43.113 0 0 0 23
    43.225 0 0 0 23
    43.337 0 0 0 23
    43.449 0 0 0 23
    43.561 0 0 0 23
    43.673 0 0 0 23
    43.785 0 0 0 23
    43.897 0 0 0 23
    44.009 0 0 0 23
    The above data shows when I turn off the ignition switch and you can see the rpm drop to zero, then you can see when the fuel pump relay goes to zero volts, but the MAF output (AFGS) goes to “23” and stays there.
    It should record the burn off “voltages” as this is the input from the MAF to the ECM.
    I didn't show all the data (post 5 seconds after shut down) as it doesnt change at all from the last line

    My question is:
    Are you aware of any impediment or changes that happen to the OBD1 connector in the vehicle once you turn off the ignition?
    Does it “lose power” of some type which means I can no longer see what the ECM is seeing?
    Do you have any idea why it goes to “23”?

    Thanks for your help

  2. #2
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    Without looking at the code, I can only guess that the engine is not running so the maf sensor value is no longer being updated. One test would be to ask someone else with a MAF car and '165 ecm to check the same conditions. What happens if you return the key to "on?"

  3. #3
    Carb and Points!
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    Because the MAF signal is being limited by the max airflow vs rpm table which happens to be 23 gm/sec at 400 rpm and below (0 rpm).

  4. #4
    Carb and Points!
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    I have the same problem. I've gone through the troubleshooting flow chart and arrived at bad computer. Since i can see the wire glow red hot for a second after the engine is shut off, I know the burn-off is happening. It seems to me the computer is not detecting it. I'm thinking of purchasing a refurb computer from autozone and see if the swap eliminates it.

    Has anybody else done this and seen the error code go away?

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