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Trouble codes 12 and 42

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by KILLERK5, Jun 11, 2002.

  1. KILLERK5

    KILLERK5 1/2 ton status

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    I just put a new 383 stroker in my 88' Blazer and my check engine light keeps coming on. It runs really nice untill the light comes on, and then it runs really slugish and needs alot of gas to get going. Im getting codes 12 and 42 every time I check, but I don't know exactly what they are.
    Code 12 is no engine speed reference pulse, I can't find anything in my Chiltons manual about a sped sensor.
    Code 42 says that the ECM has seen an open or grounded EST (Electronic Spark Timing) or bypass circuit. I don't know what this is indicationg either. I don't want to start guessing aout what the prolem(s) is and waste money on tryin to get it fixed. Any ideas or opinions would be greatly appreciated. Thanks a bunch!!!
     
  2. Chris Demartini

    Chris Demartini 1/2 ton status

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    <font color="blue">Code 12 means that it's in diagnostic mode and/or there is no distributor reference signal to the ECM. Check the conector on the back of the distributor to see if its loose or corroded. If it's good, I guess the next step would be to check for continuity between the pins of the said connector and the corresponding pins on the ECM connector. Anyone got a factory service manual?
     
  3. BurbinOR

    BurbinOR 3/4 ton status

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    GM Codes Reference has all the codes you'll ever need for all the systems.

    Check your grounds........
     
  4. Burbinator

    Burbinator 1/2 ton status

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    Great reference...thanks!
     
  5. MudFrog

    MudFrog 1/2 ton status

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    Does the enging ping a lot before the check engine light comes on? If so check the knock sensor... I had to replace mine, but you just described the problem I had.
     
  6. YtseJam

    YtseJam 1/2 ton status

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    I have found that the oem knock sensor is very sensitive. When you modify the engine it seems to always pick up a KS signal and throw the EST into Bypass. Try pulling the wire off of the Knock sensor and see if it changes.
     
  7. Blazer_Boy

    Blazer_Boy 1/2 ton status

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    Whats the profile on the cam you have in there? What kind of vacuum do have at idle? An aftermarket chip may help some issues. The computer probably doesn't like the fact that it has to feed 33 extra cubes and a camshaft that it didn't come with.
     

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