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Need help with SES code 42

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by rh88k5, Jan 22, 2003.

  1. rh88k5

    rh88k5 Registered Member

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    Atleast 2-3 days a week my truck will stumble while cruising, then the SES light comes on. Code 42 is the electronic spark control, I know it is not my ignition module, I checked it with my spare. Any one have advice to help locate this problem? Where can I get a good wiring diagram? Anything available online? Its driving me nuts, a local shop wanted to put a new ecm in it, but I cant find any troubleshooting info on(code 42) that even mentions the ecm! /forums/images/graemlins/ears.gif
     
  2. 4x4k20

    4x4k20 1/2 ton status

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    i have the same code coming up on my 87 k20 it:s the ESC module from what i understand i am planning on changeing it out this weekend along with the map sensor [code 43] i will let you know if it helps me>
     
  3. Dunc03

    Dunc03 1/2 ton status

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    I'm actually having that same problem right now too. Except mines not computer controlled, it only and 86. Sometimes the thing starts up and runs great other times it stumbles at idle, and when you put a timeing light on it the mark jumps around anywhere from two to 20 degrees. I just rewired mine so that could be to blame, but I doubt it. I haven't fouund any good wiring diagrams on an ESC system. Chiltons has the beginnings of one, but it only traces the wires back to the ECM not the ESC module. I ordered a reproduction of the original wiring diagrams from Chevy Duty but it takes about a month and a half to get the thing, so I'm still waiting. They only go up through 86 anyways. You might try replacing your knock sensor. The system is only supposed to work at cruising speed when the engine is detecting a knock in the engine. If it does it retards the timing accordingly. If the knock sensor has gone out it maybe sending faulty signals to the module and retarding hte timing for no reasons. A sensor is only lick 12-15 bucks, so if it not that you aren't out much. hope this helps in some way.
     
  4. MudFrog

    MudFrog 1/2 ton status

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    Check your knock sensor
     
  5. Thunder

    Thunder 3/4 ton status

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    I really doubt its the ECM. I think you should find another mechanic. I would doubt the ability of someone who first advise is to replace a 200 dollar computer when there is no ECM code showing or reason to do so.
    Its probabally the magnetic pick up coil in the dist. Code 42 and stumbling/missing at cruise speed are classic symptons of a bad pick up coil.
    You have to pull the dist to change it. They usually cost no more than 30.oo
     
  6. rh88k5

    rh88k5 Registered Member

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    I dont think it is the ecm either, but I had to replace the pickup coil back in September, so I doubt that as well. I did a search for chevy engine codes and actually found a site totally devoted to code 42, it is very informative, but time consuming as well to do the tests. I do plan on doing the tests this weekend, I'll just have to brave the cold weather. P.S. most of the info on the site pointed to grounding out in the bypass circiut!
     
  7. rh88k5

    rh88k5 Registered Member

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  8. Thunder

    Thunder 3/4 ton status

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    Hmm well here.s a bit more info I hope it helps.
    Code 42 will be set when the engine is running at 600 rpm or greater, and there is no pulse on the white wire from the ecm to the ignition module for more than 200ms (milliseconds). Common causes for this code include bad connections, frayed wiring, or broken wires such as the tan/black (Timing bypass connector and ecm pin D5) purple/white( ecm pin B5) or white wire (ecm pin D4). Check your wiring carefully along with the connections back to the ecm.
    Also while you have the Ohm meeter out check the resistance between the white and green wires on the pick up coil. Should be between 500 -1500 ohms If out of those specs than the coil is not good replace it.
    Thats about all I can think of Good luck.
    PS
    Thanks for the link /forums/images/graemlins/smile.gif good info there i book marked it for future reference.
     

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