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Engine light-No code

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by KILLERK5, Aug 7, 2002.

  1. KILLERK5

    KILLERK5 1/2 ton status

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    I have an 88 Blazer. Sometimes it just dies without any engine studder or any indication that it is going to die. Other times the engine light comes on and the truck runs really sluggish. I have to floor it to gain any speed. Once I turn the truck off and re-start it, she runs fine. I checked for an engine code but all it's givng is a 12, nothing after. I don't have any clue of what the problem is or what to look for, so any suggestions or experiences would be a big help!

    Thanks!!
     
  2. Thunder

    Thunder 3/4 ton status

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    The check engine light coming for a little while on then only showing a code 12 usually means the ECM is not recieving a signal from the distributor for a short time.( It wont store this in its memory)
    The cause probablaly is a bad Dist module or bad magentic pick up coil. Also check all the connections for the ignition.

    A lot of people think that a code 12 shows everything is ok. But it acually means" No Distributor reference pulses"
    Thats why a code 12 always comes up when you check the codes with the ignition on and the engine Not running.
    A code 12 also indicates that the ECM is functioning
     
  3. KILLERK5

    KILLERK5 1/2 ton status

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    Are the magnetic pick-up coil and the distribution module both inside of the distributer? How do I go about checking to see if they're bad? My Chilton's manual doesn't say anything about them.

    Thanks again!!
     
  4. Whitetrash

    Whitetrash Registered Member

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    My '87 Blazer did that too and it was caused by the distibutor module.
     
  5. 95 Silverado

    95 Silverado 1/2 ton status

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    the problem you're having is an intermittent type problem, so testing your module or pick-up won't show anything unless you can make the problem occur, as it works ok the rest of the time. I'm not one to replace parts till you find the problem, but these modules are known to cause this kind of problem and you may end up walking if you wait till it tests bad.
     
  6. alec78

    alec78 1/2 ton status

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    The reason you have no code is because the one(s) being set is/are "soft" code(s), meaning as soon as the ignition key is turned off the code is lost. The "correct" way to get the code is with some type of scan tool with the engine running after the check engine light comes on.

    If you try to do it by flash codes the engine has to be off to be in diagnostic mode. This will then produce a code 12 reguardless of any other codes that may be stored. Flash codes always start and end with a code 12, with all real stored codes flashing 3 times between the code 12. If there are no codes other than a 12 there are no codes. Per the GM service manual a code 12 is normal.

    With this in mind, the next time the check engine light comes on (granted you can do this safely) stop your blazer, pop the hood and remove power to the coil, making the engine die. Now check your flash codes. Make a note of them, and trouble shoot them in in asending order (13, 23, 33, etc.)

    Only other thing I suggest is get the GM service manual. It costs maybe $90+ but it is worth every penny! There is a trick to getting one: either get one used (Ebay is a good source) or buy one new. To buy one new you have to go to Helm Publishing (www.helm.com I think, if I am wrong send me a PM and I'll get the correct one), dealerships do not sell them normally.
     
  7. alec78

    alec78 1/2 ton status

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    Ok I read the Service Manual a little more (about 10 pages) and the code 12 DOES technically mean no signal to the ecm from the distribuitor pickup. Which (obviously) means when the engine is off this is normal. Didn't mean to step on any toes.
     
  8. Thunder

    Thunder 3/4 ton status

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    To test the dist module:
    Take the cap and rotor off the dist
    un bolt and un plug the black box you see inside
    Take it down to NAPA or most any major auto parts store. They usually will test it for free.
    I think the problem is in the module.
    The pick up coil will usually throw a code 42 when they go bad. to test them you measure the resistance between the green and white leads you see inside the dist that plug into the module. I dont rember how much resistance its susposed to have. But it tells how much in the Grey Chilton manual.
     

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