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Computer Advanced Timing

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by 87BrnRsd, Jul 5, 2003.

  1. 87BrnRsd

    87BrnRsd 1/2 ton status

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    Does anyone know how much the computer in my 87 K5 can adjust the timing? It was running really rough, until I pulled the dist and rotor since they were about 100 degrees off. I fixed it, and it runs good now. But I was looking at it today, and realized the rotor is still off 1 notch. Can the computer adjust this? Thanks for the help.
    -Harrison
     
  2. SUBFAN

    SUBFAN 1/2 ton status

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    Are you positive it is still off? Then make it right....
     
  3. 87BrnRsd

    87BrnRsd 1/2 ton status

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    I will, but I dont have the time right now, or the access to the truck. I was just wondering to see if the computer could fix it, and make it un noticable, since the truck runs good.
    -Harrison
     
  4. GQ 350

    GQ 350 Registered Member

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    In my expirence with the computer controlled engines, I have heard of the ECM (Engine Controll Module) correcting the timing for the distributer being out. However the engine will run poorly and sometimes backfire. Most of the ECM engines require the timing to be set at 0* at top dead center #1 cylinder. But in the end the ECM can make up for it being out, but I wouldn't leave it like that for too long /forums/images/graemlins/pimp1.gif /forums/images/graemlins/truck.gif
     
  5. 87BrnRsd

    87BrnRsd 1/2 ton status

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    Yes, it does sometimes backfire. And I am planning on setting the timing correctly before I drive it again.
    -Harrison
     
  6. HarryH3

    HarryH3 1 ton status Author

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    The computer on your truck has NO idea where top dead center is. There's no input for that on older EFI rigs. It just gets a pulse from the pickup coil in the distributor each time a plug needs to be fired. Based on input from the TPS, MAP sensor, Engine Temp sensor, etc., the computer just looks up a value stored in a table and provides that many degrees of timing advance. The program assumes that the base timing has already been set correctly, as it doesn't have any way to know for certain. If the Knock sensor reports pinging to the computer, then it will retard the timing a couple of degrees at a time, until the knock stops. But if your timing was off 100 degress, then the engine wouldn't have run, as the computer doesn't have a clue how to compensate for base timing that is not correct.
     

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