Distributor experts, a ? on TBI dists

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by jimmy88, Mar 13, 2003.

  1. jimmy88

    jimmy88 1/2 ton status

    Feb 17, 2002
    Likes Received:
    Detroit, MI area
    Noticed the cap terminals have the arc marks off to one side so I did the old hole in the cap and watch the rotor with the timing light thing. At idle the spark looks to be jumping when the leading edge of the rotor blade is even with the leading edge of the terminal on the cap or even a little before. Disconnect the brown wire ( 0 degrees ) and the spark happens when the trailing edge of the rotor blade is about 3/4 of the way across the cap terminal.

    Question is what is the max advance on the TBI set up and when is it programmed to occur? Didn't the old mechanical distributors advance the rotor with the centrifugal advance to keep the rotor blade pointing at the cap terminal? I have the feeling I'm missing something here, but what?
  2. Thunder

    Thunder 3/4 ton status

    Jul 20, 2000
    Likes Received:
    Northeast Nevada
    The advance in a TBI dist is controlled totally electronically by the computer. Total advance will occur when the computer says it can. It all depends on input from the various sensors on how much advance it runs.
    I,m not sure how much advance the stock chip has programed in it.Proly around 30- 32 degrees.
    Usually at idle without the timing bypass wire disconnected a TBI engine will run from 16 to 22 degrees advanced depending on where the base timing is set and what the sensors tell it.
    You can raise the base timing from the 0 mark a little without screwing things up and it may perform a little better. I set my base timing around 4 degrees advanced with no problems. If you set the timing/advance too high you may start getting Knock sensor codes (43).

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