No spark 1990 Sierra SLE

Discussion in 'Engine Performance + Maintenance' started by Mingwro, Jul 28, 2020.

Car Parts
  1. Mingwro

    Mingwro Newbie

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    New to forum...is there an existing thread to troubleshoot no spark to plugs...thanks in advance
     
  2. stutaeng

    stutaeng I'm Awesome

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    Check for spark at the ignition coil. If no spark there check the ignition control module and pickup coil on distributer. I'm not too familiar with the TBIs, but I helped my brother's C1500 with the same problem.

    I narrowed it down to those 2 items. I think I checked with digital voltmeter in AC mode. The pickup coil is part of the distributor. Luckily for him a new distributor came with both of those 2 things already included.

    Truck started right up. Just took him longer to set the timing. Had to buy timing light.

    I hope this helps.
     
  3. Mingwro

    Mingwro Newbie

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    thanks...I downloaded wiring diagram....no spark at coil....pick up coil good...changed ignition control module and fired right up
     
  4. stutaeng

    stutaeng I'm Awesome

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    Awesome!
     
  5. PlayingWithTBI

    PlayingWithTBI Desert Old Guy

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    It's funny how many times it boils down to the ICM on these trucks, glad you found it without throwing too many parts at it. I hope you got a good quality ICM like AC Delco, Delphi, etc.
     
  6. Schurkey

    Schurkey I'm Awesome

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    An ICM can fail on it's own. Yup, it's possible.

    Fairly likely that the ICM was killed by a faulty ignition coil. The insulation on the ignition coil breaks down over time. The coil develops an internal short-circuit. The short circuit lowers resistance, increasing current (amperage) draw, and at some point, the module can't handle the amperage load so it fails.

    This may--or may not--be picked up by ohmmeter testing of the ignition coil. If it tests bad...it is bad. If it tests good...it may still be bad.

    You'd want to use an HEI-calibrated spark tester to verify the old coil can still deliver proper spark power.

    If it passes the ohmmeter tests, AND it can fire an HEI-calibrated spark tester, the coil is probably good.
     
  7. PlayingWithTBI

    PlayingWithTBI Desert Old Guy

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    Another trick is, while the engine is running, spray some water on the coil body (not the wires on top). If the engine stumbles, replace it. I had a Pertronix Flame Thrower fail at about the same time as my ICM - go figure huh? Don't know which came first but as @Schurkey said, probably the coil 1st.

    IMG_0938.JPG
     

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