High compression question

Discussion in 'Engine & Drivetrain' started by ajgreen, Aug 7, 2019.

  1. iamdub

    iamdub Hold on... Lemme overthink this for a bit...

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    Any chance both compression gauges are inaccurate? Unless I need to know the actual PSI of the cyliners (which then I'd use a known accurate gauge), I use compression gauges pretty much just to get numbers for comparing all the cylinders to see if any have a considerably different reading, regardless of the actual number. A failed injector could cause a misfire, it's not just an ignition-related issue. Unless your '99 has the injectors replaced/upgraded to the newer injector setup, it'll have poppet nozzles with a "batch fire" injector pod. The fault could be within this module.
     
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  2. SUBURBIAN

    SUBURBIAN All GM

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    Cranking compression is subjective and not directly proportional to static compression. In other words 190 to 200 psi of cranking compression does not indicate 13 point something static compression. Internal engine measurements and cam timing, even battery and starter "strength" determine static compression. Cranking compression is more of an indicator of an engines health and snappiness. 190 to 200 is normal for an L31.


    A big question here is the condition and type of injector spider. Poppets leak and can cause the black box to think misfire. Same for the distributor. The drive gears knife edge from wear and can allow enough slack with the cam to misfire. These may be where the problem is considering the even compression readings.

    What injection setup is in it, the older pressure actuated poppet setup or the newer electronic setup?

    Have you ever changed the distributor gear?

    And otherwise, that engine really needs oem ignition parts to work right. They just don't run right on anything else.

    If none of this solves your problem you might check the health of your fuel system.
     
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  3. ajgreen

    ajgreen TYF Newbie

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    Well, I took it in for a diagnostic. They told me it was a bad intake manifold gasket. They quoted me $1500! I ordered a gasket kit and an upgraded spider injection kit for $300. My weekend will be shot.
     
  4. SUBURBIAN

    SUBURBIAN All GM

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    Which gaskets? If they arent the rubberized metal gaskets send them back.
     
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  5. ajgreen

    ajgreen TYF Newbie

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    They're Fel-pro and they are indeed rubberized metal.
     
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