1998 K1500 Misfire help

Discussion in 'Feedback, Help and Suggestions' started by Cheyenne, Sep 7, 2017.

  1. Cheyenne

    Cheyenne Newbie

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    Just purchased a gorgeous 1998 K1500 z71, 384xxxkm 350 vortec 5.7L but has a misfire. Code reader brought back one code (p0302). Spark plug in cylinder 2 is wet. Cylinder 2 compression is 105. Cylinder 3 compression is 95 (plug was not wet). I clean MAF sensor.

    What do I need to do to fix this issue? Truck turns on every time and runs fine besides the misfire. Accelerates fine, just without as much power.
    Is this an issue that will be fixed with doing normal tune up (Plugs, wires, cap + rotor)? Need help. New to chevys and V8s. Thanks in advance.

    Also: are high performance brake calipers and rotors worth it? Or can I get same performance out of regular ones. Which material brake pads is best to use?

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  2. east302

    east302 I'm Awesome

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    Are you loosing coolant?

    Swap the plug from the #2 cylinder to another and see if the misfire follows.

    It would be helpful to have a scanner to read misfire counts. If you don't have one, you can use an app (DashCommander or CarGaugePro) with a Bluetooth OBD2 adapter (try BAFX for adapters) to get that.

    See if the #2 plug wire is damaged. Could be a worn wire or distributor cap.

    A compression test for all cylinders would be more telling, that way you could compare the highest and lowest readings. The minimum compression in any one cylinder should not be less than 70 percent of the highest cylinder.

    Factory spec is that no one cylinder should be lower than 100-psi, but your 95-psi could be an inaccurate gauge. I'd look at all eight to get a better idea and follow up with a wet test if any are particularly low to see if it is a leaking head gasket (adjacent cylinders), leaking valves or rings.

    Have you done a fuel pressure test? Spec is 60-66 psi with ignition on/engine off and it should hold for a few minutes after turning it off. If it drops, suspect a leaking injector or regulator.


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    Last edited: Sep 7, 2017
  3. Cheyenne

    Cheyenne Newbie

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    Nope, I don't have any fluid leaks at all. I ordered plugs, wires, cap and rotor, fuel filter, air filter and pcv valve. Going to put them all in when they come in and see how that goes.

    Thanks for the compression info. When I get my hands on the gauge again I will run a test on all the cylinders.
    I haven't done a fuel pressure or wet test. How do I do that?
     
  4. east302

    east302 I'm Awesome

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    Here's a video on a fuel pressure test for a 5.7L:



    Most parts stores will rent you the pressure gauge, or you can buy one. Connect the gauge, turn ignition on (without cranking it) and see what the pressure is. Watch it for a few minutes with ignition off and see if it drops.

    A wet compression test adds a little oil into the spark plug hole on suspect cylinders. Here's that procedure:

    [​IMG]


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  5. Cheyenne

    Cheyenne Newbie

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    Ok so get this. Ordered parts off Rockauto, did my distributor cap and rotors. Plugs and wires. (Plugs are not gapped)
    Now I don't have the p0302 misfire. Just the p0300 which was never there before just the cylinder 2 misfire. It is running like absolute shit. Rough misfire, wants to die and backfiring. What the heck!
     
  6. east302

    east302 I'm Awesome

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  7. Cheyenne

    Cheyenne Newbie

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    Found out the distributor cap I had got was faulty. Replaced it and I'm back at square one. So it has new plugs wires cap and rotor and still misfires cylinder 2. Going to do some spark tests on the ignition module and coil this weekend because I have those tools.
     
  8. eyesi

    eyesi Newbie

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    Cheyenne, a misfire is not spark exclusive deal, a misfire can be caused by spark, fuel, air leak, even mechanical issues. wet spark plug could be caused by No. 2 injector stuck open, or fuel pressure regulator inside plenum leaking, very common in CSFI
     

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