2002 chevy-suburban 5.3 4wd p0300 Problem Need help

Discussion in 'Suburban / Yukon XL / Escalade ESV' started by kamelred408, Jan 12, 2020.

  1. kamelred408

    kamelred408 TYF Newbie

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    Hello all i am new to this forum and am looking for some help.

    2002 chevy-suburban 5.3 4wd p0300 Problem

    Parts That we have replaced with new OEM.

    All Spark Plugs
    All Spark Plug Wires
    All Ignition Coils
    All Fuel Injectors
    Fuel Filter


    I had not done those and the car has 200k Miles so i figure its about time anyways .
    I do not want to just buy parts and hope for a fix.

    I have an Autel mkx808 car scanner and can do live data and several other things with it.



    What i have found is the misfires are happening on BANK 1 only

    Cylinders 1 , 3 ,5 and 7 Misfire
    Cylinders 1 and 7 Misfire the most.

    When i drive the car it has a major loss of power and the CEL flashs at me.

    here is what i have tested so far.



    Live Data shows

    Car at operating temp and at idle
    Bank 1 Heated o2 sensor 1 Moves up and Down from 100 mv - 900 mv like normal

    Bank 2 Heated o2 sensor 1 Moves up and Down from 100 mv - 900 mv like normal

    Bank 1 Heated o2 sensor 2 Moves up and Down from 100 mv - 900 mv THIS IS NOT Normal

    Bank 2 Heated o2 sensor 2 Stays steady 750ish mv

    I thought maybe the cats where bad so i did a temp test and it seems fine im going to do another temp test tonight to make sure ill edit in the exact temps later.

    Could it be the bank 1 cats are bad and causing a misfire on bank 1?


    My fuel trims stay around 0 and move to -10
    Bank one fuel trim moves towards -10 more then bank 2





    Fuel Psi
    Checked after car sat all night 0 psi
    checked when key is turn but engine is not running 58-60 psi then starts to drop
    Checked when car is running stays stead at 60 psi

    fuel injector psi ( i have this feature on my scanner)
    All Injectors Shoots up to 67 psi then down to 44 psi ( they are all new)


    now some times after the car sits i have to prime the fuel lines to start the car so i know the pressure is dropping.

    I dont see how that would cause a misfire one bank 1 only tho.

    A new fuel pressure regulator is my next item but may need a fuel pump?


    im building a smoke tester and have not done a compression test yet.



    what could this p0300 random misfire be. its driving me crazy and i need the truck for a family trip soon.

    any and all help would be great thank you
     
  2. kbuskill

    kbuskill ***CAUTION*** I do my own stunts!

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    I am not super familiar with the GMT800 platform.

    On the GMT900 trucks there is a harness that goes between the coil packs and the main engines harness, so that you could unplug it from the main harness and remove all 4 coil packs while still attached to the bracket as an assembly.

    I have seen that harness go bad and cause the same issues you are having.

    I assume the older LS engines use the same type of harness.

    Looks like this...
    rps20200113_215815_335.jpg
    Hope this helps.
     
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  3. kamelred408

    kamelred408 TYF Newbie

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    ok thanks im doing a valve cover job on it now so ill swap them and see if miss moves to bank 2.... that is a great idea thanks bud
     
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  4. Fless

    Fless Full Access Member

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    Suspect the check valve in the fuel pump, with it not holding pressure overnight. Can you monitor the pressure after you shut it off, to see how long it takes for the pressure to go down? Document elapsed time and the resulting pressure.
     
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  5. Larryjb

    Larryjb Full Access Member

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    Intake manifold gaskets are a common failure point, and would certainly cause a misfire on one side only.
     
  6. kamelred408

    kamelred408 TYF Newbie

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    10 psi dropped in 5 min and the rest took about 30 more min



    ill spray the intake with some brake cleaner im making a home made smoke tester as well


    ill keep updated


    i took the valve cover off to make sure no lifter where stuck . all are moving the pcv was toasted so i ordered one and i broke vacuum line for it as well so have to wait until tomorrow
     
  7. swathdiver

    swathdiver Full Access Member

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    I don't think your fuel pressure problem is related to the misfires and catalytic converter performance. You can swap downstream O2 sensors but I think you have a bad cat. Now, what caused it? Might want to do compression test and maybe a leak down on Bank 1 to eliminate a bad head gasket. Any oil or coolant loss or contamination?
     
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  8. Larryjb

    Larryjb Full Access Member

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    I see now what might be happening. If you have a few injectors on the one bank that are leaking, the following may be happening.

    Both banks move to negative FT, and your fuel pressure falls. Your 2nd O2 sensors also switches. This is suggesting to me that you are getting extra fuel injected, so the fuel trims are trying to back that extra fuel. Because your FP is falling, that suggests this is real. The extra fuel is creating a rich mixture that leaves unburned fuel that the catalytic converter is unable to deal with, which is why you see the 2nd O2 sensor also switching.

    What are the long term and short term fuel trims?
     
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  9. Larryjb

    Larryjb Full Access Member

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    Oh, just in case you have two problems, pull the vacuum hose off the fuel pressure regulator and smell the hose. If you smell gasoline, that is one reason why your FP is dropping.
     
  10. kamelred408

    kamelred408 TYF Newbie

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    I broke my pcv valve hose during the valve gasket repair i am doing atm. im going to swap the o2 sensors and see if any change tomorrow when i get the new pcv and hose. i have oil leak from both valve cover gaskets but nothing else that i can see. i am going to do a compression test as well do you know the specs for this car?

    all the injectors are new and sealed. i tested them one by one with my scanner i posted the psi in org msg. but i could see how that would be a problem if they were leaking....

    my FPR and F Pump are both bad. but when the car is on it has good fuel pressure. i am going to replace both but i want to get this misfire figured out first. i like your thinking on this tho. if i had leaking injectors on that bank i think you could very well be right.




    i swapped this harness tonight while doing the the valve cover gaskets.
    once i get the car running again tomorrow i will be able to see if you are right. great thinking and thank you for this idea... i do hope it is something simple like this harness
     
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