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  1. #1
    FEP Power Member fgross2006's Avatar
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    Default Fouled plugs on one side of engine - 96 Yukon

    I have a 96 Yukon, throttle body and distributor run.

    Yesterday the truck started stuttering on the parkway, then check engine started flashing. Clearly a misfire. Pulled a code P0300, Random misfire from the ECM. Took it to my mechanic and ran the SnapOn scanner and determined that all 4 cylinders on the passenger side were misfiring. Pulled the plugs and all 4 were fouled with carbon.

    Since this engine is a recent crate engine from GearHead with a warranty I need to determine if this is an internal issue. My mechanic could not find any vacuum leaks or intake leaks. All fuel injectors are firing. No exhaust leaks.

    Anybody have any idea what would cause one side of the engine to misfire and foul plugs out?

  2. #2
    FEP Super Member gr79's Avatar
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    Maybe the pass side O2 sensor (if there are 2) is sending bad signals?
    Does engine have cylinder deactivation capability?
    Just guesses

  3. #3
    FEP Power Member fgross2006's Avatar
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    Quote Originally Posted by gr79 View Post
    Maybe the pass side O2 sensor (if there are 2) is sending bad signals?
    Does engine have cylinder deactivation capability?
    Just guesses

    I was thinking that too but wouldn't there be an O2 code before the misfile started?
    The only code present is P0300

  4. #4

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    Doesnít that engine run of of coil packs in a pack grid? Loss of power or ground on one side of the grid. Or an ECU issue

    How many crank triggers does that technology use for firing the packs? If itís one per side, another possibility

  5. #5
    FEP Power Member fgross2006's Avatar
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    Quote Originally Posted by erratic50 View Post
    Doesnít that engine run of of coil packs in a pack grid? Loss of power or ground on one side of the grid. Or an ECU issue

    How many crank triggers does that technology use for firing the packs? If itís one per side, another possibility
    no coil packs, Distributor. A brand new AC Delco one also

  6. #6

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    First thing I would do is check to see if there's gas in the oil, pull the dipstick and smell, then if it smells gassy see if a lighter will light it. Next, check the fuel pressure regulator, there known to rupture, then clean those plugs with carb cleaner and blow them off.

    When checking the regulator pull the vacuum line and see if gas comes out.

  7. #7
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    Check O2 sensors and look for exhaust leak on that side.

  8. #8
    FEP Power Member vintageracer's Avatar
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    IF this is 96 it will have a Vortec 350 and that means there is a plastic spiker under the top of the plastic intake manifold. These are known to go bad. The spider directs the fuel to the injectors. There was an update setup for the spider.

    Google the "Vortec Spider" and see what you find.

    Could or could not be the cause however given the fact the problem was sudden it must be sudden failure in one of the systems on the engine. U also said new distributor. Does that mean really is new GM, really is new rebuilt or U really don't know? Did you replace the distributor car AND rotor button when this "new"distributor was installed?

    https://troubleshootmyvehicle.com/gm...uel-injector-1
    Last edited by vintageracer; 02-15-2019 at 05:39 PM.
    Mike
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  9. #9
    FEP Super Member gr79's Avatar
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    ooops is a 96 engine. duh.
    cyl de-ac just a dream back then. Computers, internet were not mainstream like now.
    Maybe a TSB on it?
    Early era OBD I, II, generic code testing could not pinpoint specific components like now.
    Not as many code lines in the PCM or something to store and monitor.
    P0300 is sort of generic, vague. Misfiring detected. That's it.
    Has to be a component that affects either bank of cyl as a unit.
    Or the fuel leaks mentioned above, but i would think all cyl would be affected by that.

  10. #10

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    Bad cap?

  11. #11
    FEP Power Member fgross2006's Avatar
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    I got rid of the misfire today. I did complete tune up. Even though this crate motor has only been in my truck for 18 months and I put all new ignition stuff in during the install I still felt I needed to start with basics.

    I found 6 plugs fouled with oil and caked on mud. The cap and rotor weren't in such great shape either. I swapped all 8 plugs, a new wire set, cap and rotor. Car runs great, no codes, no misfire. BUT. I am sure I have an internal leak dripping oil on the plugs which fouled them out so this "fix' is a band aide I think.

    I have to convince Gear Head that there is a leak internally causing plugs to foul and leading to misfire condition. The rep I spoke to on the phone yesterday was already leaning towards blaming anything other than the long block for the problem I am having. Now that the Yukon is running well, how do I convince them there is a problem worthy of warranty service? The guy wants me to do compression test which I'm not sure will prove or disprove anything. he also told me to put a vacuum gauge into the oil dip stick tube but there's no vacuum reading there at all.

    I have to call Gear Head from my mechanic's shop Monday. I hate to have to pay my guy for time to do compression testing to learn the bottom half is fine. Does anyone have any definitive tests to prove oil is leaking internally onto the plugs?

  12. #12

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    If plugs are fouled from oil there can only be one source —oil is getting into the cylinders.

    So now the question is why.

    Im thinking you may want to explore PCV related things.

    Otherwise lack of oil control is caused by the typical things - oil rings, umbrella seals, valve guides, improper seal of the compression rings or improper end gap or broke rings allowing/causing severe blowby, cracked pistons, etc

    if you can pull the pan that’s where broke rings usually end up.

    if you put a bore scope down each hole that could tell you if there is something funky going on. I’ve seen guys hone the bores so much that the rings and pistons don’t fit right

  13. #13

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    If you have a drain back issue that could pump all the oil up top and make the PCV suck it in like itís under water

    Or if the PCV is not installed properly

    Sucks trying to solve this stuff ó good luck!

  14. #14
    FEP Power Member fgross2006's Avatar
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    update on this issue;

    Just for good measure I thought I should change the PCV and found that there was none. Just an elbow pushed into the grommet the PVC is supposed to be in. That may be the source of the fouled plugs.

  15. #15

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    That is a VERY good guess at least. Let’s hope so!

  16. #16
    FEP Power Member fgross2006's Avatar
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    Quote Originally Posted by erratic50 View Post
    That is a VERY good guess at least. Letís hope so!
    I took the car to my local machine shop and asked the rebuilder what he thought. We revved the engine and there was no smoke coming out the tailpipe. The thing is that I am consuming oil too fast. I just changed the oil about 5 weeks ago and I'm a quart low as of yesterday.

    Hopefully the addition of a PCV where there was none prior will alleviate the plugs fouling but I still have to wonder why I'm consuming oil. Last oil change only 2 1/2 quarts drained out.

  17. #17

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    Holy crap!! The oil is going somewhere for sure!

  18. #18

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    Quote Originally Posted by fgross2006 View Post
    I have a 96 Yukon, throttle body and distributor run.

    Yesterday the truck started stuttering on the parkway, then check engine started flashing. Clearly a misfire. Pulled a code P0300, Random misfire from the ECM. Took it to my mechanic and ran the SnapOn scanner and determined that all 4 cylinders on the passenger side were misfiring. Pulled the plugs and all 4 were fouled with carbon.

    Since this engine is a recent crate engine from GearHead with a warranty I need to determine if this is an internal issue. My mechanic could not find any vacuum leaks or intake leaks. All fuel injectors are firing. No exhaust leaks.

    Anybody have any idea what would cause one side of the engine to misfire and foul plugs out?
    Oil control rings malfunctioning... for whatever reason of being stuck or not being installed correctly (overlap of spreader, gaps lined up) etc., not doing their job on that bank's 4 pistons. You already know she's consuming oil like a SOB, and you know it's fouling those spark plugs. What was down (oil in crankcase) is most certainly going up into combustion chambers (fouling plugs)... sounds like time to try to take full advantage of that "recent crate engine" "warranty" to me...
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  19. #19
    FEP Member bkm's Avatar
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    Those vortec engines are notorious for the intake gaskets leaking from the lifter valley under the intake. If it's one whole bank doing it, I'd definitely look in that direction.

    Sent from my SM-G960U using Tapatalk

  20. #20
    FEP Power Member vintageracer's Avatar
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    With a brand new GM crate 5.7 Vortec complete replacement long block engine assembly with a 3 year 100,000 mile GM warranty available for $1800.00 or LESS any day of the week online or at GM why would anyone purchase a rebuilt engine from a third party engine re-builder????
    Mike
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  21. #21
    FEP Power Member fgross2006's Avatar
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    Turns out they werent just fouled on one side. I pulled all the plugs found all 8 were dirty, 6 beyond use.

    I did full tune up plugs, wires, cap and rotor got the yukon running nice agai. I also noticed this truck had no PCV on the engine. the hose was jammed into the valve covers grommet with no PCV. No idea what dummy did that but I put a new PCV on and I hope thats the reason for the oil fouled plugs.

    I notified Gear head that if theres still oil consumption I will assume theres a problem with the block. Ill pull plugs in a month to check em.

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