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Vortec 8100 Issue...

This is a discussion on Vortec 8100 Issue... within the GM Trucks forums, part of the Vehicle Specific category; It's stuttering and hesitating randomly at various throttle openings. It starts and idles just fine. Sometimes it stutters right off ...

  1. #1
    Senior Member Tobynine9's Avatar
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    Vortec 8100 Issue...

    It's stuttering and hesitating randomly at various throttle openings. It starts and idles just fine.

    Sometimes it stutters right off idle like a carb that's way too rich and is bogging out. Sometimes it doesn't.

    It's starting to stutter and hesitate and higher speeds now. Example - rolling along at 60, accelerate to pass, 4L85E downshifts and the motor starts hiccuping.

    I think it's getting worse.

    I already swapped out the Crankshaft Position Sensor - apparently that's a common problem for '02 8100 equipped 2500s. No change.

    I swapped the fuel filter. No change.

    I cleaned the MAF and made sure the intake plenum was properly secured. No change.

    Anyone got any ideas?


    Edit: The vehicle is a 2002 Avalanche 2500 - 4x4, 8100, 4L85E, etc. Just hit 100k miles.

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    Member 00ls-1's Avatar
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    no ses light?

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    Member 00ls-1's Avatar
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    the platinum plugs usually go between 80k and 100k miles

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    Senior Member Too Fast's Avatar
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    Sure sounds like a plug/wire issue. Try looking at them at night, see if you see any light shows, there should not be any. Or try misting them with a water bottle while idling. If it's all golden, nothing will happen when the water hits it.

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    Senior Member Tobynine9's Avatar
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    No SES light.

    Plugs are new NGK V-powers.

    Wires are young Taylor 10mm.

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    Member 00ls-1's Avatar
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    what about coil packs? air filter clean?

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    Senior Member Too Fast's Avatar
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    This engine has the coil-near-plug setup like our LS1s? And it just started after or before the new plugs/wires? If after, my bet is a wire or two is not snapped on all the way. They will feel like it, but take them apart and try again. Many here have been fooled.

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    Member 00ls-1's Avatar
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    you coulda got bad gas too

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    Veteran 0rion's Avatar
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    I'm going to agree with the others that said it sounds like an ignition issue or it could be leaning out too I guess. Have any way to log it and look at things like fuel trims and misfire counts? Would at least put you on the right track.

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    Member 00ls-1's Avatar
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    i had a 6.0 in a 2500 truck.....just rememeredit had an injector go out and thats what it did 2 different times
    they also make 2 different length wires for those motors you might have got the short and need the long so they arent making good contact

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    Senior Member Tobynine9's Avatar
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    Air filter is clean.

    The 8100 does have coil-near-plug ignition. It's basically a 454 stroked to 496 with a few tweaks here and there to allow a Gen-III style ignition.

    I re-gapped the plugs just now. We'll see tomorrow if that helps. For some reason I thought I read that opening the gap from stock was the "plug-gap mod". Turns out, you're supposed to narrow the gap. I dropped the gaps from .65'ish to .45'ish.

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    Senior Member Tobynine9's Avatar
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    If that doesn't help or clear it up I'll check fuel pressure at the rails. If that's good then it's off to someone with a proper scan/diagnostic machine to get the full run-down.

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    Senior Member Tobynine9's Avatar
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    Meh, it's still doing it.

    I think I've described the problem somewhat wrong. It's not really a misfire or a stutter. It's more of a loss of power. As you accelerate it sort of bogs out - rrrrRRRRRR buuuuuu RRRRR.

    At higher engine speeds it just feels like a stutter as its happening quickly - RR bu RR bu RR bu RR bu, etc.

    Gonna check fuel pressure tonight.

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    Quote Originally Posted by Tobynine9 View Post
    Meh, it's still doing it.

    I think I've described the problem somewhat wrong. It's not really a misfire or a stutter. It's more of a loss of power. As you accelerate it sort of bogs out - rrrrRRRRRR buuuuuu RRRRR.

    At higher engine speeds it just feels like a stutter as its happening quickly - RR bu RR bu RR bu RR bu, etc.

    Gonna check fuel pressure tonight.
    How many miles on the vehicle? Possibly a plugged converter?

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    Senior Member Tobynine9's Avatar
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    100k miles.

    I guess it maybe could be a problem with the catalytic converter... 8100s use a lot of oil. This motor is no exception.

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    Member 00ls-1's Avatar
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    I'm still gonna say it's probably an injector

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    Senior Member Too Fast's Avatar
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    Did it just start after you changed the plugs/wires, or is this something you did to try for a fix?

    Is your MAF clean? That would cause some drivability issues you (newly) describe.

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    Senior Member Tobynine9's Avatar
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    MAF is clean. Did that already.

    I changed the plugs in response to the problem. It hasn't helped.

  19. #19
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    put your hand up to the tailpipe and have someone rev on it...if you cant feel much air movin, then most likely the cat is plugged.

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    Senior Member Tobynine9's Avatar
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    It's not a clogged cat. You can feel a strong pulse on both exits just by walking past them.

    I'm starting to fear it may be a dying fuel pump.

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