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Engine stumbles at 2K rpm stops at 3K

This is a discussion on Engine stumbles at 2K rpm stops at 3K within the General Help forums, part of the LSx Technical Help Section category; My LS1 consistently feels like it is missing or stuttering or something. It happens in any gear between 2K and ...

  1. #1
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    navy blue metalic
    199 Firehawk

    Engine stumbles at 2K rpm stops at 3K

    My LS1 consistently feels like it is missing or stuttering or something. It happens in any gear between 2K and 3k rpm. Not detectable above or below that range.
    I cannot hear anything different and it is real subtle, like all of a sudden the acceleration curve has a bunch of little dips.

    Plugs and wires were done recently and problem came long after the change. Otherwise the engine has 136K miles and is still strong. Lot's of fun on a track day!

    Thoughts?

  2. #2
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    WHITE
    2000 WS6 T/A

    Clean your MAF with MAF cleaner. K and N filter oil can be a culprit too. Just a suggestion.

  3. #3
    Royal pain in the.... Phantom2kz's Avatar
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    2001 Z-28 A4 NBM
    2002 35th anni SS M6#1696

    also check your fuel filter,and pressure
    make sure no leaks to air induction, M.A.F. to throttle body.
    Slower Traffic Keep Right...........

  4. #4
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    navy blue metalic
    199 Firehawk

    cleaned the MAF earlier, pretty sure my air intake tubes are tight, I did put the stock air cleaner back on because the ls1 tech seemed to contribute to overall engine noise, perhaps I should swap back?

  5. #5
    Junior Member nevrfastenough01z's Avatar
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    black
    2001 Camaro Z28

    did you check the sensors on the intake?

  6. #6
    Moderator 35th-ANV-SS's Avatar
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    Did you check fuel pressure like suggested? Sounds like fuel pressure loss to me. Is it throwing any codes?

  7. #7
    Veteran 0rion's Avatar
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    98 Formula
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    what mods do you have?

  8. #8
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    I had a similar problem with my car. It seemed to idle fine, but stumble shortly off acceleration almost like it dropped a couple cylinders, but if I put my foot to the floor, instantly it was back to normal, and would drive fine for a bit, but then start again. But always ran perfect at wide open throttle. Turns out my 02 sensors were getting lazy throwing the fuel trims out of whack and flooding the engine at odd times. If this sounds like your problem, replace both your upstream 02 sensors (in front of the catalytic converters, the ones behind are just for emissions) it's not a bad idea anyhow at that mileage, you'll likely pick up a MPG or two if your current ones are old.

  9. #9
    Member 4thGenTA's Avatar
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    2002 firebird trans am

    bad fuel? are you using 91+ octane

  10. #10
    O U 8 1 2 Spaz's Avatar
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    you said you changed the plugs and wires then this started happening shortly after... i'd assume either a plug is cracked or you got a bad plug wire... make sure all the boots and pushed in all the way also...

  11. #11
    Member JRENIGAR's Avatar
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    99 camaro

    Mine does this also. Just recently started after changing the plugs. I had it scanned at autozone with their cheap scanner and it said code 300 random miss fires detected but didnt say if it was just one cylinder or more??? Any tips?? It runs fine once warm but wont idle for more than 5 to 10 secs at a time when cold. It idles ok warm but something is still wrong. It kind of half way misses from time to time??? Help please.

  12. #12
    Something Diabolical... chuckie669's Avatar
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    Wear a glove or something to protect from the heat and put a finger on each plug wire on the top of the boot. First feel at the spark plug end by touching the top of the boot then to the coil pack by touching the underside of the boot. If you feel a tapping, either the spark plug is not tightened correctly or the boot is not snug.

    and by touching I mean use your finger and put a slight pressure on the boot on the top where the wire goes into it.

  13. #13
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    Using your finger to check for spark can be quite painful sometimes. Use a spray bottle with water in it, just spray a fine mist around the plug wire boots, and you'll see the spark if it's escaping.

  14. #14
    Member JRENIGAR's Avatar
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    99 camaro

    I checked all the plugs n wires. It seems to be running really rich at idle. I pulled all the 02 sensors and a couple of them are making a rattling sound when I shake them and some arent. I believe the sensors are on their way out and Im going to replace them tomorrow and will report back when I know more.

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    Cool, I look forward to hearing what happens. Don't be discouraged if it does it again after changing the sensors. It may take a few good trips for the computer to get the fuel trims back into a reasonable range. Unless you have access to a good quality scan tool, you could reset everything back to defaults, but it's not necessary, as it will re-learn by itself.

  16. #16
    TunedbyFrost.com Tuner Frost's Avatar
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    Quote Originally Posted by MonteLS1 View Post
    ... Unless you have access to a good quality scan tool, you could reset everything back to defaults, but it's not necessary, as it will re-learn by itself.
    or just unhook the battery for a few seconds...

  17. #17
    Member JRENIGAR's Avatar
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    red
    99 camaro

    car does seem to be idling better and running better but still has a miss or two evry few seconds at ilde. Will try to disconnect the batt and see if that fully cures the prob. Its almost like a small vaccum leak somewhere that I cant hear or find??? I have put over 100 miles on it and no ses light yet even with no converters on it.

  18. #18
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    Well I'm happy to hear that you've at least solved something. But it still might get better. If you still suspect a vacuum leak, just get like a 2 foot length of some type of hose and put it to your ear and listen around, especially at the back of the intake, they have a few vacuum lines back there.

  19. #19
    Member JRENIGAR's Avatar
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    99 camaro

    ^^^ good idea. I sprayed brake cleaner around the tb and front of the intake manifold while it was running cold, but no luck. It starts right up, but runs rich enough when It idles a bit and I get on it theres a big cloud of blue smoke behind the car till it gets some rpm then it goes away??? Has me stumped??? Might check fuel press reg. If it went bad could it be possible that its keeping more press than its supposed to??? That would cause a rich at idle condition, wouldnt it???

  20. #20
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    Quote Originally Posted by JRENIGAR View Post
    ^^^ good idea. I sprayed brake cleaner around the tb and front of the intake manifold while it was running cold, but no luck. It starts right up, but runs rich enough when It idles a bit and I get on it theres a big cloud of blue smoke behind the car till it gets some rpm then it goes away??? Has me stumped??? Might check fuel press reg. If it went bad could it be possible that its keeping more press than its supposed to??? That would cause a rich at idle condition, wouldnt it???
    It's very possible. When the engine is warm it could compensate using the O2 sensors for too much fuel. But when the engine is cold, the O2 sensors are ignored until they warm up, and the computer runs the engine on a default setting that determined from the previous run cycle. So it would have no way of knowing if it's too rich until it is warm. Regulated fuel pressure should be around 58 psi I believe. Could be a leaking fuel injector also. This is a bit of a confusing one. It would be nice to get a scan tool on it and have a look at a few things.

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