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Strange flat spot or surge at 1800 to 2/2500 rpm

This is a discussion on Strange flat spot or surge at 1800 to 2/2500 rpm within the General Help forums, part of the LSx Technical Help Section category; Hi there got a Vt Calais 99 mod Ls1 auto Anyway notice this bloody flat spot replaced O2 sensors Tps ...

  1. #1
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    alantic silver
    99 vt calais ls1

    Angry Strange flat spot or surge at 1800 to 2/2500 rpm

    Hi there got a Vt Calais 99 mod Ls1 auto
    Anyway notice this bloody flat spot replaced
    O2 sensors
    Tps
    Fuel filter
    Cleaned maf
    And cleaned all the earth cables to the body
    Still have plugs and leads to do which will be this wk but it will rev and idle so maybe not that!
    I have noticed if u use auto lik a manual and go through the gears problem gone or if it's cold in the morning it's gone this is really getting to me now as it isn't giving me any codes . it will rev out all the way and idle lik a gem but what is this 200 to 500 rpm I'm losing its lik a choke then comes bak I've notice if I keep acc throught it it seem to get worst or go past it but I think it causes pinging aswell any help would be good
    Last edited by muzza304; 06-20-2011 at 07:58 PM.

  2. #2
    Smiles for 9.5 Years cammed goat's Avatar
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    Phantom Black Metallic
    2004 GTO M6

    How is your fuel pump? Have you checked your fuel pressure?

  3. #3
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    alantic silver
    99 vt calais ls1

    Seems ok revving all the way out but worth a look it feels electrical to me as soon as it hot it's happens maybe coolet sensor I dunno all guess,s now

  4. #4
    Smiles for 9.5 Years cammed goat's Avatar
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    Phantom Black Metallic
    2004 GTO M6

    Check your coolant sensor then. Check the harness going to your coolant sensor as well.

  5. #5
    Mustang Eater Ls_won's Avatar
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    Maroon
    2000 z28 6 speed

    Check your coils!! they can cut out at certain RPM.
    2001 B4C Totaled 4/25/11
    2000 Z28 M6 Cammed N' Slammed (SVT KLR)

  6. #6
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    alantic silver
    99 vt calais ls1

    Ok well spk plugs and leads replaced but still has hesitation but it's moved up revs around 2000 to 2300 but only now and then so I stopped car after hot and checked coil and found 8 and 6 are sparking on the coil bolts which make me think that's the problem as it revs fine after the cough moment so stay tuned as saving for coil at moment

  7. #7
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    NBM
    1998Z28

    Your probally running 2.73 rear gears. I always noticed a flat spot when I ran that gear ratio back when the car was stock. If thats the case a set of 3.73s will take care of it. If you really want to get going get you a 3200 Vigalante convertor.
    TSP 347 SB, TSP Stage 2.5 PRC LS6, TSP MS4, Performabuilt Stage 2 4L60E, Yank PT4000, 4.11s, Fast 90/90, FTRA Cold air intake+all the free mods, Dynatech Supermaxx Exaust System, DMH Cutouts, Hooker Catback/FTRA Tips. Tuned by RPM/Garner NC. 11.28@119

  8. #8
    Mustang Eater Ls_won's Avatar
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    Maroon
    2000 z28 6 speed

    coils can act different at idle to RPM range. they can become weak enough to almost clip out when the sparking is required faster. plus you only checked 2

  9. #9
    Smiles for 9.5 Years cammed goat's Avatar
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    Quote Originally Posted by muzza304 View Post
    Ok well spk plugs and leads replaced but still has hesitation but it's moved up revs around 2000 to 2300 but only now and then so I stopped car after hot and checked coil and found 8 and 6 are sparking on the coil bolts which make me think that's the problem as it revs fine after the cough moment so stay tuned as saving for coil at moment
    Cracked coils?

  10. #10
    Mustang Eater Ls_won's Avatar
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    2000 z28 6 speed

    I'm thinking coils too

  11. #11
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    alantic silver
    99 vt calais ls1

    well took coils off and checked for any signs of hot spots but relised ths problem is when hot or cold im lost now im thnking still should replace coils just costing a heap now anyone else with ideas

  12. #12
    Smiles for 9.5 Years cammed goat's Avatar
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    Phantom Black Metallic
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    Replace coils 6 and 8 and keep us posted.

  13. #13
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    alantic silver
    99 vt calais ls1

    ok ended up getting a tuner to look at ls1 and found 2 injectors blocked up and seals cracking ended up being an easily fix hope this helps

    and coils are fine cheers for the help anyway

  14. #14
    Smiles for 9.5 Years cammed goat's Avatar
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    Phantom Black Metallic
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    Good to hear. Enjoy that Holden!!!

  15. #15
    dbl clutch'n like i shld WICKEDLS1's Avatar
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    sebring silver
    Y2K SS CAMARO

    damn and i was just about to say take it to a tuner

  16. #16
    Member denegrader's Avatar
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    midnight blue metalic
    2001 camaro z28

    Wink

    Trying to learn, Isn't a tuner basically a mechanic who specializes in troubleshooting complex fuel injection? cars not just LS-1's but all fuel injection cars can prove hard to find where faults are without tons of experience with certain cars ect?
    Now basically they charge what mechanics charge ?
    Cracking seals indicates heat and age deteriation so with these complex systems now 13 years and older other injected cars older troubleshooting can be the main issues?





    Quote Originally Posted by muzza304 View Post
    ok ended up getting a tuner to look at ls1 and found 2 injectors blocked up and seals cracking ended up being an easily fix hope this helps

    and coils are fine cheers for the help anyway

  17. #17
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    99 Formula

    disconnect your maf and drive around and wait till it get up to operating temp to make your decision , i have to replace my maf , only hiccups at 1500-2000 when up shifting and driving easy but its so annoying and noticeable . I disconnected the maf and drove it , perfectly fine and no misfires and runs great .

  18. #18
    Member denegrader's Avatar
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    midnight blue metalic
    2001 camaro z28

    Now that makes no sense to me at all i figure that the maf is looking for a density quanity quality of air ?
    To me it would say that ecm senses no air as its unplugged it would just idle maybe or shutdown maybe, thats the difficulty of computer controlled fuel injected cars from just my 2 cents worth?




    Quote Originally Posted by Ramairetransam View Post
    disconnect your maf and drive around and wait till it get up to operating temp to make your decision , i have to replace my maf , only hiccups at 1500-2000 when up shifting and driving easy but its so annoying and noticeable . I disconnected the maf and drove it , perfectly fine and no misfires and runs great .

  19. #19
    Smiles for 9.5 Years cammed goat's Avatar
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    These cars can run with a disabled MAF on their "Speed Density" programming from the factory. If I recall, though, the car cannot run past a certain RPM. Someone will give better info soon.

  20. #20
    Member denegrader's Avatar
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    midnight blue metalic
    2001 camaro z28

    2 cents worth well didnt even know these cars speed density protocol ,mapping versus mass air measured air makes sense though that they revert to mapping just to keep running till ya fix em right?



    Quote Originally Posted by cammed goat View Post
    These cars can run with a disabled MAF on their "Speed Density" programming from the factory. If I recall, though, the car cannot run past a certain RPM. Someone will give better info soon.

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