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  1. #1
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    Question Engine bogs down at high RPMs! Help!!

    The other day I took my freshly built (pistons, rods, etc.) 96' cobra to the track for the first time. Every time I accelerated the car would bog down during the higher rpms and it would feel like it wasn't going anywhere.

    Could this be the clutch slipping or maybe having insufficient amount of fuel? I know that my transmission needs a rebuilt because my synchros are starting to go bad. Anyways, any advice will be greatly appreciated.

  2. #2
    Got Torque? Red98CobraStang's Avatar
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    when was the fuel filter changed last?

    Plugs?
    Wires?

    Do you smell anything when the car bogs? if the clutch is slipping you would know. It would smell terrible.

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  3. #3
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    The plugs were changed only about a month ago after I build the bottom end. I don't know about the wires and the fuel filter.

  4. #4
    Crazy SVT Poster John4cam's Avatar
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    You didn't happen to put msd coil packs on it did you? I had a problem similar with em on.

    Could be a fuel problem like said above, what kind of maf setup is on the car??

  5. #5
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    Coilpacks are stock and the maf is a C&L, not sure what size, it was already on the car when I bought it. I guess I'll start by replacing the fuel filter and inspecting the injectors.

  6. #6
    Got Torque? Red98CobraStang's Avatar
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    is the compression ratio stock?

    was the car tuned after the motor was rebuilt?

  7. #7
    Black Venom mustangsf4life's Avatar
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    Fuel filter maybe. $10 part and its worth a shot.
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  8. #8
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    The compression ratio is slightly higher but not much. No, I haven't had it tuned.

  9. #9
    Just Another Sell Out
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    do you still have the imrcs? did it feel like the car hit a wall, or did the engine rev but the car not accelerate?

  10. #10
    Crazy SVT Poster John4cam's Avatar
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    My c&l also gave me probs, try the stocker and see how it runs.

    Just trying to eliminate everything..

  11. #11
    SVT God JasonSnake's Avatar
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    Quote Originally Posted by blown4v View Post
    do you still have the imrcs? Did it feel like the car hit a wall, or did the engine rev but the car not accelerate?
    +1

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  12. #12
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    Yes I still have the IMRCs. When I took off the line, the car accelerated from 1st gear, shifted into 2nd, pedal on the floor, the rpm started climbing, then all of a sudden between around 4-6k rpm the car as you mentioned hit the wall (the pull of the car drastically decreased and I believe the rpm stopped climbing, it was like hitting the rev limiter). So I shifted into third and the same happened again. Other than that it pulls hard as hell.

  13. #13
    SVT God JasonSnake's Avatar
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    Quote Originally Posted by FLSVTCobra View Post
    Yes I still have the IMRCs. When I took off the line, the car accelerated from 1st gear, shifted into 2nd, pedal on the floor, the rpm started climbing, then all of a sudden between around 4-6k rpm the car as you mentioned hit the wall (the pull of the car drastically decreased and I believe the rpm stopped climbing, it was like hitting the rev limiter). So I shifted into third and the same happened again. Other than that it pulls hard as hell.
    sounds like a classic case of imrc syndrome

  14. #14
    SVT God brucesvt's Avatar
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    Quote Originally Posted by JasonSnake View Post
    sounds like a classic case of imrc syndrome
    +2 yep sounds like the IMRC's need cleaning. g/l and keep us posted
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  15. #15
    I build them she drives Tx_Diablous's Avatar
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    IMRC's open between 3200 to 3400 and I would think it would bog in any gear over these RPM's. Try bringing it up to these RPM's and then steadly push it up to 6,000 and see if the bog changes and you feel a drop off in the pull. There are a lot of things that can cause a bog. Fuel pump, bad coil pack, plug wires, and even a bad MAF not seeing the correct air flow can cause it. If you can data log you might be able to track it down without using the buy, replace, remove and clean and still not knowing what it is. Now having said all of that, if it seems to pull ok with steady peddle pressure I would look at the fuel system. If it bogs no matter how fast you push through 3200 then I would lean toward the MAF or the coil packs-plug wires. If it only bogs when you stomp it to the floor I would go for IMRC's.
    BTW good luck this symptom sucks and could be almost anything.

  16. #16
    4.10's or 4.30's??!! b dub's Avatar
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    Yeah I highly doubt it's your imrc's...
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  17. #17
    Got Torque? Red98CobraStang's Avatar
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    The more and more I think about this, It leads me to belive the MAF function may be to blame.

    Do you still have the 24lb injectors in the car?

    As said before, throw on the stock MAF and see what happens.

  18. #18
    SVT God crazycarlo's Avatar
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    same thing happened to me at the track a month ago. Do you happen to have an aftermarket high flow fuel pump in it or an aviator pump. Mine would hit a wall at 5-5500 rpms and come to find out it was sucking the basket dry causing a lean condition and activating the knock sensors which pulled timing. I had to drill holes in my fuel basket.... now she pulles cleanly all the way to 7.

  19. #19
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    Yeah I still have the stock 24lb fuel injectors. When I bought the car it already had a C&L maf therefore I don't have the stock one.

    I also have an aftermarket fuel pump which flows at 190lph.

  20. #20
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    Question

    Quote Originally Posted by crazycarlo View Post
    same thing happened to me at the track a month ago. Do you happen to have an aftermarket high flow fuel pump in it or an aviator pump. Mine would hit a wall at 5-5500 rpms and come to find out it was sucking the basket dry causing a lean condition and activating the knock sensors which pulled timing. I had to drill holes in my fuel basket.... now she pulles cleanly all the way to 7.
    What do you mean by "sucking the basket dry"? And "drilling holes in the basket"? What you have described is almost identical to what happened to me at the track. Could you be more specific? Thanks.

  21. #21
    4.10's or 4.30's??!! b dub's Avatar
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    The pumps sits in a basket and is sucking it dry before it can be refilled by the fuel in the tank. You drill some holes in the basket, it stays filled.

  22. #22
    Drunk Again. Cookieman00x's Avatar
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    Who tuned the car? Id check your plugs


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  23. #23
    Crazy SVT Poster John4cam's Avatar
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    Quote Originally Posted by Cookieman00x View Post
    Who tuned the car? Id check your plugs
    Good idea, should tell the story for you.

  24. #24
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    Quote Originally Posted by Cookieman00x View Post
    Who tuned the car? Id check your plugs
    The car has not been tuned since I have build the bottom-end. I will check the plugs in the next couple of days.

    Thanks for all the suggestions!!!!

  25. #25
    Terminated '98 68_GT's Avatar
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    you just had an engine built and you're dragging it at the track w/o it being tuned ?

    is it not throwing any codes ? sounds like a fuel problem to me. Does you car have a fuel rail pressure sensor ? could you have damaged anything while putting everything back together ? pinched / damaged wire ?

    I'm still hunting down a circuit malfunction from a bad wire somewhere in my car after the terminator motor went in. It bogs at higher rpms also.
    Last edited by 68_GT; 03-02-2009 at 07:32 PM.
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