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Thread: Engine breaks up over 2000 rpm's

  1. #1
    Join Date
    Dec 2007
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    6

    Engine breaks up over 2000 rpm's

    I have a problem that I can't figure out and would love some advice. I recently purchased a 1991 SC with and automatic trans. The previous owner told me that he was on the highway and this problem started like someone flipped a switch. The car starts no problem and runs up to around 2000 rpms no problem. When I stomp on the gas the car immediatly falls on its face. and breaks up like the timing is off or somthing. I was working on it the other night and noticed that the exhaust was glowing really bright up to the central muffler. ( I think thats what it is at least) The 2 cats and headers were glowing also) I thought that maybe the cats were blocked up so I disconected the exhaust at the headers but that didnt change anything. I have already changed the maf, throttle position sensor and coil with no improvment. Could the Dis control module go bad and cause any of this? I was gonna change the camshaft sensor next but I am getting sick of spending money with no Idea whether it will help with my problem. As far as I know it is not a fuel issue. The fuel pressure stays at alittle over 40psi and never drops. I think it is supposed to raise at high rpms but the car wont rev up that high for that to be the problem. The person I bought the car from said it could be the computer. any advice will be greatly appreciated! One more thing that is confusing me is that the boost still climbs when the rpms drop. Im not familiar with this kind of blower. I have a cefrifugical blower on my mustang and the boost is directly assosiated with the rpms of the motor. curious to know what the difference is.

  2. #2
    Join Date
    Aug 2005
    Location
    Sunrise Beach, MO
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    2,289
    it sounds like a vac leak, try starting it and spraing starting fluid around the IC joints and such, the intake and intake plenum, or propane is another thing to use, or you can buy a tool deal from www.spinningwheels-sc.com that pressurizes your intake tract to check for leaks,

    hope i helped a little bit

    -Tony-

    PS have a good new year

    PS where do you live
    [B][COLOR="Blue"][COLOR="Red"]June 6, 2009....D-Day[/COLOR][/COLOR][/B]
    [B][COLOR="Blue"]1989 SC AUTO- Midnight Blue:D[/COLOR][/B]
    "They act like they are bed buds that have known me forever" -Corey B-

  3. #3
    Join Date
    Dec 2007
    Posts
    6

    Tried that already

    I used a propane cylinder to check all of the vacum lines and didnt notice any surge in rpm's It is very possible that I missed a line or2. Does anyone have a vacum line chart? im From Long Island NY in case anyone knows of a good SC mechanic in my area.
    Last edited by slowsc; 12-31-2007 at 05:10 PM.

  4. #4
    Join Date
    Jan 2003
    Location
    Columbia, SC
    Posts
    3,468
    Check and see if the crankshaft pulley is wobbling with the engine running and report back. Sounds to me like your timing is off due to a broken harmonic damper.
    22 year SC Owner GFP
    (Glutton for Punishment)
    1992 5 Speed SC one of 1256
    1995 5 Speed SC one of 574

  5. #5
    Join Date
    Oct 2004
    Location
    Charlotte, NC
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    8,159
    I was going to suggest the same thing.....

    One way to check for vacuum leaks......

    Get a piece of vacuum hose and put one end in your ear and probe around with the other end.....

    If there is a vacuum leak, you will be able to hear it.....

    Check all around the intake and IC tubes.....

    Get yourself some teflon IC gaskets, that should help rule out that area for leaks.....

  6. #6
    Join Date
    Oct 2006
    Location
    va beach,va
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    2,585
    I would suggest doing some EEC tests before throwing anymore parts at it. Do both key on engine off (KOEO) and key on engine running (KOER) with a EEC-4 compatable scanner and see if you get anything pointing towards fuel control (Maf, maf connector, hegos) or ignition control (crank position sensor, dis module, camshaft position sensor). This really should always be the first thing done during driveability diagnosis.

  7. #7
    Join Date
    Jan 2003
    Location
    Columbia, SC
    Posts
    3,468
    Without a CEL it is doubtful reading codes will buy you anything...but do as you want.
    22 year SC Owner GFP
    (Glutton for Punishment)
    1992 5 Speed SC one of 1256
    1995 5 Speed SC one of 574

  8. #8
    Join Date
    Oct 2006
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    va beach,va
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    True, However no Cel doesnt mean there are no codes stored in memory or that one can't be produced during the snap test of the KOER. If not you could always check datalogging short and long term fuel trim to verify fuel control is correct and move on from there...that would rule out the vacuum leak theory and point toward DIS, CKP, CPS problem.....

  9. #9
    Join Date
    Jan 2003
    Location
    Columbia, SC
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    And how would you propose he do datalogging on a 91 SC and what is he going to use to get fuel trim numbers?
    22 year SC Owner GFP
    (Glutton for Punishment)
    1992 5 Speed SC one of 1256
    1995 5 Speed SC one of 574

  10. #10
    Join Date
    Oct 2006
    Location
    va beach,va
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    2,585
    nevermind........
    Last edited by frdlvr30; 01-01-2008 at 03:38 AM. Reason: I dont know what im talking about

  11. #11
    Join Date
    Oct 2006
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    va beach,va
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    Duffy has all the answers....after all he has owned a mn-12 for 18 years....nevermind us guys who were actually fixing them for all those years......
    Last edited by frdlvr30; 01-01-2008 at 03:44 AM. Reason: Ask the administrator

  12. #12
    Join Date
    Aug 2004
    Location
    Edmonton, Alberta
    Posts
    834
    Now this might sound silly but I had a car that had the glowing cats and it turned out I had a bad plug so the fuel was getting into the exhaust and burning. I was also shooting flames out the exhaust and it would stutter with moderate throttle. Why not pull the plugs to see what condition they are in maybe that will lead to other suggestions. Does the car backfire or anything else? with the front section of the exhaust off is there any fluid comming out of the pipes?

    John

  13. #13
    Join Date
    Apr 2002
    Location
    Queens, NYC
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    Quote Originally Posted by Duffy Floyd View Post
    And how would you propose he do datalogging on a 91 SC and what is he going to use to get fuel trim numbers?
    Spiro (aka the original slowsc) was able to get datalogging out of the 89-93 computers..


    slowsc what part of Long Island are you from? Im in West Babylon every weekend at my buddy's shop.. We are SC junkies.. I can help you find the problem

  14. #14
    Join Date
    Nov 2004
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    Brantford, ON
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    Quote Originally Posted by Duffy Floyd View Post
    And how would you propose he do datalogging on a 91 SC and what is he going to use to get fuel trim numbers?
    Duffy, I'm currently doing that with my '90 and the EEC Tuner board . Talk to Dave D and ask him about some of the information I've been giving him as I've been tuning my car.

  15. #15
    Join Date
    Jun 2002
    Location
    Hamilton, Ontario
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    My guess is bad fuel pressure regulator, or the vacuum hose connecting it has come off.

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