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Thread: Shudder / buck in 3rd gear

  1. #1
    Join Date
    Nov 2012
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    Charleston, SC
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    89

    Shudder / buck in 3rd gear

    I have a 90 SC 5 speed. Transmission rebuilt several years ago and ran fine. Car sat for about 4 years (about 2,000 miles put on it during that time). Recently I started driving more and noticed when shifting that as long as it's a slow easy shift through each gear at low rpm's, there is no problem. If you shift more aggressively, such as accelerating onto a highway, the car will buck / shudder initially in third gear, then accelerates fine. The buck can be harsh (you can hear engine knock) if you're accelerating hard. Any thoughts on what may be the culprit?

  2. #2
    Join Date
    Dec 2007
    Location
    Salem OR
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    7,501
    These cars don't like sitting... 4 yrs? How old is the fuel?

    Typical suspects when mentioning bucking are plugs/wires. Then perhaps fuel pressure, fouled/leaking injectors, vacuum leaks, bad engine grounds, crummy fuel, plugged cats...lots of things that can cause misfire individually or in concert with other problems.

    Did you run the codes yet?

  3. #3
    Join Date
    Nov 2012
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    Charleston, SC
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    Quote Originally Posted by KMT View Post
    These cars don't like sitting... 4 yrs? How old is the fuel?

    Typical suspects when mentioning bucking are plugs/wires. Then perhaps fuel pressure, fouled/leaking injectors, vacuum leaks, bad engine grounds, crummy fuel, plugged cats...lots of things that can cause misfire individually or in concert with other problems.

    Did you run the codes yet?
    Thanks for the response. When we checked codes, there were none. Fuel was replaced. Cars been back on the road about once a week or so for about a month. It only seems to buck when shifting into third under acceleration. If you shift into third and baby the accelerator initially, you can then accelerate without issue. I sold the car to a friend about 4 years ago who kept it under roof, but didn't really drive it at all. I had the opportunity to buy her back and did - that's the reason for the 4 years of 'rest'.

  4. #4
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    Dec 2007
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    Salem OR
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    >When we checked codes, there were none.
    None? Not even 10 and 11?

    >It only seems to buck when shifting into third under acceleration.
    Unless you know the age/condition/gap of the plugs and wires, I'd start there. Still no joy, consider finishing the list I penciled above.

    Might be, tho, that all it needs is to see the boot on a clear stretch of road a few times

  5. #5
    Join Date
    May 2018
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    Irmo SC
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    166
    Did you ever find a solution I've been having some similar issues with mine just wondering if you found a cause

  6. #6
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    Nov 2012
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    Charleston, SC
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    Not yet - only because life has been crazy lately and it's not my daily driver. I know the plugs have some age on them so I plan to start with the plugs and wires... Keep me posted if you track down something first and I'll do the same.

    Thanks

  7. #7
    Join Date
    Apr 2002
    Location
    St. Charles, MO
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    21,155
    I agree that shuddering or bucking are most often an ignition problem caused by a bad spark plug or plug wire. Suggest replacing both.

    David
    1991 SC AOD 4.2..2.3 Whipple..........10.910 @ 125.61
    2016 SRT Challenger Hellcat.............10.597 @ 135.78

    My Garage

  8. #8
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    May 2018
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    Irmo SC
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    So I found the issue on mine not saying your having the same exact problem but might be worth checking so where the wire harness plugs into the ignition on the column near the key ignition its a large plug with multiple wires well my plug itself was broken so what was happening is that it would loose connection randomly and regain connection as if I where very quickly turning the key off/on so I replaced the plug and it hasn't done it since now I still feel some issues if I throttle pretty hard but I know that I have a minorly leaking head gasket so I'm assuming my left over issue is a compression problem but the other more recent issue was definitely the plug for the ignition

  9. #9
    Join Date
    Apr 2007
    Location
    New Orleans, LA
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    1,975
    ignition switch is a common failure item on our cars Ive probably replaced them on at least 5 of my supercoupes over the years.

  10. #10
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    May 2018
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    Irmo SC
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    Mine wasn't the ignition itself but the wire harness itself

  11. #11
    Join Date
    May 2018
    Location
    Irmo SC
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    166
    Well thought I fixed that issue but nope started doing it again backfired for no reason hard enough to blow something apart in my exhaust 3 years thousands of dollars can't drive the damn thing 2 miles and trust it just over it anyone know if a carborated 302 will bolt up to the m5r2? Just sick of dumping money into this pit

  12. #12
    Join Date
    Feb 2018
    Location
    Harrison OH
    Posts
    18
    Windsor motors and the 3.8s do have the same bell housing pattern. My 93 was originally 5.0 car and did the m5r2 swap on it. The accessory drive is the same as the 94-95 mustang (alternator bracket is different but the mustang bracket allows the use of the newer style and more powerful alternator). If you find a donor car the wiring harness should also be able to be swapped if you were still wanting to run fuel injection.
    93 5.0 (now a 363 stroker) LX Bill Elliott edition m5r2 swapped
    94 red SC 5 speed

  13. #13
    Join Date
    May 2018
    Location
    Irmo SC
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    166
    No gonna eventually go full carb

  14. #14
    Join Date
    May 2018
    Location
    Irmo SC
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    I've got a 78 f150 carb 302 that I'm gonna rebuild with some mild performance parts and drop it in but for now just trying to keep the 3.8 going guess I'm gonna do head gaskets and see what happens don't thing it's gonna fix my problem but I know it's a problem so

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