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Jerking/Shuddering still

This is a discussion on Jerking/Shuddering still within the General Help forums, part of the LSx Technical Help Section category; 01' m6 ws6 47,000 miles, Car idles rought--meaning shakes when at idle, and jerks while driving, you can feel it ...

  1. #1
    freshduckie
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    Jerking/Shuddering still

    01' m6 ws6 47,000 miles,

    Car idles rought--meaning shakes when at idle, and jerks while driving, you can feel it alot in the shifter.

    I am running out of options here, would a bad fuel pump cause this problem, or something to do with the coils? How do I test these? Fuel filter new, fuel injector cleaner used twice, unplugged MAF and it did not really idle much different and strangly enough set know code when I did that, think my plugs & wires are good--changed recently, had a buddy use a computer to look for codes-none recieved and he tested the wires which were good too, I tried looking for a vaccum leak but I spray on a bunch of hose on the top of engine but don't hear anything. I hate to take to a shop for a "I don't know response" and a still pay for a look at.

    Somebody help me through this, its really annoying to drive

  2. #2
    I went to Playboy Mansion FantaZGuy28's Avatar
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    04 GTO M6

    Any mods? I was thinkin vaccum or misfire but since you checked those so im not sure?

  3. #3
    sleepermullet
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    When my 3.4l V6 Firebird did that, the cat was broken up and sliding down the exhaust pipe. Give the cat a tap and see if you hear some rattles. I'm probably wrong but its worth a shot

  4. #4
    freshduckie
    Guest
    I will check the cat, my mods are a lid, k&n air filter not over oiled, disconnect skip shift, ws6 short throw shifter, removed one baffel from ram air, thats about it.

    It has backfired a few times,but not usually.

    Thanks

  5. #5
    BlackHawk T/A
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    Running lean or rich? Get the A/F checked maybe.

  6. #6
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    Dark Blue
    1998 Pontaic TA

    o2

  7. #7
    Member keliente's Avatar
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    99 Firebird Formula

    It sounds like a car that is running too lean. I would start by checking out what the 02 sensors are doing.

  8. #8
    Beast
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    It could be the fuel pump. Have a shop check the fuel pressure, it only takes 1 minute to hook it up. You should be running around 40 psi (I think...).

    My car was running much like yours, and when I had it checked it was only 18 psi... replaced the fuel pump, and she runs like a champ. OH, and it was not throwing a code either.

    Good luck!

    Mark

  9. #9
    freshduckie
    Guest
    Well with the O2 sensors and if its running lean or not that would throw a code right, or not? I can check this with a computer like they use at shops right? The fuel pump idea is something I did not consider, its nice to know it did not throw a code because it fits the bill so far. These replys are a big help.

    Thanks
    Doug

  10. #10
    freshduckie
    Guest
    HOw do you tell the fuel pump?

  11. #11
    freshduckie
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    test the fuel pump I meant

  12. #12
    Beast
    Guest
    Quote Originally Posted by freshduckie
    test the fuel pump I meant

    Run it down to the repair shop and they can hook a set of gauges onto the car. It's just a screw on connection on the fuel rail. It takes about 2 minutes for them to test it. When the car is running your fuel pressure should be around 40 psi... mine was 18 psi and I had just changed out the fuel filter, so I knew it wasn't just a clogged filter. They changed out the pump ($800 - yikes!!) and it runs like a champ now.

    If I was doing it over again I would save a little money I think by getting an aftermarket pump rather than the stock GM part. It would be cheaper and would probably be a higher quality piece also.

    Mark

  13. #13
    Pepe LePew
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    If it's the fuel pump, your engine will really fall on it's face while trying to accelerate...you just won't be able to build RPM at all. A weak pump shouldn't affect your idle though.

    If you can't find or hear a vac leak, you've probably either got an ignition issue or an injector problem. The most basic way to test the wires is pulling them one at a time while your car is idling to see if one of them has no effect on the idle shake. If you pull one that doesn't change the idle, then you've identified the cylinder with a problem...you can then inspect the coil, wire, and plug. The same procedure can be done with your injectors if you can't find an ignition problem. Just unplug one at a time to see what it does to your idle.

    Oh, and be careful with the ignition...wear insulated gloves.

  14. #14
    Member mikeaford's Avatar
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    Pewter
    01 Trans Am

    I have the same issue with surging - so your saying with the car running unplug a fuel injector from the motor to see what's happening with it? What safety precautions should I take and what exactly would I be looking for? Seems dangerous imo, but you guys have save me thousands by helping me in the past. Let me know if there's a site that tells me how to do this - or is this basic easy testing? Don't laugh if I misunderstood your last post - at least not to my face... Thanks.

  15. #15
    Veteran 0rion's Avatar
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    Are there any local f-body clubs around there? Maybe you could hook up with someone and have them do a log to get a better picture of what's going on with the car. Are your exhaust tips sooted up more than usual? Check your plug wires really good and make sure a boot isn't cracked or any are touching the manifold. I would also check your fuel pressure as was suggested. The gauges are cheap and it's very simple to do. Just hook them up to the end of your drivers side fuel rail. Stock LS1 pressure should be 55-60 psi.

  16. #16
    Member mikeaford's Avatar
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    Pewter
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    I've decided to take a day off one day and head up to Baltimore I've heard there's a shop up there that does excellent work and I think theyed find the issue faster than the dealer. The dealer is great but they do not like to work on Trans Am's guess the engine bay size turns them off.. At least this is a specialty shop where if they didn't enjoy it they wouldn't touch them.

  17. #17
    Veteran 0rion's Avatar
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    98 Formula
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    If it ends up being your fuel pump and you have it replaced I'll buy your old one to raid it for the sender.

  18. #18
    Junior Member 79JON's Avatar
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    Hey, I know you said you changed the plugs and wires but recheck the plugs and make sure one of them didnt break. I recently took my 98 TA to get the plugs changed and for some reason a couple days later the number 1 spark plug broke and it was vibrating and backfiring in idle and when I put it in drive. Just something to check

  19. #19
    Member mikeaford's Avatar
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    Unfortunately fuel pump was good with 50 psi at key in and 60 psi at ignition. I was told to swap the Throttle position sensor, Ill do this after double checking my plugs with the lift the plugs shouldn't take me anytime whatsoever to pull out. But my mother in laws boyfriend is a mechanic and said he has seen quite a few TPS's go bad causing eratic behavior such as surging - one more thing to rule out which I hear is pretty cheap to swap. I'll keep you posted.

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