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HELP ! Bucking and jerking when trying to maintain speed!

This is a discussion on HELP ! Bucking and jerking when trying to maintain speed! within the General Help forums, part of the LSx Technical Help Section category; When Im cruising at 70 ish mph cruise control on or off the car starts to buck lightly and jerk ...

  1. #1
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    HELP ! Bucking and jerking when trying to maintain speed!

    When Im cruising at 70 ish mph cruise control on or off the car starts to buck lightly and jerk and after a second or so it gradually gets worse and the car is jerking back and forth. It never gets severe but i always let off the throttle or give it some to make it go away.

    the car doesnt sound as mean and its not as loud. its lost some serious bark but fairly smooth still and feels underpowered somewhat.

    it did pop a code while doing it 2 weeks ago i did plug a scanner and got bank 1 lean o2 code.

    I checked wires and plugs are tight but i didnt pull them (didnt have time)

    mods when i bought the car lastsummer B&B muffler kooks Lts and catted Y. i added in september or so crane 1.82 roller rockers valve springs (918 i think) and new plugs.

    frustrated so much that i havent put the hres on even though the weather is nice and am debating selling it unless I can sort this out.

    any thoughts guesses etc are appreciated.

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    O U 8 1 2 Spaz's Avatar
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    auto or M6???

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    Sorry it's an m6. Happens every few days for the last few weeks. This morning on the way to work it happened as I got into 6th and settle at about 75 mph where I usually set the cruise. I felt the hesitation and then te jerking started. It feels like when you're crawling at 1mph in a parking lot in 3rd gear and you're holding the brakes to move so slowly and the firing of the cylinders is making the car jerk forward.

    I was thinking melted cat and maybe parts got into the muffler and that cause the sound to get weaker but the code was for the o2 before the cat drivers side. The service engine light did pop on 2 weeks ago when it was bucking in 4th doing like 35 mph but it turned off an hour later and hasn't popped on again.

    The car does have a tune as well from previous owner.

    Just trying to add anything that may help .. I notice throttle response is worse. If I stomp on it wot it will almost bog and lag for a split second and then Slowly rev up. Maybe it's in my head but I'm sure it revved faster before this all happened.

    I do have a idle video from before and the car sounds nothing like it do before. Well it does just nearly not as loud. I'll go back to thesame spot and record one today to see if it is noticeable on an iPhone video.

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    Now in Summit LT1 Flavor! Y2KArcticSS's Avatar
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    Fuel pump or filter. You are not getting enough fuel to go 75mph in 6th...had this happen 1 week before my pump went out, that's why those two items are my guess. You are definitely not getting enough fuel.


    Edit: read more into your post, and sounds almost more like bad cats... I had that problem too, which caused a similar effect
    Last edited by Y2KArcticSS; 04-11-2011 at 01:34 PM.

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    Spaz is My Mentor SMWS6TA's Avatar
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    did you just fill up with gas?

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    what RPM's are you at when it happens??? have you tried putting it in another gear at the same speed to see if it still bucks???

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    Now in Summit LT1 Flavor! Y2KArcticSS's Avatar
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    Quote Originally Posted by Spaz View Post
    what RPM's are you at when it happens??? have you tried putting it in another gear at the same speed to see if it still bucks???
    70-75 in 6th ~1700-1800 RPM, if he's got stock gears

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    Stock gears. Yes if I drop down to 5th and hold speed it will still do it. Then it stops and just keep varying rpm because I don't want it to happen again.

    My best guess on fuel pump is that surely at idle it would pump enough to not change the sound? And cruising in 6th at 70 is pretty fuel efficient I wouldn't think the pump is very stressed doing that. Correct me if I'm wrong I'm just speaking my mind.

    I do think it could be the cats. The car did pass emissions at the end of last summer but the tune could be off a little and I've been babying the car all winter for fuel mileage with gas prices so insane. Perhaps not getting the cats hot enough all winter killed em I don't know but it's a good suggestion. Problem is wouldn't it trigger an o2 behind the cat if theyve failed? Why would it trigger a lean o2 before the cat ?

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    Quote Originally Posted by SMWS6TA View Post
    did you just fill up with gas?
    I go through almost 2 tanks a week how much I've been driving lately (sigh at $80-90 a fillup) so I can't guess it would be a specific tank of gas. From today to the first time it happened 2 weeks ago I've probably filled up 4-6 times at a few different stations.

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    Member ls1wallen's Avatar
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    subcribed to see what others think. I have the same thing going on with the jerking. Does it stop when you give it more gas?

    my car is getting harder and harder to start. Im thinking my fuel pump is about to go

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    Mines doing that but it's due o2's not reading right. You can watch them and they are reading lean (open headers arent holding enough exhaust or heat by them long enough to read) but if I go into the pe table or wot it smooths out. Check for exhaust leaks around the o2's and if you have a scanner watch the o2 activity
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    Yeah if I push in the throttle it stops the jerking and sometimes will do it again if I try to hold a speed right after I stop it. Today i drove a few miles just accelerating to 75 or so then letting it slow down to 70 and repeated that so I didn't have to hold a speed.

    Fuel pump does make sense though. I have 108k miles now so it's now a low miler but not excessive either I guess. I hope it's that simple.

    One other thing I noticed is black soot like stuff all over my back bumper and panel between the lights. Like it's been running really rich or something. It's just a guess I'll admit I haven't washed the car since it first started just cuz I'm upset about the jerking so it coil be dirt.

    The only thing I can relate what it feels like is when my dual sync distributor failed on my c4 corvette. The distributor died an the car started bucking and jerking real bad before shutting itself off. Makes me wonder if it's something to do with the timing or a position sensor under the timing cover.

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    Mine smokes like a diesel lol. Not really but you can see it in the mirrors after dark through other cars headlights

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    Quote Originally Posted by 5abivt View Post
    Yeah if I push in the throttle it stops the jerking and sometimes will do it again if I try to hold a speed right after I stop it. Today i drove a few miles just accelerating to 75 or so then letting it slow down to 70 and repeated that so I didn't have to hold a speed.

    Fuel pump does make sense though. I have 108k miles now so it's now a low miler but not excessive either I guess. I hope it's that simple.

    One other thing I noticed is black soot like stuff all over my back bumper and panel between the lights. Like it's been running really rich or something. It's just a guess I'll admit I haven't washed the car since it first started just cuz I'm upset about the jerking so it coil be dirt.

    The only thing I can relate what it feels like is when my dual sync distributor failed on my c4 corvette. The distributor died an the car started bucking and jerking real bad before shutting itself off. Makes me wonder if it's something to do with the timing or a position sensor under the timing cover.
    what was the lean code? I would start on that side first and look for exhaust leaks. It sounds like you have a false lean condition which could be an exhaust leak or an air pump that isn't shutting off or something like that. The soot is what tells me that.

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    Quote Originally Posted by Johnstonj2005 View Post
    Mines doing that but it's due o2's not reading right. You can watch them and they are reading lean (open headers arent holding enough exhaust or heat by them long enough to read) but if I go into the pe table or wot it smooths out. Check for exhaust leaks around the o2's and if you have a scanner watch the o2 activity
    I had someone plug an obd scanner I think it was :

    P 0131 o/2 low voltage*
    Bank 1 sensor 1

    I don't know if there were more codes or not. What to do then? When the rockers were installed I'm side the Air tubes had to be loosened and removed to get to the vlalve covers. Could there be a Leak of air at the air tube? I have block off platesa I

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    look for leaks on the drivers side....how many miles are on the O2's? Usually when you see that soot it's either a false lean or a bad O2 or something like that.

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    Quote Originally Posted by 0rion View Post
    what was the lean code? I would start on that side first and look for exhaust leaks. It sounds like you have a false lean condition which could be an exhaust leak or an air pump that isn't shutting off or something like that. The soot is what tells me that.
    Right you are a stuck open air pump would definitely trigger a lean code! I'm going to dig up the blockoff plates I ordered and just install them shortly when my lil one goes to sleep. I dot think the pump is stuck on or the sel light would probably pop all the time but I did buy the plates may as well use em.
    Last edited by 5abivt; 04-11-2011 at 04:46 PM.

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    I'll get under and check for leaks. I've been lazy to jack up the car to look (it's raised all the way on the gc coilovers but the winter tires are smaller od than stock so it still sits too low to see anything) and was going to just check when I had to swap my rims but I think I need to just get it up tonight and have a look.

    No idea how old the headers and exhaust work is but from the previous owners posts I dug up it was all done within the last 2 yrs. O2s I don't know if they were originals or new when the lts went on.

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    yeah...start simple and easy first by checking for leaks. It could just be a bad O2 but I would say chances are it's something else. If you have a bunch of miles on those O2's and have the expendable cash it might be a good idea to replace those anyhow.

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    I do recall not too long ago banging the exhaust on a speed bump I totally didn't see. Wasn't much but I can imagine how a small crack can cause this.
    If it were a bad o2 would it not trip a light and stay on? I'm confused by the fact that I don't have a light on.

    O2s are heated right? Any ballpark figure on cost? I do get cost at the local GM but I don't want to spend it if it's probably not the problem .
    Last edited by 5abivt; 04-11-2011 at 05:15 PM.

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