mikenavy

Ive got 4.10's with a tillman all out. I notice the bucking in first gear, when you're being unsteady on the throttle.. but that is just the nature of the vehicle. Although if I am consistent in acceleration on cold, warm, hot, cool startup w/e.. it doesn't buck.

you just need to be steady in accelerating. With 4.10's and a very responsive tune, at slow speed if you slightly vary the throttle it will buck....

cidsamuth

I'm being steady. Again, in the first few seconds of startup when cold, try accelerating slow and steady in first gear until the rpms pass 3500 or so. See if anything goofy happens at about 3000.

crescent_wrench

Mine has done this to some extent since day one. Maybe not all the way to 4500....hesitates at 3000....surges back at about 3500....cold or warm, doesn't matter. Only on partial throttle. WOT is no issue.

cidsamuth

Yea, you're describing the infamous 'flat spot' but I can't tell if you're experiencing the same surging/bucking issue that I am.

def67

Could it be because the idle is higher when the car is cold? My car has 355 and I dont have to give it any gas when its cold, just let the cluch out slowly and it will go, once its warm I have to give a little gas or it may stall.

Gene K

It's rubberbanding in the drivetrain. The steeper the rear axle and the more responsive the engine the worse the problem. Old carbed muscle cars do this to. I suspect the richer mixture during the warmup makes the problem worse.

EDIT: I read your later post and realized you were talking about something different. I believe you are complaining about the surge caused by the opening of the CMCVs. Their is no need to go above 2000 rpm until the temp gauge starts to move.

cidsamuth

Yea, if this is not a mechanical/sensor/tune problem, that is the only real explanation -- the opening of those plates at 3000 RPM causes a surge forward and then back, and the 4.10 gear makes it seem worse . . . causing a back and forth "bucking" motion.

However, my gut is that there is a problem, and the 4.10 is just making it seem worse. That's why I was hoping some others could try and replicate it. Even with the 3.31 or the 3.55, it would hiccup, even if it doesn't cause the more violent bucking that my 4.10 does.

Bieker

My 2007 GT did the same thing. I also thought there was a problem but now that I have a 2010 and it still does it. I doubt that both my cars had the exact same problem. The dealer never finds anything so I just ignore it. Either I shift before 3000 or give it a little more gas through 3000.

jocatch

My GT with 3.73 gears bucks badly when the car has been sitting outside in the cold, say below 40 for hours for example with the Brenspeed tune. Problem mostly goes away with the stock tune. Brenspeed says their tune makes the throttle open quicker making the cold engine response worst. Also, for the first minute or two a cold engine is running open loop until the cat converter "kicks in" so we should expect weird conditions when we start a cold engine. I even notice that my 5 speed manual is harder to shift when the temps are cold outside unitl it warms up.

Joe

cidsamuth

Joe, with your car, does it start surging and bucking when you approach 3000 RPM with a cold start? Again, it happens no other time for me.