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Trouble holding gears at wot

Practical Reflash Tuning

Discussion and questions related to the course Reflashing


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So the problem is that in my 2006 hummer h2 I can’t keep the vehicle in secound or third speed the gm 4 speed transmission ignores what I select and behaves like I’m driving in drive and shifts automatically ( down shifts / up shifts ) and mess up the datalog ... Anyone had similar problem? Is this some safety measure or something so you don’t mess up the transmission ? And if so how can it be disabled so you can hold gears at wot and if it’s not possible how can I go around this ?

That's a great question. I'm lucky as all the vehicles I tune are race cars with manual transmissions. But I am curious about how the best practices for running automatics on the dyno, or road testing at WOT.

Yes I remember the same problem with the older 4 speed autos. I used third gear but the trick is that you can't go to full throttle until you get past about 3000-3500 rpm or the transmission will kick down into 2nd. It's a bit of a pita but you can learn to work with it. Obviously this has an impact on your data below the point you can reach full throttle but generally you can get so close it's of little consequence. Watch your scanner and you'll get a feel for what max TPS you can hold and also what rpm you can transition to WOT. When you do go to WOT make sure you are smooth on the throttle to avoid any transient fuelling.

Thanks :)