Smarter than the ECM?

d-dog · January 21, 2005

I've got a 97 Z71 with the 5.7 and auto. It sure seems like the truck doesn't want to downshift when it would be optimum. When I'm climbing a hill, with or without a trailer, it seems to lug a bit, but doesn't downshift. My "test" as to if it should have been in a lower gear, is to hold the throttle still at a given speed, pull it down into a lower gear and see if that same throttle position slows, hold speed or adds speed. More often than not, I actually pick up speed in the lower gear without giving it more gas.

Is this a valid assumption - that the optimum gear is where the throttle position is reduced??? Living in Washington state, there's lots of mountain grades so it seems that I'm always trying to select a better gear, than letting the system do it for me.

Appreciate any comments.

budhayes3 · January 21, 2005

I agree...seems like I really have to "force" it to downshift under certain conditions. If I mash the pedal, it'll go, but if I accelerate lightly, it'll just kinda lug. With the right software, and someone who knows how to use it, that can be tuned out. I'm sure that the PCM looks at vehicle speed, throttle angle, calculated load, and a few other parameters before it will allow a downshift to happen.

jth7186 · January 21, 2005

Can't you just tap the brake pedal while accelerating in OD and that will bump it out of OD?

That works in mine when it lugs in OD at about 42-45 mph on grade...

redvett · January 21, 2005

Can't you just tap the brake pedal while accelerating in OD and that will bump it out of OD?

You can but it unlocks the converter lockup and if you do it for too long a periods will burnup the trans since there is no cooling in OD. You are better to just leave it in 3rd gear in the hill climbs.

Butch 02 Denali · January 21, 2005

Common problem. GM was getting complaints that the tranny was too busy(shifting up and down too much) so they "corrected" it by making the kickdown require more throttle pressure. I had Wester's reduce my downshift ease and now it's perfect. Any custom tuner that know what they are doing should be able to do this for you.

budhayes3 · January 22, 2005

I had Wester's reduce my downshift ease and now it's perfect. Any custom tuner that know what they are doing should be able to do this for you.

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Yea, I neglected to mention that I no longer have that issue either...should have been typing in past tense. Bryan at PCMforLess took care of mine.