First post, hope I’m doing it right. Hahaha
I’ve attached both my current tune (Matthew’s TSP tune – 12-20-13) and what is purported to be a stock Pontiac G8GT tune (g8 gt tune). I’ve been comparing them to see what was changed. The revised tune (mail-order tune) was supplied by the shop where I bought the cam. I’m not unhappy with them or the tune at all, just want to fine-tune it to my liking.
First off, my car. I’ve got a 2008 G8GT. It’s got a CAI, 224/228 .581./.588 114LSA cam (plus all the stuff needed to make it work, like springs, pushrods, etc.), DOD delete kit, LT headers (1.75”), and no cats. Everything else is stock.
Secondly, my issues:
1) The car seems to want to push through the brakes. This may be just a by-product of having a cam and stock torque converter. But, when coming to a stop, I have to use 50% more brake pedal pressure to get the car to stop. And, I have to hold it harder to keep it stopped. The idle seems to be normal in terms of RPMs, but the car wants to move. When I sit in neutral or park, the idle is also at a normal level. But, if I shift into drive from neutral without holding the brakes, it lurches forward like I’m pressing the gas and accelerates to about 7mph.
2) There is a slight hesitation when the car is cold. If I’m sitting at stop, and press the gas (hard or soft), the car stumbles for a half second before surging forward. This seems to go away when the car warms up.
3) Common to these cars is a 2-3 shift flare. It was somewhat present before, but is wildly exacerbated now. It doesn’t happen every single time the car shifts from 2-3. It’s far more likely to happen at WOT and in manual mode, but even then, it doesn’t happen every single time (70% of the time, or so). (If I treat it like a manual transmission, and let off the throttle as it shifts, it doesn’t happen.)
4) When in manual mode, upshifts are great. Downshifting from 4-3 is fine, and downshifting from 2-1 is fine. But, when I shift from 3-2, the rear tires almost lock up it shifts so hard.
Lastly, things I’ve looked at when comparing the tunes:
1) It appears that the “Base Idle RPM, Target Idle Speed” was left the same up to 68*F, lowered a bit from 90*-133*, then raised 175rpm from 176*-306*. While I guess that this could be causing the “push”, I just don’t know. It sure “feels” like the RPMs are right, but that the engine is somehow getting more fuel/air at those low RPMs, causing me to hold back more power being sent through the transmission. But, I have no idea how to check for that. This may simply be “something I have to live with” since I have a stock torque converter.
2) I don’t even know where to begin looking for this problem. It’s slightly annoying, but since it seems to go away when the car is warmed up, it’s not overly burdensome.
3) I’ve looked through the transmission tables and parameters, but I simply don’t see anything obvious that was changed only to the 2-3 shifting parameters that would suddenly cause this. I’m thinking that it was already there, and the newfound power is making it worse. I’ve seen some rumors that people adjust shift RPMs slightly (up or down a hundred RPM) or pressures to alleviate the problem. But, I haven’t seen anything definitive, just “try this, it worked for me”.
4) Again, looking through the relevant tables, I see lots of changes. But, nothing special about the 3-2 downshift that seems odd. Or, rather, I don’t see anything done to that specific shift that wasn’t done to other shifts.
If y’all don’t mind taking a look and offering your opinions. As I said, this is all new to me. I’ve read quite a bit, and am still reading. I’m not opposed to trying things out to see if they work, but I’m just a tad scared of changing something that will hurt the trans/motor. Pretty sure it’s typical “first time tuner” syndrome.
Feel free to let me know if you see anything else in there that should/shouldn’t be changed.
Again, thanks so much!
(PS – if anyone has need for advice on suspension or brakes, please let me know. That’s my strength, having designed, built and raced a custom suspension and brake setup on my 2000 Trans Am that won the 08-09 state championship. – just to repay the favor, if I can!)
g8 gt tune.hpt
Matthew's TSP tune - 12-20-13.hpt