Pontiac G8GT - idle/push, shifting problems

[00 Trans Ram]

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

[04blackgmc]

I have tuned some G8s with stock converter and a cam. I pulled the tune and there is some things i'd change on the motor side and trans side for sure.

Have you done any MAF tuning or wideband tuning or driveablity with the STFTs?

[00 Trans Ram]

I haven't done anything yet. I'm just learning about STFTs (and LTFTs), and don't have a wideband, but general drivability is pretty good. Running down the road, cruising, partial and WOT are all pretty spot on. Not saying that there isn't more to be had, but just based on accel numbers (used 1/4 timer app before mods and arrived at 292rwhp, or the advertised 361bhp; then used same app in similar conditions after mods and got 409rwhp, which is 505bhp), I think that most of the "running" parameters are good.

[HartRod]

I have an LS3/6L80 (stock converter) that I changed the cam in (219/235 113 LSA) and have a similar problem with the pushing. Everything that I have read and most of the people I have talked to, tends to point towards a higher stall. I'm currently looking at a 2800 single disc from Circle D. Did you change injectors? Also, you should try to do a 15-20 min log to go along with your tune. Then you can point out some of your problems in real time. I can't look at your tune right now, but will when I get home.

[00 Trans Ram]

I'll try to get a log if that helps.

Yeah, I was told that a slightly higher stall would solve the problem. It may come to that. But, I'd like to exhaust all other options before shelling out more $. (Or, in the case of a stall, $$$!)

[04blackgmc]

Yea a stall would get rid of that but you can get it pretty good on a stock with enough time and working at it.

[00 Trans Ram]

Yea a stall would get rid of that but you can get it pretty good on a stock with enough time and working at it.

So, what parameters should I begin adjusting? I think the first things I should try to alleviate are the shift flare and the hard 3-2 shift. Do I adjust shift pressures, shift times, or some other, more esoteric, parameter?

[04blackgmc]

So, what parameters should I begin adjusting? I think the first things I should try to alleviate are the shift flare and the hard 3-2 shift. Do I adjust shift pressures, shift times, or some other, more esoteric, parameter?

I sent you a private message.

Idle needs to be lowered since its on the stock stall. Hot idle needs to be around 700 or very close to it.
You'll need to mess with timing/timing drop/timing adder/idle air flow and some other things to get it dialed in.

I tuned a 227/243 it was either a 113 or 114 in a stock stall G8 it didn't drive like stock and pushed on the brakes a little but it was not bad considering the size of the cam lol.

[HartRod]

So, what parameters should I begin adjusting? I think the first things I should try to alleviate are the shift flare and the hard 3-2 shift. Do I adjust shift pressures, shift times, or some other, more esoteric, parameter?

I would be interested in this also. I can email you my tune so I don't clog Trans Rams thread.

[00 Trans Ram]

I would be interested in this also. I can email you my tune so I don't clog Trans Rams thread.

Hey, feel free to clog. Clog away! The more the merrier!!

[00 Trans Ram]

I sent you a private message.

Idle needs to be lowered since its on the stock stall. Hot idle needs to be around 700 or very close to it.
You'll need to mess with timing/timing drop/timing adder/idle air flow and some other things to get it dialed in.

I tuned a 227/243 it was either a 113 or 114 in a stock stall G8 it didn't drive like stock and pushed on the brakes a little but it was not bad considering the size of the cam lol.

Cool - I think I'll start out with this:

1) Adjust the idle settings
2) Modify the "Final Idle Airflow Minimum vs. RPM vs. Gear".

Here is my compare of the current tune vs stock (note that these values are what was INCREASED over the stock values):



I'm guessing that if I decrease these numbers a bit, then it'll help. This seems like exactly what I need. One thing that I've noticed is that when I'm rolling along, and let off the gas, the car continues accelerating (or, more accurately, not slowing down due to engine braking) for a half-second. And, if I shift to neutral while rolling, the idle slowly creeps up to about 2000rpm. As soon as I hit 0mph, the idle falls to 900 or so.

From reading the help menu in HP Tuners, I think this parameter controls this characteristic.

[04blackgmc]

Yea fine tuning idle air and timing will tame the sound and feel of the cam and can also make a smaller cam sound bigger and crazier than it really is.

Adjust the idle from 154* on to 700 and also the idle speed min table to 700 and start working on the idle air flow and timing to get it working better.

[HartRod]

Hey, feel free to clog. Clog away! The more the merrier!!

Thanks! Here you go.

[bluegoat06]

OP, your tune need lots of work, I wish things were as simple as adding 1.5% to the entire MAF table to tune a car with full exhaust and cam, LOL, What you have is a typical PE rape job, your trans is barely tuned, they removed some time from the shift, but left stock shift pressures, and removed ALL TM. i bet the WOT shift is not even consistent, how could it be with the way the shift MPH is tooned.

Start by adding your trans TM back, also visit the G8board tuning section, I've put lots of info for people like you starting to tune their G8's with HPT, all you need to do is read and get to work

[00 Trans Ram]

Thanks to everyone that posted help suggestions or pointed me in a direction to get help. I've attached a few files. My current tune is in the OP. Here is what I've changed - if someone can take a look through it before I flash the ECM tonight to make sure I haven't screwed something up royally, I'd appreciate it. Also attached are 2 log files - one is from cold start, through warm up, all at low speeds. Then, I have another which is of the car already warmed up, with a WOT, high-speed run.

In the next post, I'm going to summarize what I changed in the tune to arrive at what I'll install tonight.

Matthew's test tune from G8Board and HPTuners suggestions - 12-26-13.hpt

Cold start, low-speed - 12-27-13.hpl

Warm start, WOT run - 12-27-13.hpl

[00 Trans Ram]

Here is what I've changed. Things with a red "X" in front are things that I've changed. I did not make a few of the changes (Idle Proportional Airflow, Idle Integral Airflow, Baro Multiplier, and things without notes next to them) because I didn't have enough information to know what I needed to change. The notes are what I've compiled from posters such as 04blackgmc, bluegoat06 and PatG (along with a few others).

I attached the Word file, as it contains screenshots of people's tunes, tables, colors, etc. Just easier to open the file than recreate in the post.

Changes to make to tune - 12-26-13.doc

[00 Trans Ram]

Well, I put the new tune on, and it helped some things, but hurt others.

I seem to have gotten rid of the 2-3 shift flare greatly, and also to have alleviated the push I'm feeling on the brakes. But, now all of my shifts fell kind of odd. When the gear releases, the RPMs drop as normal, but for a split second just before the new gear engages, there is a slight jolt as the car feels like I've tapped the brakes. Then the new gear comes on and it goes forward. When I log the run, I can actually see my RPMs drop below where the new gear comes in for a split second, and I drop 1-2 mph. It almost feels like the transmission is trying to hold the lower gear for a split second as the new gear engages, or something. I can't see anything in the log other than the symptoms, not the problem, though.

Also, my idle RPMs are much higher now. When I am going down the road, if I shift into N while moving, the RPMs creep up to 2000rpm and stay there, until I come to a complete stop, when they go back down to normal. Also, as I'm decelerating and stay in gear, the RPMs drop to alarmingly low levels, and the car almost stalls. They drop to 500rpm or even a little below.

Log files posted.

first drive after tune, WOT high speed.hpl

first drive after tune.hpl