Section for discussion of custom tunes?

Shdwdrgn

Original poster
Member
Dec 4, 2011
568
I've seen a number of members here are using HPTuners, and was wondering if there would be any interest in a new section dedicated to tuning our platforms? I know there's a bit of discussion on HPT's forum, but it seems like we might benefit from more specialized topics?

Some specific topics that hit close to home...
  • The ever-popular "I've changed my tire size, how do I adjust my speedometer?"
  • Techniques for dialing in fuel trims
  • I've been reading some articles suggesting that modifying the cam tables can help reduce the mpg drop-off above 65mph - anyone experimented in this area?
  • Any example tables for modifying shift firmness?
  • Discussions on complete system changes such as E-fans or modding for E85
  • Torque management -- when it should or should not be used
  • Changes to consider when tuning for a special application such as racing or towing

My HPT package is scheduled for delivery tomorrow, and I'm anxious to start pulling some scans to see how things are running now... but as I get more knowledgeable I would love to pick other member's brains for ideas on how to really get the most out of my investment.
 

Black LT

Member
Dec 4, 2011
211
Maybe this is that section! (just saying lets get it going here and if it shows that it's is worthy they may do it?)
I'll definately be reading it.
I have HPT but didn't have time to learn to use it yet.
Shift points is first on my list. I think there are a few things that change them. I like how my truck shifts when it's cold (I have PCMforless level 2, vette servo, .490 boost valve, and accumulator). Then after warm up, the shifts are softer. Is there a way to make the warm shifts harder without making the cold shifts even harder?
 

Shdwdrgn

Original poster
Member
Dec 4, 2011
568
I also have a PCMforLess tune, and they were kind enough to send me the stock and tuned files for my own comparison. Of course it wouldn't be right to just post their charts, but I've gotta say that even with having the changes right in front of me, I'm still having a lot of trouble understanding what changes the firmness. The tables I would expect to find differences in, there are none. It would be really great if someone with the knowledge were able to explain how this is accomplished.

On the other hand, some tables are pretty self-explanatory. For instance, the table that sets shifting by speed and throttle position... sure that makes sense. I have 3.42 gears, and am actually contemplating disabling the 3-4 shift at 40mph and below. My reasoning is that at these speeds (and my gear ratio) there is no reason to shift into overdrive, and the moment you give it a little extra gas it just downshifts anyway. Might as well save wear&tear on the tranny, if it still drives like I expect.

I was thinking about what you said on the shifts being firmer while the tranny is cold... Take a look under auto shift properties -> general -> force motor current. This seems to be the only table that is adjusted by temperature. I don't know what the 'safe' range of values are, but it seems that maybe if there was less of a drop-off down to the hot range, you might get a more consistent shift? Like I said, I have no idea how it all works, so don't make changes that are going to grenade your tranny! With that said, mine seems to be very consistent across the temperature range, so I would guess you need to compensate for the other upgrades you made (which are probably being affected by the cold differently than the stock parts).

The first thing I want to tackle when my kit arrives is the fuel trims. It appears the PCM can only compensate within a limited range, so getting the trims as close to zero as possible seems the best way to ensure peak performance and mileage. Then adjust for WOT to get the best performance, and we should be in business. I've seen various articles for this procedure, and will try to write up my own once I get it down. Then I can start playing around with transmission settings.
 

Shdwdrgn

Original poster
Member
Dec 4, 2011
568
So my kit arrived yesterday, and I promptly tested it by taking images of both my stock and pcm4less pcm's. Gotta keep those baselines handy! This morning I did a short scan with the default settings. I had a bit of trouble getting the histograms to show up because my engine doesn't have a MAF. Once I finally figured out to map against MAP/RPM, I got some useful data (useful meaning I have a lot of work to do...). That's when I realized that the main VE tables everyone talks about for adjusting your fuel trims...do not exist on our platform. Instead we have 5 different VE tables that nobody seems to fully understand. Apparently we have a lack of decent sensors in our engines, and GM made up for it by using a lot of convoluted tables to guess what the engine is doing at different times.

So far the best info I've been able to find is this... Tuning Multiple VE tables. Specifically around the middle of page 3 it seems like somebody is finally figuring out how to tune the multiple tables, but if there was an explanation in there, I totally missed it. Can anyone else translate? Or more importantly, this thread is from 2006 -- I don't suppose anyone has a more up-to-date procedure they'd like to share, and can break it down so us newbs can understand it?

From a short scan this morning (my laptop battery only lasted 15 minutes), my long-term and short-term fuel trims added together were swinging from -9 to +10. That seems to be way outside the ideal range, so I think this is one of the first things I need to try and figure out.

I also ran across some discussions that people were gaining 1-2mpg by adjusting their DFCO values (Engine; Fuel; Cutoff/DFCO), but I didn't see anything on HOW they were modifying the values.

Oh, and one more discovery... I know there was some chat at one time about the speed at which the throttle plate opens. I found info here on how to adjust that rate.
 

jbacklund

Member
Dec 16, 2012
118
Shdwdrgn said:
From a short scan this morning (my laptop battery only lasted 15 minutes), my long-term and short-term fuel trims added together were swinging from -9 to +10. That seems to be way outside the ideal range, so I think this is one of the first things I need to try and figure out.

So what's your long term fuel trim only? Mine is from -9 to -3. The STFT should just oscillate between +-5%. I'd say the LTFT is what's interesting in the end.

Did you log the fuel trim cell as well during your run? I think that would help out to find where to change the tune. If possible upload your scan.
 

jbacklund

Member
Dec 16, 2012
118
Just found this, might help with understanding fuel trim cell.

Fuel Cell Load condition Operating condition
0 Non-load Coast
1 Non-load Deceleration
2 Non-load Deceleration/Cruise
3 Non-load Deceleration/Cruise
4 Non-load Part throttle
5 Non-load Part throttle
6 Load Part throttle
7 Load Part throttle
8 Load Part throttle
9 Load Part throttle
10 Load Part throttle
11 Load Part throttle
12 Load Part throttle
13 Load Part throttle
14 Load Part throttle
15 WOT 100% load
16 Idle (Warm) A4 (P/N) A/C on
17 Idle (Warm) A4 (P/N) A/C off
18 Idle (Warm) In Gear A/C on
19 Idle (Warm) In Gear A/C off
20 Idle (Cold) All conditions
21 Non-load Moderate to high deceleration
22 WOT <100% load
 

Shdwdrgn

Original poster
Member
Dec 4, 2011
568
OK, one log file attached, and yes, it appears fuel trim cell was also logged. What does that one mean? I don't believe I've seen it mentioned before.

Keep in mind this is my first and only log so far. The PCM was reset from being disconnected, and this log begins just after cold-starting the truck. It sat idle for a couple minutes before I left, and of course took some time to warm up... Since the engine wasn't already up to operating temps, I'm not sure how useful this will be, other than as a learning tool, but hopefully next time I will know what I should be logging and get everything captured.

Also, I'm off to look at a cheap laptop from craigslist this morning. I found an old Sony Vaio that is small, but has nice resolution, and is decked out a lot better than what I'm using. And it has a battery that lasts more than 10 minutes! :thumbsup:
 

jbacklund

Member
Dec 16, 2012
118
The whole table with MAP vs RPM is divided into different fuel trim cells (1-15). That means the fuel trim can be different depending on what cells in the table you're running in.

In your log I can see the long term fuel trim wasn't learnt fully yet, but if you keep scanning you can see that the long term fuel trim will vary depending on MAP and RPM. When it does it will also switch fuel trim cell.

I'm not an expert at all when it comes to tuning, I've just been driving around and logging a lot of data to get an understanding on what's going on. So please correct me if I'm wrong.

In your log I also see that you have some knock retard. Was this on your stock tune?

BTW, you find the DFCO tab under "Fuel". When I've been scanning during deceleration my MAP is almost never been below 25 kPa which is the DFCO default for enabling it. So if setting it a little bit higher I guess that would help with the MPG. I saw your was down to 22 kPa.
 

Shdwdrgn

Original poster
Member
Dec 4, 2011
568
I'm still running the tune I got from PCMforLess, not the stock tune. Yeah it doesn't surprise me that the LTFT tables didn't get filled in during that brief period. Once I know what to log, I'll grab a new one.

Got the new laptop today. It has Chinese windows on it, so I'm in the process of wiping and reloading, but this battery looks to be good for an easy 2 hours, so I'll be able to get some much longer logs taken afterwards.
 

Shdwdrgn

Original poster
Member
Dec 4, 2011
568
I've spent most of the day making changes to my PCM, trying them out and seeing what I like. First off, the tranny changes...

To adjust shift firmness, go into Trans -> Auto shift properties -> General -> Force motor current. If you multiply the entire table by 0.90, you make it shift 10% firmer (lower numbers are harder shifts). I have no idea what the safety range is in this, but that 10% certainly feels better than stock!

The next thing is Trans -> Auto shift properties -> Shift time -> Normal. The stock values make for a really squishy shift. For my 1-2 shift, I entered 0.125 on the left and 0.050 on the right, then smoothed the values. For my 2-3 shift I used 0.075 on the left and 0.050 on the right, and again smoothed the values. The 3-4 shift is already all zeros, so I left it along. Again, I don't know what is considered a 'safe' range for these numbers, but this gave me a fairly smooth shift while in town, but kicks in harder when you hit the gas.

Most of my time has been spent going through all the combinations of changes for correcting the speedometer. There seems to be almost no information on this, other than it can't be done. Well I had a free day, so I went through quite a number of combinations, changing the four values we have available. My final solution seems to be changing only the drive sprocket ratio. My tires are 3.74% larger than stock (making my speedo off by about 3 @ 65mph), so I entered a ratio of 1.0374. As far as I can tell, the HPT gauges, my dash speedo, and my GPS all appeared to match at 65mph. Now I really don't know if this affects anything else, but it would be interesting if someone else could give this a try and see if they have similar results?

Oh yes, and of course my P0410 CEL is gone for good! :wootwoot: The dash looks so dark without it.
 

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