Thread: Tuning for fuel efficiency...

How does one tune for efficiency? I have yet to hook up my Powrtuner (keyspan is on the way), but I just got access to their forum. If anyone has any links, or guides, or helpful tips on how I would go about this I would much appreciate it.

I am a beginner in tuning, though I already understand a lot of the concepts. I learn quick so feel free to throw it at me and I'll go with the learning curve.

There is a lot that can go into tuning for mileage. I am not even halfway there to a good mileage tune. Even trans settings play into it.

But first things first. Get acquainted to the scanner. You need to know how to scan the car, do writes, make changes, etc. Read the .bin on your PCM and make changes like fan settings and whatnot figure out how everything works. And do some scans. Get everything setup the way you want it.

Now you can start working on your tune once you are comfortable with how everything works. First you want to tune the VE table. This is the heart of your tune. The more time you spend tweaking this, and the tighter it gets, the better tune you will have and thus the better mileage you can obtain. I won't go into how to do these tunes as there are writeup elsewhere better than I can provide.

Once you have a good VE tune, you can tune your MAF table. From my experience, I spend about 10x the amount of time working on my VE than I do my MAF. It seems the better I get my VE table, the easier it is to tune the MAF, so don't get discouraged.

With the VE and MAF tables tuned, most people will go onto WOT fueling. I don't worry so much about that as I don't often go WOT when using a mileage tune. I will scan it and make sure I don't have any KR when going WOT. If I do, I will make some quick overall changes to account for it. But spend most of the time concentrating on the rest of my tune.

Next I start working on my timing. I use Eddie's Tuner Thingy program for this. I do many, many scans, and tweak my timing as best as I can to get the most timing possible without knock. But I won't go over 45° at cruise. Right now I am running 89 octane and once I get some other things straight, I will be dropping to run 87 octane. Sure, WOT sucks ass, but its a mileage tune, right?

That is a general overview of what you are going to do. But there are other changes that I also make. I play with my shift points dropping them down a little at light throttles. Also, allow the TCC to lockup earlier at light throttle, but unlock earlier at heavy throttle. Reason for this is that you use more gas by letting the car "lug" than you do making it unlock and downshift. I also set the supercharger to not come in till 30% throttle. Leave PE stock, or somewhere in there. Change my cold start fueling because that seems to be a really rich area.

I am sitting at work right now, so it is hard to remember all the little things I play around with. But the more you play, the better you will understand what things do. Just make small changes, one at a time, so you can learn how everything works. For me, I drive an hour each way to work. So that is a perfect time to scan and make changes. If you have to drive a lot that you wouldn't normally do to get scans, you are probably going to waste more gas than you are going to save.

Zef, absolutely WONDERFUL information. Rep points you get from me on this one. I may even sticky, so if want to give any further details Im sure it would be helpful.

Very long post and I know it took time to get it all typed so thank you for taking the time to do so. Kudos to you my friend.

One thing to note on the VE tuning. It has been discovered that not all of our OSID's use the VE table for other calculations. HPTuners was supposed to have included these other tables in their latest release so you can see if your PCM is referencing the VE table or not.

fwiw Trannyman said my car was the only one he had seen that showed any improvement doing a VE tune.

If it's not making a difference I wouldn't waste the gas. Evidently you can back up the stock table before you begin and then zero out the VE table to see if it makes any difference.

Why am I not surprised, LOL

Originally Posted by IndeedSS

If it's not making a difference I wouldn't waste the gas. Evidently you can back up the stock table before you begin and then zero out the VE table to see if it makes any difference.

I noticed an extreme difference on my car. But my 97 tables are pretty basic and everything made a difference. But everything from economy to idle to performance to response got better for me with a VE tune.

But also realize that VE stands for volumetric efficiency. Meaning how efficient your car is at using the air and fuel it is supplied. As you change mods, you need to change this table to match. I did my VE tune from a stock table, with most of the mods shown below. So it was a big difference from stock. Others that are running with a different PCM or tune may not notice as much of a difference.

Wow. Thanks so much Zef for the info so far.

Originally Posted by Zef_66

With the VE and MAF tables tuned, most people will go onto WOT fueling. I don't worry so much about that as I don't often go WOT when using a mileage tune.

Can you tune your VE and MAF tables for mileage, then tune your WOT fueling separately so you still get max performance? Or does it have to be a performance tune vs a mileage tune?

Originally Posted by Zef_66

Next I start working on my timing. I use Eddie's Tuner Thingy program for this.

Is this a program I can download?

Originally Posted by Zef_66

That is a general overview of what you are going to do. But there are other changes that I also make. I play with my shift points dropping them down a little at light throttles. Also, allow the TCC to lockup earlier at light throttle, but unlock earlier at heavy throttle. Reason for this is that you use more gas by letting the car "lug" than you do making it unlock and downshift. I also set the supercharger to not come in till 30% throttle. Leave PE stock, or somewhere in there. Change my cold start fueling because that seems to be a really rich area.

I would like to change the cold start fueling too. One other thing I had in mind is changing my TCC lockup so it can come on at ~25MPH instead of ~30MPH. I drive on base a lot and most areas on base the speed limit is 25MPH so I get crappy mileage not being able to hit lockup.

Originally Posted by Zef_66

If you have to drive a lot that you wouldn't normally do to get scans, you are probably going to waste more gas than you are going to save.

I don't normally drive a whole lot during the week, but during the weekends I like to get the car out (even if I have to go out for no reason) to keep in in good shape from the relatively shorter trips and low speeds during the week. Plus some WOT runs on occasion to keep it as clean as possible between cleaner treatments.

Originally Posted by Sabrewings

Wow. Thanks so much Zef for the info so far.

Can you tune your VE and MAF tables for mileage, then tune your WOT fueling separately so you still get max performance? Or does it have to be a performance tune vs a mileage tune?

Your MAF and VE tables are just tuned to keep your fueling as consistent as possible under all condition. It doesn't matter if you are doing a mileage tune or performance tune, the you start out the same by doing the VE and MAF tune the same way.

Originally Posted by Sabrewings

Is this a program I can download?

Yes, it is a program that you can download once you get access to the PT forums. Once you get access, if you still can't find it, let me know and I can direct you. But that is really the name of the program.

Originally Posted by Sabrewings

I would like to change the cold start fueling too. One other thing I had in mind is changing my TCC lockup so it can come on at ~25MPH instead of ~30MPH. I drive on base a lot and most areas on base the speed limit is 25MPH so I get crappy mileage not being able to hit lockup.

I actually modeled my cold start fueling from Ron Vogel. On the other forum he posted his Open Loop AF vs RPM vs Air Mass table and I had saved it. Changing this helped a lot. And I have tweaked it some from there.

As for lockup, that is easily changed in a few seconds. One of the simple things you can do when you first get your tuner. And that is another reason why people don't like to share tunes. What works well for your driving style, your car, and your mods won't really work for my car, even if they are the same year or model.

Originally Posted by Zef_66

Your MAF and VE tables are just tuned to keep your fueling as consistent as possible under all condition. It doesn't matter if you are doing a mileage tune or performance tune, the you start out the same by doing the VE and MAF tune the same way.

Gotcha. So, the more accurate the VE and MAF tunes the more efficient the car is?

I loosely understand the fuel cells (without having actually seen the editting screen for it). I take it I would keep the fuel cells for cruising at stoi (even heard running it slightly lean at cruise but not enough to knock helps MPG) and use the fuel cell for a little more rich?

I guess if I'm not making any sense you can just say so and I'll go hide and read some more.

I'll look for that program.

Originally Posted by Sabrewings

Gotcha. So, the more accurate the VE and MAF tunes the more efficient the car is?

I loosely understand the fuel cells (without having actually seen the editting screen for it). I take it I would keep the fuel cells for cruising at stoi (even heard running it slightly lean at cruise but not enough to knock helps MPG) and use the fuel cell for a little more rich?

I guess if I'm not making any sense you can just say so and I'll go hide and read some more.

I'll look for that program.

The fuel cells are used at different types of driving. You are in fuel cell one on de-acceleration. Fuel cell two on light acceleration. Fuel cell three on heavy acceleration. And Fuel cell 0 a idle. Fuel cell 4 at cruise. At least I think that is right, pulling from memory.

So basically, the way I see it (and this might be totally wrong, but again, this is the way I understand it. So someone correct me if I am wrong, please) is that these fuel cells act like fueling tables that you can see or change. These fuel cell tables, along with the VE and MAF (that you can change) regulate the amount of fuel as you drive. So by changing the VE and MAF tables, you can get your fueling dialed in.

The way you can tell how far good or bad your tables are is by watching your fuel trims. The long term fuel trims are global changes to your fueling that are learned by your computer, over a longer period of time. The short term fuel trims are for the quick changes to your fueling, and are typically not learned by your PCM. So, as you drive, if you watch your LTFT, and they are very far away from 0, or fluctuate a lot, you need to do some tuning. The closer to 0 the LTFTs get, the less changes your PCM needs to make to keep your air fuel ratio correct. So...you go out, scan, and watch your LTFTs. Since you want them as close to 0 as possible (so your computer doesn't have to make large jumps in fueling to keep the AF ratio correct), we make changes to wither the VE or MAF tables, which ever one we are working on. When the trims are far off, and the computer has to make large changes, there are points where the fueling is not correct and you are burning more fuel than needed. While these spots are short because the computer is quick to correct, they add up and will lower your efficiency.

Wow, I hope that made sense.

Originally Posted by Zef_66

Wow, I hope that made sense.

It did, indeed. Zef, your help has been invaluable. I can't wait to get that adapter and start seeing what I can squeeze out of it. Early July I've got a 380 mile (one way) trip I'm taking, so it'll be good to see how I can tune my highway cruise.

Originally Posted by TDCRacing

http://www.grandprixforums.net/f65/t...html#post49560


Im not even going to say how many miles to the gallon im at now

Thanks for the info. Should be a good read.