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Thread: Tuning for optimal mpg with HP standard

  1. #1
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    Tuning for optimal mpg with HP standard

    Hey everyone I'm new to HP tuners I sold my DHP and got a IMO better platform. But anyways I had a custom tune on a PCM that a friend did for me. I noticed I was getting KR only during certain times ie going over a certain spot on the Verrazano bridge etc not when I'm on regular ground or anything. But I decided to put my PCM back to stock and I'm gonna go from there. My STFTs and LTFTs are not horrible but I think I may have a vacuum leak because LTFT is 16.4 constant at idle and 0 or close to it under acceleration and my mileage is basically 70% highway 30% street and still max 17-18mpg which for a pretty much stock car isn't great I feel cause people tend to get better mileage with the same model car. I'd like to know the best way to tune for this specifically what I should tune and how I should tune it? Thanks for the help my cars specs are...

    1997 Pontiac Grand Prix GTP (Supercharged 3800)
    Cold air intake
    3" catted down pipe to straight pipes
    10.3mm ZZP wires and AL 605 plugs

  2. #2
    Tuning Addict 5FDP's Avatar
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    Find the vacuum leak for sure.

    Clean the MAF sensor too, replace the upper o2 sensor if it's a old style denso as they are poor quality compared to new design.


    I never really did alot of fuel mileage tuning as these cars just eat gas in the city and only ever saw great mpgs on the freeway for longer periods. I normally only got 14-16 city but if I went up north to the cabin or something, getting 30-31 the whole trip was easy at 65-68 mph.

    I just really added timing for where the car would be during cruise spots, I also ran 93 octane fuel but thats doesnt matter a ton.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.

  3. #3
    Advanced Tuner CatnipG5Bandit's Avatar
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    My recipe for fuel mileage:

    1: trans pressures if automatic
    2: tune MAF/trims to the detail
    3: add as much timing as safely possible in cruise range. For me it was .16-.24g/cyl at 1400-2000rpm.

    4ish: I also changed stoich to 15. Yes, the O2 sensor corrects it but it still made a slight difference in my mpg, which was about 1mpg on my 4cyl car.
    5ish: I set the lower cells in the airflow switching (Fuel>OL/CL/>O2 rich/lean) to a lower voltage and it slowed down the excessive switching on my car.
    6ish: I also halved the closed loop proportional airflow vs mode. It made another 1 mpg.
    2008 Pontiac G5 2.2L (main oil seal became a crunchy Autumn leaf, RIP)
    2016 Fiesta 1.0L Ecoboost - Project "not-so-detestable"

  4. #4
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    5FDP I cleaned the MAF not long ago but I didn't no how to reset my fuel trims I thought it might have automatically done that when you wrote a file so I'm gonna do that in the am and log the car while I drive if it's still wonky on the LTFT I'm gonna try to find the vacuum leak.. I also don't know what o2 is in the car bank 1 or 2 the cars old I'd assume they were changed at some point but I will try those things first.. I might clean the MAF again just to cover all bases it's quick and easy.. Thanks

    CatnipG5Bandit I don't know how to go about tuning the MAF and trans I don't like messing with lol also how do I go about adjusting the timing? I'm not just asking for you guys to do it if you can point me in the direction where I can find the information out that would be awesome! I want to learn to fix my car and just in general learn "knowledge is power" as they say.. Thanks guys

    BTW I love this tuner wayyyy more then DHP far better interface, user friendly, scanner, support etc etc

  5. #5
    Advanced Tuner CatnipG5Bandit's Avatar
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    You can find how to tune your MAF by googling it. There are many threads throughout the internet. Also, here are a couple screenshots for resetting fuel trims and where your timing tables are.
    Attached Images Attached Images
    2008 Pontiac G5 2.2L (main oil seal became a crunchy Autumn leaf, RIP)
    2016 Fiesta 1.0L Ecoboost - Project "not-so-detestable"

  6. #6
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    Quote Originally Posted by CatnipG5Bandit View Post
    You can find how to tune your MAF by googling it. There are many threads throughout the internet. Also, here are a couple screenshots for resetting fuel trims and where your timing tables are.
    I found out how to reset them yesterday I wasn't aware there was a function for it on HP cause it's in the scanner as for DHP it's 1 program. I reset them and rewrote my old file the one with a little KR to see what my LTFT and STFTs were like. LTFT is at idle like +8 and STFT is bouncing around from +0-6 in a little I'm gonna put it back to stock and do a full write, reset the trims and clean the MAF and see where I'm at then if still high I will check for a vacuum leak.

  7. #7
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    OK so I cleaned the MAF, fully wrote the file, reset the fuel trims to both files I had and still when at idle it's pegged at 16.4 so yea I assume it's a vacuum leak I will have to test it one of these days

    BTW what I find strange is when I reset the trims LTFT stays pegged at 0 at times -0.6 and I drive for about 30 minutes and when I start the car back up later it's back to where it was.. Why's it stay for the drive but not after start up?

  8. #8
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    Quote Originally Posted by BRocedddd View Post
    Hey everyone I'm new to HP tuners I sold my DHP and got a IMO better platform. But anyways I had a custom tune on a PCM that a friend did for me. I noticed I was getting KR only during certain times ie going over a certain spot on the Verrazano bridge etc not when I'm on regular ground or anything. But I decided to put my PCM back to stock and I'm gonna go from there. My STFTs and LTFTs are not horrible but I think I may have a vacuum leak because LTFT is 16.4 constant at idle and 0 or close to it under acceleration and my mileage is basically 70% highway 30% street and still max 17-18mpg which for a pretty much stock car isn't great I feel cause people tend to get better mileage with the same model car. I'd like to know the best way to tune for this specifically what I should tune and how I should tune it? Thanks for the help my cars specs are...

    1997 Pontiac Grand Prix GTP (Supercharged 3800)
    Cold air intake
    3" catted down pipe to straight pipes
    10.3mm ZZP wires and AL 605 plugs
    get rid of those shitty zzp plug wires and get some stockers from autozone or napa or something.
    - 2001 Grand Prix XGT -- 11.57@122MPH
    - 2010 Chevy 2500HD LTZ -- Car hauler
    - 2011 BMW 328i Xdrive -- Wife's Daily
    - 2008 Ford F350 -- Under powered Pile O' Shit work truck

  9. #9
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    Quote Originally Posted by G_P_K View Post
    get rid of those shitty zzp plug wires and get some stockers from autozone or napa or something.
    I agree I'm gonna when I change the plugs next time I kept the wires because they were sold with the car to me and from what I know they aren't that bad just not special either

  10. #10
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    Quote Originally Posted by CatnipG5Bandit View Post
    My recipe for fuel mileage:

    1: trans pressures if automatic
    2: tune MAF/trims to the detail
    3: add as much timing as safely possible in cruise range. For me it was .16-.24g/cyl at 1400-2000rpm.

    4ish: I also changed stoich to 15. Yes, the O2 sensor corrects it but it still made a slight difference in my mpg, which was about 1mpg on my 4cyl car.
    5ish: I set the lower cells in the airflow switching (Fuel>OL/CL/>O2 rich/lean) to a lower voltage and it slowed down the excessive switching on my car.
    6ish: I also halved the closed loop proportional airflow vs mode. It made another 1 mpg.
    What exactly did you do to trans pressures?