Thread: How to Tune the MPG estimate in the DIC.

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  1. #1 How to Tune the MPG estimate in the DIC. 
    SE Level Member lightfoot__'s Avatar
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    I have heard that the dic uses the IFR table, so since mine was off 5-10% I added 5% to the ifr table and then fixed my maf table for fuel trims. My dic showed 26.7mpg I got 23mpg. It is not any closer. How do you tune the dic estimate to be right?

    (ps I search clubgp and pt forums and didn't find anything to help, at club gp someone asked and they just got reffered to pt forums, I went there, searched, nothing on the term "dic".)

    Can a mod change the heading to quesiton please?
    Last edited by DuBob; 01-17-2008 at 07:49 PM.
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  2. #2 Re: How to Tune the MPG estimate in the DIC. 
    GT Level Member DuBob's Avatar
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    Can a mod change the heading to quesiton please?
    Done

    Good question BTW, I've wondered this myself.
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  3. #3 Re: How to Tune the MPG estimate in the DIC. 
    I live here. SyntheticShield's Avatar
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    I recall Jerry or someone addressing this issue and I remember it being said that they had tuned it to where it was maybe a tenth or two off at worst. Now ask me where I saw that or where it was posted and I'll just stare off into yonder. I know that isnt much help other than to reinforce that it can be done.

    I thought Jerrys Tuning Notebook dealt with this, might want to check there.
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  4. #4 Re: How to Tune the MPG estimate in the DIC. 
    GTP Level Member Toasty's Avatar
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    Quote Originally Posted by SyntheticShield View Post
    I recall Jerry or someone addressing this issue and I remember it being said that they had tuned it to where it was maybe a tenth or two off at worst. Now ask me where I saw that or where it was posted and I'll just stare off into yonder. I know that isnt much help other than to reinforce that it can be done.

    I thought Jerrys Tuning Notebook dealt with this, might want to check there.

    yep, it's in the wiki


    - Make sure your IFR is the correct one for your car. This does 2 things. First is that
    your DIC indicated mileage indicated will be pretty accurate, and second is that it
    will be better able to meter the fuel out more accurately. Stock injectors = stock IFR.
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  5. #5 Re: How to Tune the MPG estimate in the DIC. 
    SS-DD Level Member IndeedSS's Avatar
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    If you want more infomation from Jerry, register at HPTuners as this is his new tuning forum hang out.
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  6. #6 Re: How to Tune the MPG estimate in the DIC. 
    Transmission Expert Trannyman95's Avatar
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    The fuel trims have to be as close to 0 as possible as if the pcm has to add or remove fuel in the fuel trims the result will show up on the DIC. Example.... if you added 42lb/hr injectors to a stock pcm tune then your DIC generally will tell you you are getting 36-39mpg on the highway. If you look at the LTFT while driving as it says this it will probably be in the -16.4 to -22 range so the pcm is pulling out a lot of fuel from its base fueling to compensate for the injectors, but unfortunately throws off everything when the trims are off that much. All the cars I have tuned with good fuel trims have pretty accurated DIC mpg readings and I found it best to reset the average right after a fillup at the gas station and AFTER you leave and reset it immediately while rolling down the road so it doesnt start at 0 from sitting still and have to work its way back up.
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  7. #7 Re: How to Tune the MPG estimate in the DIC. 
    SS-DD Level Member IndeedSS's Avatar
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    Quote Originally Posted by Trannyman95 View Post
    The fuel trims have to be as close to 0 as possible as if the pcm has to add or remove fuel in the fuel trims the result will show up on the DIC. Example.... if you added 42lb/hr injectors to a stock pcm tune then your DIC generally will tell you you are getting 36-39mpg on the highway. If you look at the LTFT while driving as it says this it will probably be in the -16.4 to -22 range so the pcm is pulling out a lot of fuel from its base fueling to compensate for the injectors, but unfortunately throws off everything when the trims are off that much. All the cars I have tuned with good fuel trims have pretty accurated DIC mpg readings and I found it best to reset the average right after a fillup at the gas station and AFTER you leave and reset it immediately while rolling down the road so it doesnt start at 0 from sitting still and have to work its way back up.
    Dave tuned mine and iirc actual mpg is within 1 mpg of the DIC reading.
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  8. #8 Re: How to Tune the MPG estimate in the DIC. 
    GXP Level Member Zef_66's Avatar
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    Check this link out:

    Linky...
    2001 GSE
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  9. #9 Re: How to Tune the MPG estimate in the DIC. 
    SS-DD Level Member IndeedSS's Avatar
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    Quote Originally Posted by Zef_66 View Post
    Check this link out:

    Linky...
    Zef, you have to be a PT owner to be able to access that site. I could copy and paste, but the secret handshake would be known to everyone, and I, the violator would be pursecuted for my remaiining days.
    Last edited by IndeedSS; 01-18-2008 at 10:21 AM. Reason: pre coffee typing errors
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  10. #10 Re: How to Tune the MPG estimate in the DIC. 
    GXP Level Member Zef_66's Avatar
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    Quote Originally Posted by IndeedSS View Post
    Zef, yiou have to be a PT owner to be able to access that site. I could copy and paste, but the secret handshke would be known to everyone, and I, the violator would be pursecuted for my remaiining days.
    I will quote it then. I don't have anything to fear...

    First, if you do tune VE using *idle only* make sure you watch IATs, as they will tend to rise as you just idle, and as they rise, your trims will be all over with a VE tune. You will wind up chasing your tail over and over.

    Second, as far as tuning the DIC for accuracy - I have done exactly what Eddie has, and I have also had great results. My DIC fuel used and mpg are both pretty much spot on now as I check them every time I fill up. You are absolutely right, though. If you don't fill up at the same station, let it click off due to the same pressure, etc, etc, etc, you will get different results. But, in my findings, the error introduced due to these factors is minimal. I had very consistently optimistic fuel used readouts from my DIC vs actual everytime I filled up it was off 7% +/- 0.5%. I think that if you use the same pump and just go "full blast" you can get within a tenth of a gallon or better, which, over 12-13 gallons isn't all that much.

    I'm no expert tuner, but if it were me in your shoes, I would do "the best I can" for the IFR and VE/MAF tables meaning I would calculate IFR using the accepted method (math, percentage) the best that you can figure, and use some maf and available tables to put them in to what you think *should* be right. Then, especially if you are concerned about your DIC accuracy, but also I think it would result in increased IFR accuracy, use the following method:

    1. Drive around. If you are pegging your trims in either direction, you may want to globally increase the maf or something just to bring them into a workable range.

    2. Once you are not pegging your trims, fill up at a station, reset your DIC, and drive your car *easy* for at least a half tank, and then fill up the same way at the same station (if possible, but not necessary). Mark how many % which way your fuel used reads vs actual fuel pumped.

    3. If you can afford the time and gas, you should repeat a couple times to average your % error (which should have reasonable deviation).

    4. If the % error is more than a couple %, or whatever you are comfortable having your DIC accuracy at, then change the IFR table by the % required. ie, If you were reading 10% LESS fuel used, then decrease your IFR, if you were reading 10% MORE fuel used, then increase your IFR, and so on.

    5. Repeat steps 2 and 3 to see if your accuracy has improved. Chances are it has improved linearly (this has been my experience). If it has not improved to your liking, repeat steps 2-5.

    Once you have completed those steps, you can move on to tuning your VE as normal, and then tuning your MAF as normal.

    The reasoning I have behind this method, is that the IFR is the buliding block for everything else, and the VE is the building block for the MAF. So you should tune them in order. I may be the only one (other than maybe Eddie, I think), but I think that tuning the IFR using the DIC is a pretty good way of knowing if your IFR is close for your injectors. This is because I have faith that the calculations used by the computer to derive fuel used rely heavily on the IFR and these calculations, I feel, are probably more accurate than some standard numbers that are used for the stock (non-individually-flow-tested) injectors IFR, and in turn, more accurate than the numbers calculated based off stock for upgraded/different injectors.

    I just reread your original post, and I wanted to clarify my position... I tend to think that the IFR can only be at one spot that is "right." Meaning, that no matter what it is when you start, if you get your DIC accurate, it will end at the same place. And I think that this same place is the "right" IFR for your injectors/car/etc. Basically, I'm saying that you are, in fact, tuning your IFR. This goes for your ve and maf tables too. No matter where they are when you start, if you tune your IFR using the DIC and tune the ve and maf properly, you will end up with the same IFR, ve, and maf tables every time you tune your car, no matter what those tables looked like when you started. The caveat here is that you probably can't affectively tune any of these 3 if your trims are pegged, hence step 1.

    So, just a disclaimer disclaimer... This post is nothing more than a combination of stuff that has worked for me, and some general theory of a novice tuner! I await being disproven, and I probably will be
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  11. #11 Re: How to Tune the MPG estimate in the DIC. 
    I live here. SyntheticShield's Avatar
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    Great stuff right there. This needs to be stickied or put in the How To Section.
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  12. #12 Re: How to Tune the MPG estimate in the DIC. 
    GXP Level Member Zef_66's Avatar
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    Or added to the how to tune wiki...
    2001 GSE
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  13. #13 Re: How to Tune the MPG estimate in the DIC. 
    I live here. SyntheticShield's Avatar
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    Quote Originally Posted by Zef_66 View Post
    Or added to the how to tune wiki...
    That too.
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