LB7 DIC MPG

[2004LB7]

Anyone have any experience adjusting table B0781 in the LB7 tunes to make the MPG on the cluster more accurate? I have a friend of a relative that would like me to adjust the tune, which he says is off by about 20%, to see if I can make it more accurate.

I don't know if it is off 20% access the whole range, city or only highway. Didn't get too much information yet. Would it be safe to just bump all the numbers in B0781 up 20% as a start or is there a specific area I should focus on? Never played with this table as my LB7 didn't have that function on the DIC

 

[2004LB7]

Maybe I should make an Excel spreadsheet that compares the difference between the stock PW table and the modified one and spits out the percentage. Then plugs the percentages into the DIC MPG table. Wonder if that would at least bring it back to stock tune accuracy. Wouldn't account for fuel pressure changes but may be better than guessing

 

[Ron Nielson]

Does B0781 just affect the DIC MPG? nothing else? And what variables does it consider? Just trying to learn a little.

 

[660catman]

I’m not sure if the accuracy of the DIC changes with years. Last fall on an all highway 1400 mile trip my actual mpg was 26.7. The DIC was higher at just over 28 mpg. Not towing and 65 mph cruising speed. Flat terrain and temps around 50f. Truck is all stock with no tune.


2013 Sierra SLE 2500HD Crew Cab

 

[2004LB7]

Does B0781 just affect the DIC MPG? nothing else? And what variables does it consider? Just trying to learn a little.

I believe all it does is affect the display. Nothing else. When the PW is modified it throws the DIC further off then it was stock and this table was a means of bringing it back in line with stock or perhaps even better if one wanted to spend the time

 

[2004LB7]

I’m not sure if the accuracy of the DIC changes with years. Last fall on an all highway 1400 mile trip my actual mpg was 26.7. The DIC was higher at just over 28 mpg. Not towing and 65 mph cruising speed. Flat terrain and temps around 50f. Truck is all stock with no tune.


2013 Sierra SLE 2500HD Crew Cab

The method the DIC gets it's MPG reading or the calculation to obtain the MPG changed when GM went from the Delphi ecm to the Bosch. And possibly changed again with the Denso.

My understanding is the ECM in the Delphi ECMs did the math and calculated the MPD from the table. Then sent the information to the cluster. In the Bosch ECMs the MPG is calculated from the MM3 pids since the tune is torque based to MM3 vs the older ones using MM3 to torque. The latter years using the PIDs "should" be more accurate even when tuned then the Delphi method of look up tables

Oh, and 26.7 MPG ? Must be down hill both ways with a tail wind

 

[660catman]

The method the DIC gets it's MPG reading or the calculation to obtain the MPG changed when GM went from the Delphi ecm to the Bosch. And possibly changed again with the Denso.

My understanding is the ECM in the Delphi ECMs did the math and calculated the MPD from the table. Then sent the information to the cluster. In the Bosch ECMs the MPG is calculated from the MM3 pids since the tune is torque based to MM3 vs the older ones using MM3 to torque. The latter years using the PIDs "should" be more accurate even when tuned then the Delphi method of look up tables

Oh, and 26.7 MPG ? Must be down hill both ways with a tail wind

I forgot to mention that’s a Canadian gallon. US mpg would be around just over 21.


2013 Sierra SLE 2500HD Crew Cab

 

[DAVe3283]

I adjust that table on all my LB7 tunes. You can just adjust it 20% across the board, but doing it based on PW modification works better.

I made a spreadsheet a long time ago to do that for me. I'll try and find it after work and upload it.

Sent from my FlashScan V2 using Tapatalk

 

[2004LB7]

I forgot to mention that’s a Canadian gallon. US mpg would be around just over 21.


2013 Sierra SLE 2500HD Crew Cab

That makes much more sense

 

[2004LB7]

I adjust that table on all my LB7 tunes. You can just adjust it 20% across the board, but doing it based on PW modification works better.

I made a spreadsheet a long time ago to do that for me. I'll try and find it after work and upload it.

Sent from my FlashScan V2 using Tapatalk

That would be great. Otherwise I can wip one up pretty easy if needed

 

[2004LB7]

That would be great. Otherwise I can wip one up pretty easy if needed

I was half way through making a calculator and ran across, I believe your calculator. It ended up being what I was building. So I just abandoned mine and used yours. If he ever stops by I'll load it up and see how he likes it

 

[DAVe3283]

I couldn't find where I'd posted this publicly before, so here it is. Last modified in 2009, so probably could use some updates with what we've learned about tuning so far.

The concept is really simple, about the only thing that jumps to mind that could make this work better is factoring in the injector lag. But overall, this has always gotten the DIC MPG readings close for me with stock injectors, and I don't own any rigs with stock injectors anymore, so I leave the updates as an exercise for the reader.

 

[2004LB7]

Incase you can't find the calculators in the future. I've dumped them all here

Calculators

Is there a way to collect up all of the latest spreadsheets, calculators, and other tools from the various threads and maybe link them into one sticky or perhaps the tool tab at the top? Maybe when one makes a useful tool, one or more mods can review it and if it passes muster then adds it to...

www.duramaxdiesels.com

 

[LBZ]

I forgot to mention that’s a Canadian gallon. US mpg would be around just over 21.


2013 Sierra SLE 2500HD Crew Cab

I always use US MPG as I’m nowhere near old enough to remember Canadian mpg when people actively used it and the only place on this continent you’re gonna buy a gal of fuel is in the US so……lol!

Last time I hand calculated mine I was .5 mpg lower than the DIC. I can live with that. Changed some tuning a bit so I should do it again and see where I’m at. Interesting to see how that table affects the DIC.

 

[660catman]

I always use US MPG as I’m nowhere near old enough to remember Canadian mpg when people actively used it and the only place on this continent you’re gonna buy a gal of fuel is in the US so……lol!

Last time I hand calculated mine I was .5 mpg lower than the DIC. I can live with that. Changed some tuning a bit so I should do it again and see where I’m at. Interesting to see how that table affects the DIC.

I’m an old school Canadian who lives out in the country where’s the roads are a MILE apart. I convert litres divided by 4.54 to gallons. Distance travelled in kilometres times .625 to get MILES. This litres per 100 km BS just confuses people with this pucking metric system!!


2013 Sierra SLE 2500HD Crew Cab

 

[LBZ]

Sure. Just curious why you still use the 4.54? If you change your vehicle to mpg it’s going to use the US measurement anyways.

Liters per 100 means nothing if you don’t know exactly how many liters you have in the tank. Super dumb.

 

[660catman]

Sure. Just curious why you still use the 4.54? If you change your vehicle to mpg it’s going to use the US measurement anyways.

Liters per 100 means nothing if you don’t know exactly how many liters you have in the tank. Super dumb.

Nothing in the guage cluster changes other than the odometer or any DIC message so I don’t bother. It’s not like I calculate mpg each time. Truck is fairly new to me and I was just comparing what my Silverado 5.3 did on the same trip. That did 18 mpg or 14 US mpg at best.
In the old days MPG was good with a higher number. So when we went metric someone decided to confuse us more with litres per 100 kilometres where it’s fuel usage to go 100 kms. So a lower number is better!

A bit off topic but I posted to give you an idea of how far off actual and DIC mpg’s were in one situation.




2013 Sierra SLE 2500HD Crew Cab

 

[2004LB7]

update.... no update yet...

so, the friend of my relative reached out and said he would be traveling to California in a few weeks and would like the updated tune loaded up. but also mentioned that, on top of his DIC MPG being way off, his speedometer is also about 4-5% slower than actual, range calculation is almost double what he actually gets, and real MPG is about 33% optimistic.

I double checked the tune and I do have the correct tire size entered for what he's running. 285/75/R16. so I'm not sure how the speedo is off. unless perhaps the stepper motors are going bad, and the needle is not where it should be.

I have an idea for the range calculation. his tune has a 34 gallon tank. but maybe he only has the 26 gal. it's an 04 CCSB. refresh my memory. did all the short beds come with 26 gal, even the crew cabs?

he is also asking if there is any way to get the tune to make the previous MPG that he used to get before the new injectors and tune. he said with the same configuration as before less the lift pump and new injectors he got 21-22 MPG. I find it hard to believe with a nearly 33" tire. unless only highway that he was getting that consistently.

attached is the latest tune that I want to try on his truck. but being that I don't have an LB7 anymore I have no way of telling how it will perform until he's here. if anyone wants to look it over and give any pointers to improve the MPG. it's a milder tune that is not supposed to trash the stock transmission in a short order. so, a noticeable bump in power but nothing crazy.

 

[DAVe3283]

My 2003 CCSB had the 26 gal tank, which is probably why his range is way off.

It is totally possible the steppers are toast, but I have never had good luck using EFILive's calculator to get the correct pulses per mile based on tire size on my LB7. Have him reset a trip meter when he fills up before a major highway section, drive straight through to another gas station as far as he can get away with, then write down the indicated miles from the trip meter. Compare that with the distance Google says he went, and that will get your speedo really close. Even better if he has a standalone GPS and can reset the GPS and a trip meter on a highway (straight and level is best) then go 100+ miles straight, and write down the 2 numbers. That is how I calibrate mine, and it makes my speedo dead on.

An initial glance and the tune looks sane, but I'd get rid of the valley in the timing as he goes from light throttle to mid throttle.


You can also increase the timing all the way down to 0 fueling, as with very small shots of fuel and the injector lag, it won't really be that far advanced and won't rattle. This kind of curve has worked well for me:

 

[2004LB7]

What kinda numbers do you have in the cruising range? Basically the little "hump" in my timing table