2004z71 wrote:i did
i like it.
the main thing i like is telling the transmission how to downshift.... like: to drop to 1st gear, at 40mph, that way when i slow down to take a turn i can really LAUNCH out of it again.
Yeah you're doing something wrong, or the tuner is, or the truck is.
I have an 05 Silverado 4x4, xcab, 6.0 and 40k miles. Also have 285/70R17 M/Ts, MBRP exhaust and a CIA which have been on for over 2 years. Obviously it isn't a daily driver. Have averaged 12.3 MPG on the dash (before lift and tires 14.1 I think it was). Got the i3 Platinum about a month ago. With tire size correction only 13.4 MPG on the dash (attribute the decrease from before the lift and tires to the increased rolling resistance of the M/Ts). With the 87 tune get 14.3 MPG. I have not yet adjusted any individual parameters aside from tire size (I used overall diameter of 33" because I know the actual diameter of my tires to be 33.4", not 32.6ish like the commonly accepted diameter of 285s), bumping rev limiter by 200 RPM, and raising speed limiter to 150 (because why not). I know gains are actual as I have checked these numbers on the same exact drive to my cabin which is 128 miles each way (mix of highway, back roads, and off road all through mountains), same gas (87) from the same Shell , and I have definitely used less gas. Will say I felt zero performance gain without tire size calibration on the 87 tune (tried to see if it was a placebo) it actually was worse than stock. With tire size calibration feels way better than without mostly due to the trans strategy working better with proper final drive ratio calculation. From what I can see the 87 tune is all about power management not gain. Now the Diablo tune totally different story, it bumps up timing and the fuel to support the timing the hp gains were noticeable either way. With Diablo tune did get 15.7 for the first 1/4 tank until I started to beat on it then went down to 13.2 (attribute most of that initial gain to the fuel not the tune and loss to my right foot though). For this tune gas was 1/4 tank 87, mixed in 5 gal of VP C20 (110 octane) racing fuel, then filled the rest of the way with 93.
I may be able to help if you haven't called Diablo tech support to get you straight yet. I'm no pro tuner or any part of Diablo but I am a real life legit get paid 120k/yr to fix cars every day professional mechanic so I'm not just a keyboard warrior taking a Google based guess......Sounds like you don't have a tune problem, you have a problem with the final drive ratio calculation based on what I have read. Read your other posts too, they're really consistent with that theory. You sure the tuner is set to the right tire size? I ask because the p metric input is stupid and the touch screen sucks? If you're 1000% sure you set the tire size right, maybe the truck didn't take it. Do you have any aftermarket stereo or a trailer brake controller? That messes with the CAN bus (network for the computers in the truck) if so unplug them when you tune.
Also just for trouble shooting purposes the tire size parameter change by its self should reflect a positive change in fuel economy on your dash, taller tire travels a greater distance per revolution. With adjusting the tire size the fuel economy that is calculated on the dash as well as the mileage you get per tank based off the odometer are going to go up because the speedometer and odometer were incorrect before. If it is the same mpg shows after tire size calibration as before, your truck didn't take the tune at all. If it goes down any then the size you put in is wrong (probably due to the stupid format and the fact that the screen sucks) or the overall diameter isn't consistent with the diameter the tuner expected for the size (which going 33" fixes that). Really sounds like wrong tire size is programmed, it's unlikely that you could use 22 gallons in 200 actual miles, that's like 9.1ish MPG. You'd need to have a long term fuel trim at least +25% to achieve those type of results, in which case with no forced induction, your catalytic converters would likely have melted shut by now and you would probably have a check engine light on. Unless your truck is spending 1/3 of its run time at idle not moving, your odometer is most likely wrong.
I dropped from an average of 16.1 to about 14.7 with the 87 tune. Only thing I have changed is the tire diameter as I have a taller tire than stock and I have DOD off. For 2 years I got consistently 16.1 with the factory tune with DOD off and tire size change. I am probably going back to modified stock tune.
2 MPG loss sounds about what the DOD would be worth. I get about 11-12 around town and about 15 on the highway in my 2004 Silverado Z71. To be fair, that is about the same as I got prior to tuning. I have larger tires, jacked up suspension, and it is too old to have a 4 cylinder mode. I use a custom 91 octane tune with fuel trims and spark as much as the truck could stand so I can burn the tires if I feel in the mood.
