Diablosport Forums

1. U7185
2. 2.02
3. 2005 GMC Sierra 2500HD CrewCab (LLY Duramax 6.6)

ISSUE #1 (Tire Size Adjustment needs adjusting)
I first wanted to correct my tires because I have upgraded from the stock 245 tire to the Goodyear 285/75/16 and I read about 2-3mph slower on my speedo then what my GPS reads.

So I tried all the suggestions found on this forum: 285/69/16, 265/75/16, 265/69/16, 245/75/16 and guess what? They all read the exact same 2mph slower on my speedo... so something just ain't right.

I modify tune (factory tune) and modify tire size. Wierd because it makes me enter the numers twice before it takes it. Then I install that tune that I adjusted and the exact same results.

ISSUE #2 (Burning fuel is not an option)
I figured I would try the HI-Tune (85HP) mode seeing how everyone states that gives them the best fuel economy. Holy Smoke Batman! Even at an idle I was puff the magic dragon and when I accelerated, even slowly, I looked like train running coal as fuel, pure black smoke.

I figured HI-TUNE wasn't for me, so I moved on down to the (65HP), of course modifying the tire size to one of the options I mentioned previously and still SMOKIN and still speedo issue. Of course, not near the smoke I had before.

My next stop will be the 40HP (Tow Tune) to see if that eliminates the smoke but before I do that, any ideas on the tire size thing. Why is it that every modification I make, my speedo is ALWAYS 2mph less then what the GPS says?

When it asks you to enter the tire size 2x, it is asking for the STOCK size first then the new size second so it can compare them.

Not sure on the smoke, sounds like your truck is not burning all of the fuel being commanded, but the tunes should not smoke excessively.

Thanks Mike..

Let me try the tire adjustment again by entering the stock first and those tries mentioned above again (Explains why it never changed).

I also submitted an RMA to take advantage of your newer programmers... bummer I loose the EGR option but I don't use it now anyhow.

I wonder if by messing with the different settings I have some build up on my injectors causing the smoke. Also is it possible the fueling station I'm getting my diesel could be giving me something more rotten smelling then the diesel fuel iteself? Reason I ask is because at the pump at a Marathon station there was a bunch of oil around the pump, like its been leaking but I figured at .20 less a gallon then anywhere else, its worth a shot.

Yes, it is very possible that you are getting not so great fuel, try a different station.

Just tested the correct way of adjusting tires and like magic it works. For the Goodyear 285/75/16 the first one I tried 285/69/16 worked like a charm. Checked at 0-60 and matches exact the whole way.

After having it on the STD-65hp tune, I just got on it a few times and it seemed to clear her throat and now she's not blowing black smoke nearly as much. Also put some Diesel Kleen in the tank to help get her regular again. I heard its like Ex-Lax for Diesel's... We'll see.

Thanks Again Mike

Awesome, good to hear.