285s - MPG dropped... Normal?

[98chevy2500SS]

Very helpful information! Just called my local dealer and said they don’t do speedo recalibrations, so a Black Bear tune is what I am going to do. I’ll probably get a new ECM from them, and keep my original one.

Or I might get a tuner and then I would be able to do both trucks for cheaper. Is a Black Bear tune better or would a $300 tuner do just as good?

 

[kennythewelder]

BB is more effective than a hand held tuner. The advantage to a hand help (flash tuner) is that you can reprogram your truck at any time. I have a Jet programmer for my truck. Its nice to be able to recal my speedo, it does live data code reading. I was dissapointed in the performance of the Jet programmer. Its ok but not near as good as BB, or any live tune. Also once you tune 1 truck, tue flash tuner is locked to that truck. You can only tune another truck by setting the first truck back to OE setting.

 

[98chevy2500SS]

BB is more effective than a hand held tuner. The advantage to a hand help (flash tuner) is that you can reprogram your truck at any time. I have a Jet programmer for my truck. Its nice to be able to recal my speedo, it does live data code reading. I was dissapointed in the performance of the Jet programmer. Its ok but not near as good as BB, or any live tune. Also once you tune 1 truck, tue flash tuner is locked to that truck. You can only tune another truck by setting the first truck back to OE setting.

Damn, that sucks, thought I could save some money. Oh well, thanks. I will probably send the computer in to BB soon and see what they can do about it.

 

[kennythewelder]

The biggest improvement in my tune is the way the trans shifts. It was a huge improvement. Not jerky just sharp. It will bark a second now and then. The Jet programmer is effective, but not as much as BB tune is. A custom tune is just does a better job. The flash tuners are more wide spread for everyone to use. A custom tune is just for your truck more or less.

 

[BNielsen]

285s are about an inch taller and will cover more distance per revolution of the tire. The Speedo & odometer will be about 3.8 % slower or behind.

See this "tire size comparison" site. Provides visual & numerical comparisons.
https://tiresize.com/comparison/

Calculate speed on the fly?
So basically, just multiply your indicated speed by 4% (round up 3.8 for easier math) to get a number to add to your speed.
50 mph x .04 = 2.0 ..... 50 + 2 = 52 mph
Been doing this for decades with my lifted Jeeps (an easy 10% calculation)

Same for your odometer. 250 miles is actually close to 260.
250 x .04 = 10.
250 + 10 = 260.

Eventually, you'll do it in your head without thinking too much about it.
60 mph? 6x4=24. Add 2.4 = 62.4 mph.
70 mph? 7x4=28. Add 2.8 = 72.8
80 mph? 8x4=32. 83.2

Screenshot from the site I listed above:

You must be registered for see images attach

Most all tire diameter & width increase will cost mileage. While it may lower rpms at a given speed, it requires more fuel to keep the extra weight rolling at the same speed.
..... The killer is the added wind resistance of the extra width (tire surface area) as well as increased area for air to go under the vehicle (very un-aero dynamic under there) causing more resistance.... requiring more throttle/fuel.

There's multiple force vectors at work in the physics of increased tire size.

So I guess I should factor in getting the mileage on my odometer corrected when I send a cluster out to be rebuilt? I never knew the difference in miles was that severe.
Then I need to get off my ass and get HP tuners and start compensating for power loss with tuning. I can't find a 4.10 gear set to save my life and I don't want to lose the 285s
------------------
I would also recommend the Black Bear tune, I bought a blemished computer and it showed up with like 7% of the paint still on it so I regret not paying for an unblemished ECM.
As much as the 0411 is worth it, I don't know that I'd ever do another one if I have to deal with all the problems again.

 

[df2x4]

X2 on what Kenny said. A real tune is going to be better than a handheld programmer every time.

 

[andy396]

As much as the 0411 is worth it, I don't know that I'd ever do another one if I have to deal with all the problems again.

Can you elaborate more on “the problems”?

 

[BNielsen]

Can you elaborate more on “the problems”?

Well I had a few issues with the tune itself, timing was way high and a couple other things, but I had an idling issue where the truck would die if I put it in gear, and it wouldn't want to run if it was idling and in gear.
The issue wound up being the ENG-1 fuse being blown so the MAF wasn't reading (Had a code for a MAF, CMP, and the CKP) and it put the truck into speed density mode and it ran like ****, so after @Mangonesailor came down and we trouble shot it we found a few loose wires, the blown fuse, and he dialed the tune in some.
I also had a few issues that stemmed from mistakes I made like I didn't properly connect the VSSB pins so my speedo didn't work and my ABS light stayed on, as well as a few mis-pinned wires.

My truck was down for almost two weeks I think trying to trouble shoot everything, and it took the work of both Mangone and @Christian Steffen to get my truck up and running. If I would've had HPTuners I'm sure that I could've had them walk me through the steps to getting it figured, but I'm still really grateful they helped me out.

 

[Mangonesailor]

Well I had a few issues with the tune itself, timing was way high and a couple other things, but I had an idling issue where the truck would die if I put it in gear, and it wouldn't want to run if it was idling and in gear.
The issue wound up being the ENG-1 fuse being blown so the MAF wasn't reading (Had a code for a MAF, CMP, and the CKP) and it put the truck into speed density mode and it ran like ****, so after @Mangonesailor came down and we trouble shot it we found a few loose wires, the blown fuse, and he dialed the tune in some.
I also had a few issues that stemmed from mistakes I made like I didn't properly connect the VSSB pins so my speedo didn't work and my ABS light stayed on, as well as a few mis-pinned wires.

My truck was down for almost two weeks I think trying to trouble shoot everything, and it took the work of both Mangone and @Christian Steffen to get my truck up and running. If I would've had HPTuners I'm sure that I could've had them walk me through the steps to getting it figured, but I'm still really grateful they helped me out.

I really could've saved some time by installing VNC on your computer. I could've just remotely played with your tune without having to download anything to my own computer (That's how I was looking at those cameras at my work while I was down there. It's free. I log into the computer at home and browse Reddit while at work sometimes).

 

[andy396]

@BNielson thank you. I completely understand and can sympathize with what you were feeling during that time. Having a friend loan me his HPTuners has helped immensely in troubleshooting all the issues I’ve had. I’m still thinking I want to do the PCM swap just to get tow/haul mode. Just not now. There’s still too many things above it on the list.