Thanks, I was never sure what I had. But I knew it was an open diff. (Future mod.)

 

Mine does the same thing, Everytime I try to adjust for tire size it always turns back to default.

 

How do you know that? If you don't go to the screen that keeps all entered values, the next time you go to the gear screen it will be back to the default. We keep trying to tell you guys that. If you don't do the selection on saving settings, you have to start over everytime you go back to any selection for settings.

 

Sorry, I DON'T think that's your tire size! Those would be mighty "fat" tires. Is the middle number perhaps 75, or 65 or even 55?

And Eliminator, we're not trying to make life difficult here. We honestly want to help, so don't get your knickers in a twist.

If you tell me your REAL tire size, I can tell you what you should enter and I can just about guarantee it will be within 1% of the desired value.

IF you get your GR and TS riight, and if you don't "back out" of setting them before programming, your speedo will be correct.

IDIeselman - You are NOT going to the "Reload Previous Settings" option when you open the Custom Options menu.

- Jack

 

You may be on to someting Jack, but I thought the speedo was off to much to be just tires and assumed he had a typo and has 325/60/18s. Maybe I should not have.

 

Jim your right its 325/60/18 I know its supposed to be 2660 mm

So maybe someone can break it down step by step for me and then Ill go run it and see if the speedo is right.

I dont have my knickers in a knot I got flip flops on its CA haha

 

Ok, go into the settings and change shift pressure, any of the other stuff you want to, but when you get to the tires, enter 2600, not 2660. Then when you get to the gears, see if it says 3.73 and if it doesn't change it to 3.73. run the progam and then go drive. If it is still way off, then you need to check your gears manually. We witll get into that if it is still off.

 

Jim even thought the edge book says 2660 for that size of tire?

Im not gonna change any of the shift stuff cause i dont know much about it. So after im done changing all that stuff I just move up to done right and it should be good?

 

The numbers they have in the manual do not allow for the sidewall bulge with the weight of the truck(squish). I have allowed almost 3% for it. Now, keep in mind if you go back in to the custom settings area, youhave to do the Retain Values or whatever it's called before you go to any other screen, or they will be lost and you have to start over.

 

With a 60-series tire, I think Bluejay's 2600mm figure is probably about right. It COULD be smaller, but probably not less than 2575mm. The Edge values do not allow for the compression of the tire caused by the weight of your truck, which effectively reduces the rolling radius and the circumference.

Still, the number you entered (2660) would not give such a great error by itself. Please double check the door sticker on your truck to verify you have a "B6" axle and then make sure your GR is set at 3.73.

When you set your TS to 2600, make sure you hit [Enter] to "set" it and then do the same with GR. Then, scroll to "done" and hit [Enter] to start the programming with those values.

The next time you open the "Custom Options" menu, scroll immediately to "Load Previous Settings" and hit [Enter]. If you do anything before you "Load Previous Settings", you'll screw them up and will not get the former values you used.

- Jack

 

Thanks Jack and Jim for your help. I will drive it tomorrow and see how it does.

 

Well I drove it today to the dealership due to lower ball joints are going out to have them replaced. And I feel it is off atleast 10 mph still.

 

10 mph is a BIG error! However, you don't say whether the speedo is reading faster or slower than you're actually traveling. If it was like your earlier post, and the speedo is reading fast, then we need to know what speed you were at.

The dash speedo normally reads about 2-3 mph fast in the 70 mph range, because of mechanical errors - that's about a 3% error, which is just "the nature of the beast", and it might help keep you from getting a ticket. However, the other 7 mph error is caused by the PCM thinking you are traveling farther with each wheel revolution than you are actually doing.

If your GR is correct, the only other adjustment would be TS, which would need to be reduced. Try the 2575mm figure I gave you earlier.

And, how are you determining the "correct" speed? Is it with a GPS? Is someone with a radar gun tracking you? Don't rely on your senses, they are easily fooled.

I just don't see using a TS smaller than 2575mm though, unless your tires are badly under-inflated or your GR is wrong.

(Note - if you were actually moving faster than the speedo reading, you'd need to increase TS.)

Edit: Also read through the sticky I've just posted at the top of this forum on using the Custom Options feature.

- Jack

 

Jack thanks again for all the info. As far as the 10mph i think its off I think its two fast. And again its just my driving knowledge for alot of years and being a profesional driver that I base this off of. I might be incorrect I guess the best way to test it is to borrow someones gps or a radar gun to dtermine I wonder if while my truck is at the dealership if they can tell me if the speedo is off? I was also wondering if having a 6 inch lifts factors somewhere in the equation. Ill read through your sticky at the top of the page.

 

The 6 inch lift will make it "feel" like you are going slower than you are. I'd borrow a GPS.