1998 z71 stroker build

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

L31MaxExpress

I'm Awesome
Joined
Apr 21, 2018
Messages
5,890
Reaction score
7,539
Location
DFW, TX
Yes I think it’s that the tuner dude checked it while running and the ecm is reading oretty much same as gps. Maybe a mile or two an hr off but the speedo just keeps getting farther and farther off the faster it gets
VSS ratio has to be adjusted multiple places in a black box. Speedo has its own calibration parameters in th tune.
 

Rowdy Texan

Newbie
Joined
Jan 24, 2021
Messages
22
Reaction score
37
Location
Texas
Ok can you go in a bit more detail. I’m really unclear on all this I’m not sure what you mean by vss and black box
 

L31MaxExpress

I'm Awesome
Joined
Apr 21, 2018
Messages
5,890
Reaction score
7,539
Location
DFW, TX
Ok can you go in a bit more detail. I’m really unclear on all this I’m not sure what you mean by vss and black box

When I get a second, I will screenshot the HP Tuners speedo setup page and circle what I am talking about. Black box is the stock computer on these trucks. You are running one unless you did the 0411 PCM swap. 0411 is the silver PCM used in the 01-02 Express van.
 

L31MaxExpress

I'm Awesome
Joined
Apr 21, 2018
Messages
5,890
Reaction score
7,539
Location
DFW, TX
Back to what I was trying to explain yesterday. Most tires have a spec for how many revolutions make a mile. If not you can calculate the circumference from the diameter then divide 5,280 by the circumference to figure out how many revolutions they turn for a mile. The revolutions per mile needs to be multiplied by the rear gear ratio to get the number of transmission output shaft rotations per mile. That value needs to be loaded into the Trans/Revolution per mile constant. Then that value needs to be multiplied by 40 to get the number of VSS pulses per mile. The VSS reluctor is on the output shaft of the transmission and has 40 teeth. Once that is done the speedo should be close. If it is off a little can play with the VSS pulses per mile to fix it. Finally your ABS pulses per mile need to be rescaled by the same ratio you used for the trans revolution/mile. Take the old number that was stock in the computer and the new value and run them through a percentage difference calculator. Use that percentage to calculate the new abs-mile setting. If you fail to fix the ABS pulses for the new gears the ABS light will frequently illuminate and drive you crazy.

You must be registered for see images attach
 

Rowdy Texan

Newbie
Joined
Jan 24, 2021
Messages
22
Reaction score
37
Location
Texas
Back to what I was trying to explain yesterday. Most tires have a spec for how many revolutions make a mile. If not you can calculate the circumference from the diameter then divide 5,280 by the circumference to figure out how many revolutions they turn for a mile. The revolutions per mile needs to be multiplied by the rear gear ratio to get the number of transmission output shaft rotations per mile. That value needs to be loaded into the Trans/Revolution per mile constant. Then that value needs to be multiplied by 40 to get the number of VSS pulses per mile. The VSS reluctor is on the output shaft of the transmission and has 40 teeth. Once that is done the speedo should be close. If it is off a little can play with the VSS pulses per mile to fix it. Finally your ABS pulses per mile need to be rescaled by the same ratio you used for the trans revolution/mile. Take the old number that was stock in the computer and the new value and run them through a percentage difference calculator. Use that percentage to calculate the new abs-mile setting. If you fail to fix the ABS pulses for the new gears the ABS light will frequently illuminate and drive you crazy.

You must be registered for see images attach
Wow that’s really good info I’m gonna try this and hope it works. Thank you so much no one else has had any credible solutions they just say to change the gear ratio and tire size in hp tuners but that made it not wanna shift out of first gear the last time we tried that. I’ll try this out. Thanks is a million
 
Top