4L80E Rear VSS Wiring

[pilotXC]

Originally Posted by dayj1

You probably know this, but there is a little math involved here. Get it wrong, and you get the symptoms that you describe. The sender that you linked is 8k ppm which is much lower resolution than you'd get with the stock 40 tooth reluctor wheel on a 4l80e output shaft (it'd be more along 100K ppm depending on exact gear ratio and tire size).

The factory ECM is going to want the number of pulses per driveshaft revolution. 20168 divided by your tire height (in inches) and then multiplied by your gear ratio (i.e. 3.08, 3.73, 4.11, etc) will give you the number of driveshaft revolutions in a mile for your vehicle.

Since you're generating 8k pulses with your aftermarket sensor in that same one mile distance, divide 8000 by the number of driveshaft revolutions you calculated to get pulses per revolution. It's going to be a lot less than the factory 40 in the tune (probably in the single digits).

That'll be the number you need in your tune and that's all assuming your speedo gears in the transfer case are correct for your gear ratio/tire size. If not, you'll need to adjust the calculations to account for that, too.

Thank you for the detailed post. The person who modified my harness has done a few of these 8k pulse generators and tuned it accordingly he has told me. My tires are 285/75/16, so 33" in diameter and gear ratio is 4.11. Doing the math, that gives me 3.184925 pulses per revolution...