Lift/Tire opinion for a '08 6.4

[polarbear]

Before I go off half-cocked, here's the question. Member wants to put a 6" Pro-comp lift with 37's underneath a '08 F250 Crew 4X4 with a 6.4 PSD. In the land of Chebbie, the new '08's don't take kindly to these kind of mods. The primary issue is taking the ECM(s) outside of the factory parameters. Curent problems include

1) terrible fuel mileage. Dropped from the 13's into the 9's.
2) Regen seems to be hyperactive, injectors running rich (see #1)
3) Every time we try to re-flash for one issue, something new pops up. Since the truck is a LTZ mdel, all the memory functions get wiped out every time we try to do anything with the ECM.

My memory on Ford's is also that the front suspension, which wanders a bit on a good day anyways

 

[bowtiehatr]

the pcm and abs module may not communicated properly with the tire size, or there may just be another issue causing the regen. i dont see the lift having any cause for the regen unless the bigger tires caught a harness and unplugged something.

 

[blackhat620]

Ernie,

It is not the lift it is the larger tire diameter. Anytime the tire diameter is changed from OEM (larger or smaller) the VSS signal must be recalibrated.

On the Ford the VSS is derived from a tone ring mounted on the ring gear in the rear axle. So if you change the tire diameter you must recalibrate the PCM for the larger tire diameter (Revolution per mile). I know the Ford system was limited to IIRC 35" max tire diameter (601 Rev/mile) using the programmed abilities in the OEM PCM software. For the guys running larger tires than this, they install a "Truspeed" inline with the VSS signal to correct the input before it enters the PCM.

If the VSS signal is not correct for the actual tire size then inputs to the PCM will be incorrect and so the engine fueling and performance adjustments made by the PCM will be incorrect (this will effect fuel mileage and regen). Also the ABS will not work correctly because of faultiy VSS data.

I suspect you are experiencing the same problems with the Chevy. I do not know how the Chevy is getting its VSS signal (ie tone ring or gear at the transmission). Either way however you must recalibrate the VSS signal for the current tire diameter or the PCM will never work properly. I would have your tech call the GM hotline and ask them how to recalibrate the PCM for tire diameter and the max limit available. Also call and talk to Superlift about the "Truspeed"

www.superlift.com/accessories/truspeed.asp