GEM Swap Problem 1998 XLT 4wd

[Thaley615]

Experienced problem with intermittent dome light and 4x4 actuator functioning. Trouble shooting led me to GEM. Got used one on eBay, disconnected battery, installed. Problem seemingly resolved but, on test drive. When auto trans shifts to 2 new gear, stalls and speedo says I am going 70-100 mph? If I shift the selector to low (1) 2wd, sputters but does not stall when his 5 mph and shifts to second...idles for 15 min after install and then sputtered around neighborhood for 30 min as a post said it would re-set itself after a while...bad GEM?....suggestions?

 

[RonD]

I assume you don't have 4WABS(4 wheel ABS), if that is the case then yes GEM is used to set "true speed"
GEM gets VSS(vehicle speed sensor) signal from rear axle ABS sensor.
It then converts that signal to "true speed" using pre-programmed tire size, and sends that out to Computer(for shifting), speedometer for correct speed, and cruise.

It reads like the GEM you got is either bad or from a vehicle with 4WABS.
4WABS vehicles used the ABS module to correct for "True speed" so GEM was not programmed for it

If speedometer was just off a little then then I would think it was OK just needed correct tire size added, but you describe wild swings in speedometer so either GEM has no programming for this or it is bad