I have posed this problem to the board before with no luck so I'll try it again...Here it goes....

I have a 91 B2L with a T56 conversion. I was able to scan the setup with both datamaster and craig moates software with no issues whatsoever. I added 4.10s to the car ans shortly there after i noticed a huge change in my MPH shown to the ECM...meaning my speedo is taken care of by the SGI - 5 dakota digital box, it shows true and accurate no jumping no problems at all. The only problem is my MPH as observed by the ECM it goes to extremes 255 and will stay there for a bit, then to zero and then everything inbetween no pattern no nothing ive scanned some serious miles to make sure no patterns or weird things are going on. THings ive checked and or changed...Laptop, ECM, Chip both stock style and newly burned, with and without craig motes ecm adapter, 2 differnt aldl cables, replaced VSS, with and without SGI-5, changed calibrations on chip to adjust for diferent scaling...the works...If anyone has had similar troubles or has any idea on how to correct this please let me know

Thanx in advance
Chris

 

ok two thing could be wrong here. the reluctor wheel is falling off the output shaft. or you have a grounded short. judging by the symptoms id say ground short.or a fualty ecm.