Some may remember a while back I was asking about the VSS and how it reports to the ecm and whatnot. I was pretty sure that when the speedometer in the car was recalibrated (stock it read to 85, it now reads twice that... or 170) that the ECM was not seeing the correct MPH anymore and was screwing up the torque converter lockup. BZZZZZZZZZZT! WRONG ANSWER! Turns out it was a gearshift swap (a story in itself), but most importantly, the recalibration of the speedo, which has what looks like an optical pickup for the VSS signal made NO difference in the MPH reported to the ECM. Dont ask me, I dont know... I dont know electronics or that setup well enough to even figure out whats going on there, nor do I want to expend the effort figuring out why. I do know it didnt care the speedo was recalibrated.

So a little rundown:
If you swap a TPI into a G-body, if its a MAF setup it will work just dandy with the stock VSS setup. If you go to SD, you get to change the signal via an aftermarket setup so the MPH reads right in the ECM, or there might be a possibility of a similar VSS that would report correctly available from another car... like a Camaro possibly.

 

Right, MAF is 2 pulse VSS, SD is 4. I am of course running the stock VSS setup in my 86 that has 86 LB9 injection.

Someone (who might read this) used a Dakota Digital signal changing box when he went w/ a T56 & 140 'Bird elec. speedo in his L98 G-body, but I forget the details.

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jmd
1986 SS with...
86LB9 TPI atop the original L69, Hooker emissions legal PN 2050 headers, stock L69 cat (yes, a real one), hydraulic clutch T5, Energizer 272 cam, chargedair.com fan, Global West CNR-88-C negative roll kit, 89 Iroc front springs, CC635 Moog rear springs and a whole bunch of other fun stuff

 

Why would you use a seperate box to calibrate the G-body speedo VSS to the SD ECM (730.)

pulse per mile constant, quick and free fix...

 

If I knew you could change that on the SD (probably heard it sometime, obviously didnt care ) I wouldnt have said that. There isnt a place in the MAF code tho, I looked. Dont need it anyway