nater36

My autotap data logger is showing a different speed than my speedometer. 96 firebird formula. What would cause this?

Ed Wright

iTrader: (1)

The internal MPH is used by the PCM for shifts, EGR, EVAP, etc. the speedo is an output. Two different "scalers" there, you can adjust each one individually. Factory calibrations seldom agree there. When I dyno tuned one I normally dialed them both in to my dyno speedo. Made myself a list of popular gear/tire combos to use. Makes no difference if the internal value agrees, except for **** customers. LOL Amazing how many thought the speedo must be the one wrong if they don't agree. :-)
Not sure where that thinking come from. Scan tool is right, speedo must be wrong. LOL

nater36

I just never noticed it before. Speedo is correct. I kept getting a p0336 code so I changed the distributor and it is still there. High idle at 0mph and running extremely lean wot.

Ed Wright

iTrader: (1)

P0336 has nothing to do with the distributor. That is related to the crank position sensor in the timing cover.

ThoR294

iTrader: (6)

Speedos are wrong? no way! Closest I see to actual speed are speed traps, and various GPS units