mph differences
TECH Senior Member
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Joined: Oct 2006
Posts: 7,564
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From: Decatur, TN (N-W of Athens)
Is the Speedo controlled by the ECM or the VSS? If the signal passes through the ECM unchanged, then into the speedo, it might be reading it correctly, where as if the ECM has been tuned, it isn't. Why, I don't know, but again I'm just tossing out theories. I have a 4L60 in mine, so I don't have to worry about that BS lol
the speedo is controlled by the computer. so i don't see how the controlling unit could be off and what it is sending a signal to could be right? everything was working fine for the last few hundred miles of use i haven't had a problem so at one time they must have been matching up.. and i do know alot about the wiring and how things work but i haven't dealt directly with this situation and i don't understand how they could all of a sudden be off. i didn't change gear ratios tires or anything else that would cause it that is why i didn't mention it and the questions intended direction was at the electrical aspect not the drivetrain. that is why i didn't understand why everyone was off on a tanget about the drivetrain. it has a madz28 tune as stated earlier that i got a month ago. everything worked wonderful. the other day my stepfather was driving the car and all of a sudden its not working right. so i swapped the vss out with another i had laying around with no change to the readings. so now i am stumped.
Speed is controlled by the PCM because when I swapped from M6 to the 700r4, I also used the 4l60e reluctor and sensor and could not get mine to read correctly until I had the PCM changed from 16 ppm to 40 ppm (something I could not do with LT1 Edit). Don't ask me any more questions cuz that's all I know, lol.
Originally Posted by joshh123
the speedo is controlled by the computer. so i don't see how the controlling unit could be off and what it is sending a signal to could be right? everything was working fine for the last few hundred miles of use i haven't had a problem so at one time they must have been matching up.. and i do know alot about the wiring and how things work but i haven't dealt directly with this situation and i don't understand how they could all of a sudden be off. i didn't change gear ratios tires or anything else that would cause it that is why i didn't mention it and the questions intended direction was at the electrical aspect not the drivetrain. that is why i didn't understand why everyone was off on a tanget about the drivetrain. it has a madz28 tune as stated earlier that i got a month ago. everything worked wonderful. the other day my stepfather was driving the car and all of a sudden its not working right. so i swapped the vss out with another i had laying around with no change to the readings. so now i am stumped.
again.. it was already tuned and working properly for some time.. now with nothing done to the car since i got it tuned now the reading is off in the computer and the speedo is correct...
anoyne else have a idea of what could casue it.. talked to ion aka madz28 and he said that it couldn't be a tune issue, that it was my scan tool? which i don't agree with, but i am still not able to drive my car..
