Speedo Calibration Computer Function
Thread Starter
|
Senior User
Joined: Feb 2000
Posts: 175
Likes: 0
Speedo Calibration Computer Function
Can anyone definitively answer the question of whether or not the computer(driveability) of a 93 F150 4.9l would be adversely affected by an incorrectly calibrated speedo which is the result of a tire size change? The change was from stock 235's to 33x10.5BFG's.
I asked a Ford Dealer Parts Deskperson once and he said no but I would like to know for sure.
Thanks,
WHaynes
-93 F150-
I asked a Ford Dealer Parts Deskperson once and he said no but I would like to know for sure.
Thanks,
WHaynes
-93 F150-
Thread Starter
|
Senior User
Joined: Feb 2000
Posts: 175
Likes: 0
Speedo Calibration Computer Function
I do have a manual tranny so, shift points aside, does the computer on a 93 need the "true" speed to set up parameters for the EFI.
Thanks for your reply
WHaynes
-93 F150-
Thanks for your reply
WHaynes
-93 F150-
Elder User
Joined: Jan 2003
Posts: 539
Likes: 0
Speedo Calibration Computer Function
No, It will not affect the computer. The computer measures only parameters from the engine sensors. Another way of looking at this is: you may run 3K rpm in any gear at different speeds. The computer does not have seperate fuel/spark maps for each gear, it only has one and it is variable to load measured by vacuum (e.g. the MAP sensor).
Fleet Mechanic
Joined: Aug 2001
Posts: 1,526
Likes: 0
From: Round Rock, TX
Speedo Calibration Computer Function
Except for all those other pesky computer-controlled things, like ABS, cruise control, etc., which WILL be affected by not changing the conversion constant.
It takes about 3 minutes to change the constant; I'd recommend doing it.
It takes about 3 minutes to change the constant; I'd recommend doing it.
Elder User
Joined: Aug 2001
Posts: 508
Likes: 0
Speedo Calibration Computer Function
If you didn't change the speedo gear, then the computer likely wants the "false" speed. On GM's it is common for the computer to use the ratio between MPH and RPM to determine what gear a manual transmission is in (or if it is out of gear). It uses this info make some minor adjustments. I don't know if Ford does the same thing.
