why,why,why,why,why?
08-16-2005, 11:35 PM
#15
5th Gear Member
Join Date: Jul 2004
Location: Westminster, MD
Posts: 4,343
RE: why,why,why,why,why?
O/D is just forth gear. It doesn't have anything to do with taking off or added performance. Turning it off just doesn't allow the car to go into 4th gear. With my v6 if I stomp it off the line I can spin until it hits about 3k rpm then it hooks up. I don't hold the brake or anything. With the factory goodyear tires I could spin even more.
ends up looking like this
08-18-2005, 11:59 AM
#20
Join Date: Aug 2005
Posts: 6
The long answer
The overdrive Button does more than it uses to do. Used to (Pre 90s) the O/D switch only controlled the transmission and just locked/unlocked the torque converter to give you an overdrive.
Now days when you push the O/D button the EMC (Engine Control Module) or EMC (Engine Management Computer) selects the O/D limits. When this takes place the ECM retards the timing the fuel mapping and changes the shift points in the Transmission. Even if you manual down shift the transmission or floor the gas the ECM is still looking at the O/D limits and will limit the timing, fuel mapping and the transmission shift points. You will take off but you will still be leaving some performance behind. For instance In O/D the red line might be 7500rpm and with O/D off the rpm limit might be 8200rpm. Same thing with the rest of the limits.
When you turn the O/D off (at a standing stop) you increase limits that the ECM will allow(sort of like a performance chip).
Think of it as two different modes. O/D off will allow more performance from the engine, O/D on limits the engine performance. Just like having two different control systems on the same car and switching from one to the other.
Hope this helps.
Don
Now days when you push the O/D button the EMC (Engine Control Module) or EMC (Engine Management Computer) selects the O/D limits. When this takes place the ECM retards the timing the fuel mapping and changes the shift points in the Transmission. Even if you manual down shift the transmission or floor the gas the ECM is still looking at the O/D limits and will limit the timing, fuel mapping and the transmission shift points. You will take off but you will still be leaving some performance behind. For instance In O/D the red line might be 7500rpm and with O/D off the rpm limit might be 8200rpm. Same thing with the rest of the limits.
When you turn the O/D off (at a standing stop) you increase limits that the ECM will allow(sort of like a performance chip).
Think of it as two different modes. O/D off will allow more performance from the engine, O/D on limits the engine performance. Just like having two different control systems on the same car and switching from one to the other.
Hope this helps.
Don