2nd 'Map' In OEM ECU?

[richie9mt]

My '06 4.0 V6 w/auto trans seems 'peppier' with OD off compared to engaged. Is there a second 'map' for each mode???

I know there is a 'limp-home' mode, but this is definitely not it. The car just seems to accelerate more 'crisply' with OD off.

I've always thought that the OD Off switch just shut off shifting into 5th gear.

Anyone have similar impressions on the perceived difference in modes?

 

[Samos3]

Alot of OD equipped cars shift into OD early if the throttle is light. My 90 Safari van does it about 45mph.
So, yeah, with overdrive off, it should feel a little different.

 

[richie9mt]

Alot of OD equipped cars shift into OD early if the throttle is light. My 90 Safari van does it about 45mph.
So, yeah, with overdrive off, it should feel a little different.

Interesting. OD is active in all five gear ranges? Not just disconnecting fifth?

 

[Samos3]

No, I wouldn't say that. But my van, at light throttle, will upshift into OD as soon as it hits 42-45. If my foot is a little heavier, it may delay shifting in each gear a little longer. Sometimes it feels like it goes from second to OD or 3rd is just there for a really short time

For fuel economy, getting into overdrive as soon as the load and speed allow is a big thing. I think there are some automatics that will skip gears if they are not needed, like slow lazy acceleration.

Some of this also explains why at times it seems like it wants to bounce in and out of OD when on backrooms with gentle, short up and down hills at a fairly steady 45-ish. Like it's not flat enough to just stay in OD, but the short inclines tell it to downshift.

Also, I do believe that OD is not recommended for around town. Mainly highways and interstates with 50+ mph speeds.