Strange Overdrive Action
 

When I turn off my overdrive and get on the gas and then go to put over drive back on again...the RPMs seem to jump anywhere from 500-1000 higher than what they were before I hit the button, the car then shifts...sometimes roughly. I found this odd, because it had never done it before...normally I would put OD on and the car would shift immediatly. What could be causing this?

In 3rd gear, when O/D is off, the torque converter is locked. In 3rd gear, when O/D is on, the torque converter is unlocked. I believe what you are experiencing is the torque converter unlocking, thus higher RPMs. A 500rpm increase seems about right, but I don't think a 1000rpm is normal...

Re: the rough shift - perhaps associated with the amount of throttle you're giving it?

Well I have also noticed that when accelrating at a slow speed, as well as fast...the RPM gauge seems to resemble a second hand on a clock. What I mean is that the needle tends to tick instead of slowly and steadily moving. You can also hear in the engine that it is lagging.

Also I noticed that if you do decide to get on the gas, regardless of OD being on of off...the engine lags and then the RPMs jump to about 6k and after a while it drops the gear and takes off...but its really rough. I realize when stepping on the gas like that, that the RPMs should jump..but I have never seen a car do it like this. Something is slightly off.

The torque converter does not lock up in 3rd gear, ever.
It only locks up in 4th gear, overdrive on.

Sounds like the gearbox is slipping to 6k rpm and then catching and coming down again.... :easter:

could this have anything to do with the knock sensor...it has been throwing the code.

Nah my Knock Sensor is throwing the code too and I don't get that O/D behaviour

ARE YOU SURE ABOUT THIS?

When I still had my auto tranny, if you go WOT with O/D off around 80mph (3rd gear) and then turn O/D on while still WOT, the RPMs will quickly jump a few hundred RPMs and then continue rising.

Likewise, if you go WOT with O/D on around 80mph (3rd gear) and then turn O/D off while still WOT, the RPMs will quickly fall a few hundred RPMs and then continue rising.

THIS IS THE SAME FOR EVERY AUTO MAX I'VE DRIVEN (3rd, 4th, & 5th gen). I doubt it is air/fuel/ignition map related. I believe the TC locks up in the highest gear possible (3rd when O/D off; 4th when O/D on) for the sake of fuel economy.

I was schooled on this same topic way back in 2001. :)
http://forums.maxima.org/showthread.php?t=59471

Yes I'm sure. Our cars have a 4 speed automatic with a locking T.C. The lock up will happen in 4th gear, tranny up to operating temp, speeds over 31MPH crusing with little to no load on the engine. It will never lock up in 3rd gear, the logic doesn't allow it to. With O/D off, your driving a basic 3 speed automatic.

At WOT, no matter what gear your tranny is in, the TC wouldn't be locked. It only locks up when your crusing, 4th gear with little to no load. As soon as you step on the gas harder to accellerate, the TC unlocks.

Then how would you explain the 3rd gear phenomenon that I described above? Try it and see for yourself.

Also, I pulled up these relevant threads for everyone to read -
http://forums.maxima.org/showthread.php?t=279710
http://forums.maxima.org/showthread.php?t=32430

ladies and gentelmen.... our cars are 4 speed automatic... meaning that 4th gear is the overdrive... which the torque converter locks in... if u turn off the over drive then u have only 3 gears to go with... when the overdrive is turned off the car will experience higher revolutions in all the other gears...

ladies and gentlemen.... True, we do have a 4 gear tranny, BUT, we also have a "quasi" 5th gear which is the TC locking in 4th. I'm sure you've all experienced this while cruising on the freeway - you give the right amount of throttle so that the RPMs will initially jump a few hundred RPMs and then accelerate, but not downshift to 3rd. Since the tranny did not shift to 3rd, but the RPMs did jump, were you initially in 5th gear and are now in 4th? Do we have 5 gears? No. What you just experienced is a locked TC unlocking itself in 4th gear.

As for the 3rd gear phenomenon that is described above (as well as in the other threads that I listed), the TC certainly can certainly lock & unlock in 3rd. See for yourself! DON'T KNOCK IT BEFORE YOU TRY IT! :) Try it and if it doesn't work for you (it's worked for everyone else who has tried it), then reply.

Again, turn O/D off, floor it when you're at about 80mph, turn O/D on while still WOT. You WILL notice the RPMs jump ~500 rpm, but not shift to 4th. This IS your TC unlocking in 3rd.

Calsonic is right.

You are accomplishing nothing by turning OD off before stepping on the gas. Any time you ask the car for much more than steady speed it will unlock the torque converter on its own....give it more gas and it will grab a gear....to the floor it might go two gears.

That button is design for one scenerio.....stop and go driving at speeds were you would get into overdrive just before you step on the brake...(over 40mph?). Staying out of OD then saves some wear and tear on your converter. Unless you fit that scenerio, or are looking to top out your Max on a suitable road, just leave it in OD.

Well all this is good to know...but it still doesnt explain the behavior that im experiancing.