I'm now scared to death of the 4so tranny in the 2004 RT 190P.

[booster]

Originally Posted by pasusan

Can anyone tell me if tow/haul mode would help? I thought I read somewhere that if you put it in tow/haul then the converter locks up which would help with the overheating problem.

???

I am pretty sure I posted the shiftpoint and lockup tables for tow/haul mode in the Chevies back in the programming thread.


For the most part the tow/haul mode raised the shift point speeds and actually delayed the lockup also, so would in some conditions probably make the overheating worse.


It appears the heat was not a consideration in the programming, just available power to move the van faster or to accelerate better when towing of fully loaded. When the converter is locked you lose the torque multiplication factor of the converter and rpm drops so the engine makes less hp and that is a double hit to available power to the wheels.


The six speed transmissions are able to lock up more of the time as they have more gears available to keep the rpm up at various speeds for the power to still make the van move well with a locked converter. Those vans also have more powerful variable valve timing engine that gets most of the gains at higher rpm, so well suited to go with the 6 speed.


In reprogramming the lockup on our 4 speed I missed the guess on how slow a speed it could go in second gear up a steep mountain, winding, road. When I slowed for curves during the climb, it did not unlock and wouldn't pull at the lower speed and we pretty much had to slow down more to get it to downshift or unlock. It took some experimenting to find the right balance of power available vs climbing speed to get it right.

[pasusan]

Originally Posted by booster

I am pretty sure I posted the shiftpoint and lockup tables for tow/haul mode in the Chevies back in the programming thread.


For the most part the tow/haul mode raised the shift point speeds and actually delayed the lockup also, so would in some conditions probably make the overheating worse.


It appears the heat was not a consideration in the programming, just available power to move the van faster or to accelerate better when towing of fully loaded. When the converter is locked you lose the torque multiplication factor of the converter and rpm drops so the engine makes less hp and that is a double hit to available power to the wheels.


The six speed transmissions are able to lock up more of the time as they have more gears available to keep the rpm up at various speeds for the power to still make the van move well with a locked converter. Those vans also have more powerful variable valve timing engine that gets most of the gains at higher rpm, so well suited to go with the 6 speed.


In reprogramming the lockup on our 4 speed I missed the guess on how slow a speed it could go in second gear up a steep mountain, winding, road. When I slowed for curves during the climb, it did not unlock and wouldn't pull at the lower speed and we pretty much had to slow down more to get it to downshift or unlock. It took some experimenting to find the right balance of power available vs climbing speed to get it right.

Thanks for that Booster - I'm going to print off your explanation of what gears to use for the hubby. We only overheated once - going up to Spruce Knob in WV.

[booster]

Originally Posted by pasusan

Thanks for that Booster - I'm going to print off your explanation of what gears to use for the hubby. We only overheated once - going up to Spruce Knob in WV.

Here are the shift points and torque converter lock/unlock points for the tow haul mode. Table if shift point up and down vs throttle position and mph. 255 means that point if not used. Note you have to be going at least 60mph and at 88%l or more full throttle to lock up in second gear. Almost no mountain climbs that need second gear to go up them will allow you to go that fast. Normal mode is 50mph I think, and that is also not at all common.


The table shows it as "performance" mode, but that is tow/haul in trucks.