in and out of overdrive

[joeyd50]

Hi guys, this is my first post,I hope you can help me. I have a 1994 Nissan pick up 4X4, 3.0 motor. My truck keeps going in and out of overdrive, I could have the cruse set on 65 and everything is find the trucks in overdrive about 2500 RPM then I`ll start to go down a little hill and the truck will downshift and jump up to about 3700 RPM, then once it starts to accelerate it goes back in overdrive and 2500 RPM again, till I start to go down hill then she`ll downshift again. It`s not just at 65 MPH but anytime I`m in overdrive it will go in and out. Any ideas whats wrong with my truck?
Thanks
Joe

[joeyd50]

Come on guys, somebody, anybody, HELP!!!!!. Does anybody know how to adjust the TPS????
Thanks
Joe

[kave in]

hmmmm... maybe its not even jumping in n out of overdrive but just changing gears, just like you said... that happened to me when i was driving a 95 altima sometimes id even be at high rpm for 2 secs then low for 2 secs the high n repeat the cycle. so heres my theory... cruise control is supposed to keep the car going at a set speed. when a vehicle is going uphill at a high gear it will lose momentum n slow down slow enough that the high gear will no long be able to keep it going at the set pace so it downshifts to speed up and reach the speed. when that speed is set it will shift to a higher gear then lose momentum n repeat the cycle.

you can even try this with cruise control and overdrive off. drive on a freeway that has a flat surface then suddenly goes uphill. approach the hill at a steady pace (lets say 65), n make sure the rpm remains the same. as you go up the hill, rpm n speed will drop (below 65) so youre gonna have to push the pedal harder down. but itll be harder to accelerate going up hill so youll push the pedal harder n the car will shift to a lower gear which means higher rpm.

[dcobb]

It's under warranty right, so call the dealer and talk to the service guys if you think something is wrong. Use that warranty you paid for... The cruse control intelligence is designed to maintain a certain speed and on flat level streets will make subtle corrections to do this and will seldom require a shift (unless you are towing something or have a lot of weight in the truck in which case you should always disable overdrive). However since it can't anticipate slope changes, it will react to the change and overcompensate a bit until it reaches the target speed again. So yea, if you are doing fine on level ground then start going down hill to the point where you slowly start speeding up, the up shift is intentional because it's the only way for cruse to slow the truck back down to the target speed. On the flip side, if you are going up a steady hill it will downshift to get to get up to the target speed then ease off the gas possibly causing a shift into overdrive and do this repeatedly. This continuous shifting effect is also subjective to the set speed of your cruse as well. Meaning at certain speed ranges you will naturally be in between gears. Another example is if you are going around 35-40, the truck would naturally want to be in Overdrive if on level ground, 3rd if it’s a slight grade, and even 2nd if it’s very steep. So think what would happen if you tried to apply cruse control in that condition, what a mess if you're in D

If you love cruse control that much, set the cruse at a speed and be smart about it and do the shifting manually. If you are on the freeway with a lot of minor ups and downs, switch off overdrive. If you are going up a steady grade at around 35, shift into 2nd and set the cruse. In other words recognize the limitations of the cruse control and remember it's dumb and only cares about the target speed as it doesn't anticipate or even understand hills and cares not about excessive shifting. If you are experiencing excessive shifting on steady level ground, then there’s something wrong and you should take it in.