Two part question.

First, I seem to be gear hunting like crazy from 67-73 when going up hills. And I do mean hills, I am not traveling through mountainous areas. I am hoping to write this off as normal behavior and that turning the OD off will solve this. Is this normal, or do I need to start looking for problems? If there may be problems, any hints or suggestions? Im a college student (limited budget), and Ive worked on a lot of cars, but never a transmission.

Also, this is my first time owning anything with an auto trans. I have a 97 F150 4.6 4x4. My only experience with turning off overdrive was when I was a kid in my sisters car. I decided to push the button while she was cruising along and it scared the crap out of her and I caught hell for it. Needless to say, I aint done it since. Is there any harm in dropping out of OD at around 70mph?

Thanks

Adam

 

What do u mean by excessive? U talk about hills...thus...if you go up one it will downshift.....then when you go over...it willl upshift....and if the hills are close togther then yes...you will excessivly shift in and out of OD.

Now...if it shifts in and out of OD while going up the hill....then you got a problem.....and it must be looked at.

You only got a 4.6.....just take it out of OD and leave it out in hilly areas......

The best thing you can do...is not let it short shift....no in and out of od...thats why the button is their....turn it off...

 

Youre correct. It goes in and out of OD. It will start bucking. Is this unusual, or just something thats normal with the 4.6 and they gearing?

 

my 2002 does the exact same thing.. always has.. dealer couldn't find the problem.

 

It's "normal" in the sense that the trans is doing what it's programmed to do......

Do you have larger then stock tires with the stock gears?

Even with stock size tires and say the 3.55 gears, you might get this even on rolling type of hills....

What is happening when you are going up even a small hill is that the engine will start to 'bog' down due to the .70:1 gearing of the OD and the engine is just lopping along at say 1800 rpms... Well below it's peak torque rpm. As you slow down, you press the gas pedal harder, which triggers the TPS (Throttle Position Sensor). This tells the computer to downshift the trans into third. When that occurs, the engine is now in a better rpm range and you now pick up speed, so you let off some on the gas pedal. Since the computer does not know you are STILL climbing the hill, it goes ahead and shifts into OD, but then it starts to bog again.... Now the cylce is repeated.....

When you get the bucking part, you just happen to be at a spot in the program that wants to downshift AND upshift at the same time.... Basically, you are confusing the computer. At that point, is when you should manually turn of OD or give it some gas and let it settle (and then turn off OD) and let it stay in thrid until you are at the top of the hill. Then turn OD back on and continue on your way. On the next hill, what you should do is go as far as you can until it downshifts into third, At that time, turn OD off and climb the hill at whatever speed you want. When you get to the top, turn OD on again and wait for the next hill.

Even though it's an "automatic" and the trans is computer controlled, there are just some road conditions and driver ways that the computer just can't predict or adjust for...... That's why they have the ON/OFF button for OD.

Once you get used to the way your truck behaves on the hills, you will be able to know when you need to manually turn off OD and when you don't. Bascially, the best thing to do is if in doubt, turn it OFF.... That way you are not shifting in and out all the time and that's harder on the trans then just letting it rev at 2500 rpms for a short period of time....

Heck, when I tow my travel trailer, I usually just turn OD off from the start and it's in third for the entire trip.... Stay at 2500 rpms for hours..... Even when it will go into OD while towing, it's usually not long enough to make any difference in mpg anyway, so it's not big deal.... I get 10 mpg towing whether it's in OD or not.....

Good luck!

Mitch

 

Thanks Mitch. Ive been noticing the gear hunting has been getting worse. Same road, same conditions. I also noticed, while checking my vitals yesterday before a 4 hour trip, that my air filter is pretty well clogged up (being Easter I couldnt replace it right away). Would this limit my power enough to exaggerate the gear hunting?

Also, today when I firsted started my truck (it was in drive with my foot on the brake) there was a pulse every 10-15 seconds. It was enough that you could feel it as well as hear it. There was no change in RPMs. It went away as soon as I started driving. It may have something to do with my brakes, because I have noticed they grab A LOT more when I first start the truck up in the morning...then they get back to normal after even just a minute of driving.


Any thoughts?

 

Any to answer your question, everything is stock, including tires.

 

IMO, the dirty air filter would contribute to this..... The only reason I say that is I've noticed the same thing on my truck....

I've got a K&N, and when I've taken it out to clean, I put the stock paper one back in for a day or so (while the K&N dries and is re-oiled). I notice that my truck will down shift on the same hill that it normally does not downshift on. This is from third to second, as it's a steep hill in my neighborhood (35 mph speed limit)..... The stock filter is basically brand new too..... It does the same thing each time I use it.... Stock filter, downshifts up the hill. K&N, no downshifting....

Dunno.... That's just my observations on the air filter thing.... I do have larger then stock tires, but have the 5.4, which has a little more low end at lower rpms then the 4.6....

As far as the 'grabbing' goes, it could just be the TC since the fluid is cold and things have not had a chance to move yet....

Mitch

 

Thanks Mitch. Maybe if it stops raining Ill be able to get the new filter in. Im also going to change my trans fluid when I get home in a month. I dont know whether or not its been done before, but I would have to assume it has from the condition of the truck. 70k on it now, so I figure its halfway between 'first change' and 'dont change if its never been changed'.

 

Ok, I am running the 4.2 on flat to slight hill roads as well and have the same issue. I replaced the Digital Range Sensor after it coded the ECM, but experience the same issue. If I am running from 55 to 70 in OD and slighty ease in the gas as to gradually over take, it will try and downshift making that bucking or sensation the tranny took a crap on you. If I press harder into the throttle it will then force the downshift into a lower gear usually second, i think. It just never seems to find that medium and stay in 3rd. Just feels the tranny is slipping. I am running 4.2 on 3.55 with 1.6in over dia tires. Is there any ideas, and why doesn't it trigger the light? Thanks John.

 

I had same problem with tranny searching for a gear while in OD and slightly easing into pedel, it would jerk back and forth between gears until I pressed the pedal down farther. I had had a tranny oil change 20+ some thousand miles before, and I was also getting shudder. The tranny oil change I recieved before was a drain pan and change filter and refill. Not good since they didnt drain all fluid. So this time I ended up getting a complete tranny flush and filter change and all my problems went away. Make sure you use the Mercon V tranny fluid.

 

Hrmmm...I changed it the last time too which wasn't too long ago, I used the Merc 5 but just did the filter and drained the Torque Converter, but didn't blow the lines out this time. I guess I will wait and get it back to the US and get it done. I am leaving Germany with it in a couple of months. I am concerned there maybe some dirty contacts or something. This Tranny has never been overhauled or had any work, besides services.