Ok my truck (99 F-250 5.4 auto) sat for 3 weeks while i was on vacation, and i came home to a dead battery, which was no biggie, but then when i went driving around and got above 40 mph the tranny slipped out of gear. the only way to get it back into gear was slow down below 40. i immidiately checked the fluid and it is GOOD. so i drove it around some more and it continues to do this...i realized that when it slips out if i put the gear shifter into 2 it will engage in second gear and drive fine, and then i can shift it up and it usually holds fine for a while after that.
before i left i had absolutely no problems with the tranny. no shifting problems or anything. i change the fluid every 6 months and drop the pan to change the filter every year no matter what the mileage (it usually isn't more than 15K) and i am at that time of year to change the filter, but it has only been 10K miles so i seriously doubt that could have anything to do with it.
in town it has also been skipping second gear when i take off and shifting into 4th gear at about 25...totally weird.
any help would be greatly appreciated...also it does have a superchips power programmer and i set the shift settings to be more firm, don't know if this would have anything to do with it though. like i said, before it sat it had not a single problem.
thanks

 

Hmm, that is a bit strange.

Possibly, when your truck lost the battery, it cleared the computer. Usually when the computer is cleared, you start it up and let the truck run for 10 minutes or so to set it's initial setting. then drive it around abit to let it "learn" your driving style. Maybe this is what happened. You might have to disconnect the battery for a few minutes to make sure any bad settings you might now have are cleared.

Alternatively, a sitting truck makes a nice comfy home for little beasts. Check the wiring and vacuum hoses for evidence of mice etc. Sometimes they will chew up you wiring and hoses and make weird stuff happen.

You might also check the shift linkages and cabling to the tranny to make sure the linakes are not rusted up and the cabling not chewed up or corroded.

Any codes or does the overdrive light flash?

Good Luck,

Jim Henderson

 

Is the OD light blinking?

 

im sorry i completely forgot to mention the o/d light is not blinking. i noticed something else as i was driving it some more. it started to feel like it was slipping out of gear again at slower speeds (25 or so) and instead of letting of like i had been doing i hit the gas just to see what it would do, and when i did that revved up and caught first gear...but it was like it downshifted not slipped, because everytime after that if it felt like slippage i would hit the gas and it would drive in first gear, and then shift shortly after...totally weird. everything looks good under the truck, linkage, wiring etc.
i am going to disconnect the battery again and the start it and let it idle for about 10 minutes then drive it again.
updates to come.

 

Does the speedo act up when it does this?

 

no, speedo is fine the entire time

 

This sounds like it needs to be monitored by a scanner that has data stream capabilities, This transmission is electronically controlled and it will do as it is told by the computer.

We need to determine if it is a control problem or a trans problem.

 

UPDATE: out of nowhere, the trans started running perfect again... I guess the computer just had to relearn how to shift, i just think it is kind of weird because i have had it sitting for 3 months with the battery disconnected and it didn't have a single problem.
but, after driving for three days with it shifting at odd times (downshifting into first at 35 and into overdrive at 25) all is well now.

 

I had a similar problem, only slipped when making right turns. The wire harness was between the body and frame and was pinching when it leaned.
pulled it out cleaned it up and rewrapped the harness.it was fine.

 

The real question is....Why did your battery go dead in the first place? I regularly let my SD sit for a couple weeks at a time and it always fired up.

Maybe something in your ECU is going out and draining the battery and hindering the shifting all the same.

 

You know, I found the tranny wiring harness pinched the same way when I was under my '01 a few months after I bought it - glad I found it.

 

you know what i was thinking the same thing, about why the battery went dead in the first place, i know i have a drain somewhere, you might be onto something with the ecm draining it. its a brand new battery and shouldn't have drained.