Transmission Overdrive

[The Gat]

I have an automatic transmission. I live at 2,050' elevation and I drive daily to 5200', the problem comes at 3800' elevation. The RPM's remain at 2,800 doing 80mph on cruise control, even up the steep sunset hill. The RPMs remain the same until I reach 3800'. I have noticed this everyday that it is at the same spot, the transmission downshifts and the motor is now turning at 3,150 RPM and remains until I go back south down the mountains.

Edit: Figured I should add this. At 3,800' when the transmission and rpms change, it is on flat ground. No incline or decline.

Does anyone know what can change this?
I have a stock 1994 4.0 OHV, automatic, with 235/75R15 tires.

Any help would be appreciated.

-Gat

 

[snoman6115]

prooly jsut atmospheric pressure or the thinner air

 

[alaskan155]

you loose power at the higher altitude, thus your engine is working harder thus you press the go petal more thus it need to kick down a gear


i drive between average between 5000-6000 ft(sometime 7 or 8 been to 14k twice) in elevation, compared to when i go to oklahoma where the elevation is lower and everything feels different(i mean it feels like my engine gains 20 to 40hp when i go to Oklahoma)

so it normal, just give it less gas and it shouldnt kick down

 

[The Gat]

Ok thanks! My dad said for me to take off my gascap again and try it because someone broke my locking one a while back. With it off, it increased fuel mileage and now I find that it also increases power! Gascap off and a clean airfilter, cruising 83mph just perfect. One problem though, it sounds like a can of rocks is rattling on my floor boards when I'm pressing the gas, does anyone know what would cause this? I know Rangers shouldn't be 55+. Ha ha.

I do not advise others to do it. Gascaps are there for a reason.

 

[Yellowsplash]

That sound would be predetonation...not a good thing.

...and your gas cap has nothing to do with power or fuel milage.

 

[The Gat]

That sound would be predetonation...not a good thing.

...and your gas cap has nothing to do with power or fuel milage.

I looked at a few postings on this "predetonation" or "pinging" and most responses were to burn a higher octane. The few last tanks have been 91 octane and this has cut out the noise. The truck and engine is now running quietly.

As for my gas cap, what I say is true. I burn 3/4 tank a day so I have plenty of proof in my log. I log miles for taxes. I run a tank with, then a tank without, and every tank without the gas cap, the mpg is on average- 19.57. With the gas cap, an average of 17.28. Also, the transmission will downshift on the incline of sunset hill when the gas cap is on, every time. It has never downshifted with the gas cap off. I am very anal about my truck because I do not trust automatic transmissions. To back it up, the electrical components on my fathers 2006 F-150 just failed this morning with 170,000ish miles. Sorry to be abrupt but I drive solo and it is a 1.5hour drive... Plenty of time to discredit my transmission and watch the tachometer.