Hey guys, we are up in the mountains and noticed a loss of power. About 50 mph the truck just didn't seem to have the kick it should and felt very sluggish. Haven't been up in high altitudes, could the high altitude Jack that much if at all? Could my Evo have anything to do with this?

 

You'll lose about 10-12% HP per 1000' of elevation. My Bronco at 11,000' won't hardly pull itself. At 14,000', it's low range only and unless you like walking, you'd better not turn it off. It will not start at 14,000'- not near enough air for it.

 

10-12% per 1000 is a bit high I'd think. Maybe more like 4-5%.
I live in Salt Lake and we are at 4,500 feet more or less and there is no way my truck gains 50% more power when I go to sea level MAYBE 20% I agree high altitude can affect power output but with fuel injected computer controled engine the affect is much less. Carbureted engines are affected more because its impossible to adjust the engine for a short trip up (or down) But even those if adjusted for the altitude wont loose that much power. I live in the mountains and travel frequently to as high as 11,000 feet. Yes they turn into dogs that high. The hills kill them to.

 

5% per 1000 is what I remember. There is less oxygen per volume of air, so your PCM matches that with less gas. It's just the opposite of what a super charger does.
The last car I had in the mountains started with 64 hp (1.7L) at sea level.

 

My wife and I went to Breckenridge Colorado on our honeymoon. My truck wasn't the only thing that lost power at 9,000+ feet. I was out of breath just sitting on the couch, and my head hurt for days! The first day we arrived, I decided to walk about 1/2 mile up a fairly steep hill. I didn't think I would make it!!

My house is at 352 ft elevation.

 

could the truck be in need of a tune up???

 

Ok we made it back from the mountains - Breckenridge, CO. So as I mentioned, the truck ran strong for about 500 miles to Denver, then we hit altitude and the power was left in Denver. Low end was fine but high end was not there, which was fine I guess because all I needed was low end to climb all the other snow covered stuff for three days. I really didnt think that the altitude would dampen the power that much, but when we came back down to Denver, the power rejoined us. I was more curious about if I could have changed the settings on the Evo to correct for the air/gas mixture in high altitudes and since I will be traveling that way again soon, I should probably post in the programmer section as well. Great trip overall, I suggest everyone take a trip to the mountains!

 

Yep, about 5% for every 1000 ft. I recently moved from San Francisco Bay Area (approx 300 ft elevation) to New Mexico and live at 7200 ft. All of my vehicles are way down on power. Hills that the 97 Expedition used to pull in OD with converter locked up in CA are now downshift to 3rd and unlocked converter to maintain speed in NM. More revs don't hurt the engine as long as they are not excessive. Just noisier and lower mileage.

As a side note, I also noticed my air compressor takes longer to fill - same thing, less pressure on the air intake. So it takes longer to fill the compressor. My rough calculation indicated I lost 27% of atmospheric pressire from 300 to 7200 ft.

High altitude is one area where a larger engine is definitely beneficial. Artificial air supercharger or turbo is even better! But my Expedition 4.6 is just stock and sufficient for normal driving and light utility trailer towing. I have a big 1-ton dually for serious towing.