bad gas mileage when traveling to lower altitudes

My truck an I live @ 8300ft in the rockies, bought it new in 2000, has 131k miles, 3" lift, 16"tires, I get about 18-20 mpg, however, when traveling down to lower altitudes, the gas mileage drops sometimes down to 14mpg. A friend says I should disconnect the EFI fuse for a few minutes, then plug in, to see if it will recalibrate. anybody else had this problem? thanks in advance B

 

Nope. I drove 950 miles, from 4800ft, to 5 feet, and back. Over a week ago

It took a several tanks of gas , but once I got there, I got better fuel economy.

Probably due to the fact fuel grades are 89,91,93 around seattle
Instead of 85,87,91 where I'm at.

But if it's a simple day trip, don't expect instant results.

 

It's not the octane, it's the mixture.

Lower elevations, the air is more dense, so the ECU injects more fuel.
You're making more power, but burning more fuel to do it.

I've had several vehicles that normally get 16-18 give me 22 in Utah.

 

this could be complete BS but my mech friend told me to open up the throttle, ie floor it all the way when i get to the valley because we live in the mountains.

he says it opens a vacuum or something or air mixture ... i've been drinking sorry

 

It's BS

 

Well it was for my old 1st Gen, but ya I agree BS.

He says it has to do with oxygen levels in the air and by opening the throttle fully you release or create a vacuum or something ... Mmm beer

 

what the hell, I'll try your advice BS, what have I got to lose except for a little more gas consumption, I will drop back in in a few days after the trip to south Texas, give an update, thanks B

 

At lower altitudes you should get better mileage. And increased horsepower. More oxygen gives better combustion, more efficient combustion. The fuel/air mix is higher, but as it burns better you actually use less.

I live at altitude too, not as high as you. I average 18-20 mpg locally.
I drive to Kalifornia every couple years and average 20-22 mpg on the freeway. Best ever was just over 23 mpg. Happened one time only.
But around town at lower alt. I get way less.

Only reason I can think of is that I'm enjoying that extra HP just a little too much, kind of fun to stomp on it and go. Almost like a little turbo. Aggressive driving habits take over. Not to mention it's Kalifornia and you have to be aggressive anyway...
The ECM will make any changes it needs to as you change altitude, no need to pull fuses or go WOT for some vacuum nonsense.
Try driving easy while in Texas and I'll bet you see an improvement.

 

IIRC I got substantially better fuel mileage when I drove through Colorado - but I had a turbocharged car, which doesn't really care so much about air density. It just squashes it into the engine anyway.

 

lol. Do any mountain driving? This can really screw with mileage.
Drive up and your mileage decreases, drive down and you get incredible results. Combined you get what looks like pretty decent mileage.

Years ago I had an old Scout 800 with a 266 V8, Holley 2bbl carb.
On a trip to Silverton CO to do some wheeling the thing ran like crap, gas mileage sucked, was literally pouring gas down the carb as I had the pedal to the floor to get it moving. There was a Napa in town and they just happened to have Holley jets. I took her down two sizes and problem solved, ran much better but not quite as good as on home turf. There simply isn't any oxygen at higher altitudes.

My current Scout is a TBI setup and I will never go back to a carb again.

Modern ECU's take care of this little problem, that's what the O2 sensor is for.

Arguments have been made about the ECU running leaner at high altitudes, therefore using less gas, vs running richer at low altitudes, using more fuel in the mixture. This is true technically... but it comes down to efficiency, engines run more efficient at lower altitudes, therefore they CAN get better economy. Driving styles vary, so will your mileage.

 

I went all the way across east to west - part of my 4,250mi drive cross/around the country two years ago.

 

His logic is based in fact, but rapidly opening your throttle won't change anything. The system is self-balancing, and pressure change is so slow that your system is always in balance.

30 years ago before MAP sensors and EFI? Ya... a carbureted engine properly jetted for sea level would be slobbering rich at 5,000ft, get horrible mileage, smoke, and suffer from a lack of power.
Rejetting would pit it back into balance until you returned to sea level.

Motorcycles... it's only been the last 10-12 years that EFI has taken over fuel control. My Vulcan 1600 gets 33mpg here in SoCal. It got 55mpg in the mountains of Utah from Escalante into Nephi.
Another guy with an older carb'd bike (same destination, different group from Seattle) barely made it over Beartooth on his 1500.

But even in those days, rapidly opening the throttle would not make a difference.