grinder11

Wife and I made it to Florida without issues, except 1 puzzling, but positive change; as I got into the lower elevations, like 100-150ft above sea level, my fuel mileage increased a noticeable amount. I NEVER get mileage like this at home, where my altitude is approx 750-1,000ft above sea level. With the cruise set@75mph, the readout was consistently 27-28mpg. I've owned the car a long time, so I know it pretty well. At home, it seldom gets above 24mpg on the readout. I know from experience the readout is about 3mpg on the optimistic side, and that 24mpg would actually be about 21mpg. So, all of a sudden, I went from 21mpg, to about 24-25mpg. Anyone care to wager why this substantial increase happened? There was no wind change, in velocity or direction. I'm thinking my tune is a bit rich@750-1,000ft. altitude, and the richer oxygen level of the 150ft altitude leaned the air/fuel ratio to a more efficient ratio. But then again, I thought that the pcm and sensors would automatically mix the air/fuel ratio for optimum whether at 100ft, or 1,000ft? Thoughts???

CrystalRedZ07

Lots of variables to take into account based on just one trip - repetitive trips under the same conditions would be more conclusive. When I get variations, I also have to pay attention to how much fuel I added after the fuel nozzle shuts off, which can affect results.

grinder11

I hear you on that, but my readout changed to a level it normally never sees.....

ClothSeats

The reason may be because your long term fuel trims need time to adjust, so even though the MAP sensor and PCM were aware of the higher air density, it takes time for the fuel trims to become convinced.

scary10

the DA without a doubt affected it. I've gotten 37mpg cruising on the highway at 75mph

grinder11

Not a tune guy, but if LTFTs take a bit longer to calibrate correctly, that sounds logical to me. I wonder what kind of power increase I'd see running at a strip@100ft above sea level vs a strip@1,000ft above sea level? I'm thinking I'd pick up 10-15hp. But-DA here in Florida would probably be more important, considering the high humidity here vs home. Thanks to all who gave their opinions. Exactly what I was looking for.........

AzDave47

Power decreases about 3% per 1000 ft. gain in elevation for NA engines. I run events at 7000 ft DA and lose about 24% of my sea level power.

When I brought my C6Z across the country from NH to AZ I started getting better fuel mileage as I got into the 4000+ elevations in NM and AZ.

rockinSeat

Umm tire pressure? Did you inflate? If you go to lower altitude, tire pressure will decrease, so I'd have thought you'd get lower mileage.

grinder11

No inflation by me, but mild inflation by temp. I picked up 2-3lbs due to proper inflation in 55° temps at home, to 85-90° in Florida.....

KB9GKC

Hello Grinder11,

The most reasonable and usual explanation is a tail wind.

I've been watching gas mileage closely for many years, it's an excellent way to examine a vehicles overall condition.

Be Well,

Douglas

grinder11

Thought I'd update this thread. So, wife and I went to Mt Dora and back today for their big arts and crafts show. Approx 180 mile round trip. Filled before I left. A lot of stop and go in Mt Dora, looking for parking. Plus many 2-3 minute red lights. Anyway, readout still up, and I'm 1 mark over half full in 180 miles all around driving. Gauge is usually at 1/2 tank, or a bit under, when driving like this. Readout still showing 2-3 MPG higher than usual at 70mph. It read the same, going N., then E., and coming back, S., and W. Not complaining!!! Hope it continues, and car ran great. Guess car likes Florida......

phils C5 vette

Cooler weather also helps.

grinder11

I'm not following you here. I left Michigan with temps in the low 40s, and it just got warmer the farther South I went, culminating in the mid 80s when I got to Florida.......