AdsoYo

First of all, on highway drives when I'm taking it easy and doing the speed limit I've always gotten between 22 and 24 mpg. On this trip I drove 287 miles from Redmond, OR to Redding, CA and used 10.3 gallons of gas. I had the cruise set to 60 through Oregon and about 68-69 in California. I had to pass a handful of semi's in 4th or 5th and dropped into 5th for a minute or two going up a hill. The only thing I can think of that was different during this trip than any other was that the kid who filled my tank in Oregon didn't put the gas cap on all the way. He had it on crooked and probably only caught one of the threads.

The lbl and rbl on the scanmaster read 116 and 114 the few times I checked and it was in cel 6. EGR was stuck closed, ccp was at 100.

From Redding to Camarillo which is about 560 miles I got 25 mpg which is still higher than usual, but not my glorious 29. That's with the gas cap on tight. How the heck did I get 29 mpg so I can do it again!?

sbs

Downhill.

Injuneer

Not unusual to see that kind of mileage under long-range "cruise" conditions, at least not from my experience.

3DFORMULA

x2..

johnny3986

x3... but I got 32 mpg coming home from NC after my mining internship

26 on one tank and 28 on the other after looking at my log while going out there. I was cruising in 6th for most of it doing like 80ish using cruise control.

93FIRETURD

Your computer also has a function that after about 3 minutes of sustained constant speed it leans the engine out more to use less fuel. It completley ignores o2 sensor readings and merely drops the amount of time your injectors are open.

WS6T3RROR

say whaaaaaat? lt1's are not equipped with lean cruise mode.

MadMike 97 Z28

ya im sorry but that makes no sense. i think someone was messing with you when they told you that. if it ignores o2 sensors then it has no way of knowing the A/F ratio. but if it did what you say (magically) it would seriously compramise the durability of the engine lean A/F = HOT

WS6T3RROR

Leaning the engine out at cruise airflow levels is no problem. Althought at some point mileage will fall off due to irregular combustion if you get it too lean.

JakeRobb

Proof?

WS6T3RROR

Jakerobb, I can videotape my dual wideband oscilating down the highway with the cruise on for as long as you want, you buy the gas . With the stock switchpoints it goes between 14.4 or 14.6 to 15.2 pretty reliably on both banks. I can also provide a mountain of datalogs where o2ms only changes with airflow.

6SpdLT1Z

I've got 29mpg in my SS before, 6 speeds get excellent highway fuel economy.

WS6T3RROR

As for the original post in this topic, the less time you spend accelerating and sitting idle and aslo at cold start the more your mileage is going to improve. You were also going at a pretty slow relative speed, above that fuel economy is going to fall off rather quickly. Cold starts and short trips play hell on mileage. Cold engine oil, coolant etc take a ton of energy to bring up to temp, where do you imagine that energy comes from? Thermal efficiency is related to temperature differentials and a cold engine is not nearly as good at rejecting heat from combustion as a hot one.

You probably also spent a great deal of time at the same airflow level rpm and vacuum and the computer had an absolute ton of time to converge on the propper fuel trims for that load point. Traveling from a high elevation to a low one will also alter results.

I have also taken notice that some gas station pumps tend to really aerate the fuel a great deal more than others and it will trip the auto shut off on the pumps much to soon. There is a shell station here that I can get another gallon and a half in my tank before it kicks off the first time. If I fill up at the station near my house after that and measure it by the first shut off it looks like my mileage is super good until i wait 30 seconds and finish filling the tank. If you try to run more in at the shell station though you're going to have to was gas off the quarter.

Critter

I've gotten as good as 38 on the highway, but i was in my wife's civic. That 6th gear is deep man. As long as your car is kept up on tune ups and you stay out of the gas you can do that consistently.

Not Dave

Way old thread!

In 2015 I did the long haul for the Hot Rod Power Tour. After just over 3,000 miles round trip my stock Z28 averaged 27 MPG for the entire trip. 30.4 after 115 miles was the best it's ever done (same trip, was in Illinois). Always run premium. Yeah, after 18 years it was still stock, that's the main reason I bought it.

I've read through many forums that these cars get the best mileage around 70-75 MPH.

I don't remember when I changed spark plugs, think it was after that trip. The old plugs were OLD, I don't think the #8 plug had ever been changed. I also don't believe the OptiSpark has been touched (cap and rotor changed). I bought the car in late 2014 and broke my leg 2 months after getting it. A new fuel filter is what it had before the trip with 17 inch SS wheels and 275 wide tires all around. AC didn't work so didn't run it.

For everyday driving it averages about 21 MPG and on the highway gets roughly 25-28 depending on several variables. Once got 17, once got 18 so normally 19 or better. Almost 13,000 miles in about 3 years so don't drive it a lot.

I've used Fuelly.com from day one to track mileage.