NJD

I just bought a 2002 C5. I traded my 93 in for the 02. However, I notice I'm avg about 18 MPG on the highway. How, or what can I do to increase the avg highway MPG to what it should be(23-26 MPG).

Thanks

jkru617

Is the 02 stock?

NJD

.

I don't thing so, as far as I can see..

DEnglish29

My C5Z get 18-20 around town & 26-29 highway (not stock)
Never heard of anyone getting 18 highway driving

MY1STPEWTER

My h/c auto with 3:42's gets 27 or 28 hwy. Something doesn't sound
right.

GoldenFlame

A simple tune up can't hurt. (Plugs, Wires, Air filter, Fuel Filter)

I get around 21 combined going WOT very often, and about 26-28 HWY.

Evil-Twin

Because you are new to a C5, I cant assume anything..
If you haven't reset your DIC. you need to do that first to check highway driving. when you zero it out, it will vary greatly of a shor period of time.. the DIC is very sensitive to change. simple things like coasting can make a dramatic difference on average mpg. the more you drive the tighter the av mpg will get. in one day for example you can take an hours drive , set the av mpg to zero while doing 60 mph. after an hours of uninterrupted driving you should have an idea how good the car is at optimum highway driving speed with little variation in the speed.. but in the next hour you can dramatically change that number by changing speed or driving to an area with lots of up and down hills. the best av MPG can be achieve on a highway in a relative flat state like NJ. if you drive in combination of city and highway your mileage will drop. You have to fully understand the tool before you can accurately read the data. if you have a weekend filled with city driving in the computer then go out and drive on a highway for 20 minutes the city driving already embedded in the computer will effect the highway mpg. the longer the computer goes without a reset, the more accurate the overall mileage will be. if you have six months of city and highway driving embedded and then go out to check highway mileage you have to erase any previous mileage.
Bill aka ET
I have regularly posted 33 mpg driving to Atlantic City on the Atlantic City expressway where there are no hills. setting the cruise to 70 and letting it control the speed demand on the motor will yield the best mpg. Once over the bridge and into New jersey I reset the read out to zero. If I set reset from my house and then drive through the city to the bridge and then to Atlantic City and then into Atlantic City where there are lights on every corner and then back home, a totol of 145 miles I get 28 mpg.
Driving around town for a month with little or no highway and never seeing 5th or 6th gear, I average 12 to 14 mpg.

Bob Chapman

There's a problem. My 02 C5 six speed gives me 31-32 mpg at 64 mph and 27-28 mpg at 80 mph on the highway. I get around 20 mpg around town.

rpmrollbar

yes definitely a problem, my 97 6 speed gets around 26-28 hwy like clock work. 18-20 around town.

Jeffwilson34

My 98 A4 with 3.15 rear gears averaged 32MPG from Knoxville TN to Daytona FL last year. Using the DIC and old fashion pen and paper calculations.

lionelhutz

Is the car stock or not? You answer was confusing.

Are you using the display or did you calculate the fuel economy based on mileage and fuel pumped into the tank?


There are lots of hyper milers who would argue that cruise is not the most efficient way to drive, especially using cruise in hilly areas. Also, how did 70mph become the magic number to getting the best mileage? Typically, slower speeds like 50mph or 55mph yields better mileage. The first recommendation for increasing fuel mileage is to slow down to the posted speed limit or below.

Kreeess

hmm i get about 18-20 city and 24-27 hwy with a full exhaust and cam 6sp helps a lot

95rtturbo

Is your car a 6 speed? Not trying to ask a dumb question, but, if so, do you use 6th gear on the highway? That would definitely affect your gas mileage.

Also, cold weather combined with winter gas, will lower your mileage a bit (although even so, you obviously should be getting over 20 on the highway).

Jeffwilson34

open highway my best mileage is between 70-90 MPH

Windows up and AC on. It does drop about 2 MPH windows down and top off.

Not stock but only bolt on mods

I have larger intake, Longtube headers, straight pipes back to quad tip borla, vararam, and custom tune. I also have the 3.15 gears

Plus my engine has over 300,000 miles so I doubt ot is as tight as it once was. Not sure if that would change the milage though

Bluesteve1

i have a 2004 auto with 3.15 gears and i',m ave 15.3 in town right now. A lot of stop and go traffic and 35-45MPH.

racebum

stock 02z, avg 17-18mpg {i live in a metro area}, gets as high as 28mpg highway if i reset and drive a few miles

AFR is spot on and the fuel trims hover near zero on a scan tool.

how you drive the car has a big impact on mpg. 13-14mpg in town isn't hard to get if you use a little more throttle

coia96vette

My 04 with 3.15 gears and auto gets 19 to 20 around town and 28 to 32 on the highway when I keep my foot out of it. Quite a bit less when I want to have some fun with it.

lionelhutz

I can do much better at around 40mph compared to 60-70mph. Upwards of 50mpg....

QCVette

I have never tried 6th gear at 40mph, but at 55-60 mph mine does better than faster speeds. On mine it looks like if is not lugging the motor, the slower the better mileage.

Bill Curlee

You really need to determine and post if your engine is STOCK OEM or has modified parts on it. i.e. Headers, aftermarket air filter, Aftermarket Cam,, etc etc.

If it does, you need professional tuning. If it doesnt, you need to examine and replace as necessary the:

Air filter
Plugs
Wires
fuel filter

You could also have issues with the O2 Sensors.

AND

Data Log the PCM to figiure out what your long term fuel trims are doing. That will also let you look at the O2 sensor output to see if they are properly toggling HIGHT ot LOW, LOW to HIGH~~~~~

You also need to read and post your DTCs. Learn how to do it as it is very easy and VERY helpful when figuring out what is wrong with your engine/car:

READING YOUR Engine Diagnostic Codes



The Diagnostic Display Mode is entered with the following procedure:

1) Turn on the ignition but don't start the engine. NOTE! You can read the DTCs with the engine running and or driving down the road but it can distract you. BE careful! Some DTCs clear themselves when you turn the ignition OFF!

2) Press the RESET button to turn off any warning messages. (i.e. door open, trunk open ect)
3) Press and hold OPTIONS
4) While holding OPTIONS, press FUEL four times within a 10-second period.


Initially, on-board diagnostics go into an Automatic Mode which shows diagnostic codes in a pre-set sequence: PCM - TCS - RTD - BCM - IPC - RADIO - HVAC - LDCM - RDCM - SCM - RFA. All codes will be displayed for each. ( i.e. PCM = 4 codes) If none are present in a given module, you will see No More Codes on the display.
There are two kinds of diagnostic codes, Current and History designated with a letter suffix, “C” or “H”. A current C code indicates a malfunction is present and active in the module displaying data. A history code indicates a problem existed sometime in the last 40 or 50 ignition cycles. When not accompanied by a current code of the same number, it's potential evidence of a previous problem, now resolved, that was not removed by clearing the codes.
More likely it's an indication of an intermittent malfunction.
Intermittent codes are the most challenging of the diagnostics. An intermittent code may have happened once, may have happened more than once but is inconsistent or may be happening on a regular basis but not at the time the codes are displayed. History codes can also be caused by a current malfunction in a system that is not operating at the time codes are displayed. An example is the rear window defogger which doesn't operate until the Body Control Module detects engine rpm. For history codes set by a module that does not operate with the key on and engine off, a special diagnostic tool called a Scan Tester is necessary to properly diagnose the malfunction.
Once the system has displayed all modules, it goes into the manual mode which allows selection of each module using combinations of Driver Information Center buttons. Manual mode can also be entered during the automatic sequence by pressing any button except English/Metric (E/M). Once the display shows Manual Diagnostics, select a module by pressing the OPTIONS button to go forward or the TRIP button to go back. Once a module is selected, a code is displayed, and if more than one are present; press GAGES to go forward or FUEL to go back.
To exit the diagnostic mode at any time, press E/M. If you want to erase codes in a given module, press and hold the RESET button To reset the codes once in manual mode, press and hold RESET until it displays NO CODES Press OPTIONS to go to the next module. Repeat the steps until you have reset the codes in all the computer modules.
NOTE!! Only reset the codes IF you want to - it is NOT necessary to do this. Clearing a code does not repair a problem. You are simply erasing the evidence of it in the module's memory. If you clear the code/s, and extinguish the Check Engine Light, your emissions status ready will NOT allow you to pass an emissions test until you have completed the required driving cycles.
Once you have the codes, the next question is: What to do with the information?
First, consult the factory service manual. Any serious C5 Do-It-Yourself owner should invest in the Corvette Service Manual of the appropriate model year. The Service Manual is really a requirement if you want to understand and work on your C5. You can GOOGLE the DTC and also find information on it.




Here is very good site that explains the DTCs:


http://www.corvette-web-central.com/C5DTCcode.html


http://www.obd-codes.com/trouble_cod...d-ii-codes.php



Make sure to include the H or C suffix!!