How accurate?

[CharlesBrown]

Ever checked the accuracy of the panel gauge that indicates avg. & inst MPG. I think mine lies!

 

[gmjunkie]

Ever checked the accuracy of the panel gauge that indicates avg. & inst MPG. I think mine lies!

I don't know about a C4,but my C5 is purdy darn close!!!!!! I've checked it on paper on short trips and on long trips, it has been always within a tenth or two!!

 

[LT4man]

My 96 seems to be right on the dot! Of course, mine is a bit newer than yours.

My 93 Grand Prix seems to be pretty darn accurate, too!

SAVE THE WAVE!

 

[OldCorvetteFan]

Ever checked the accuracy of the panel gauge that indicates avg. & inst MPG. I think mine lies!

When I compare the car's indicated mileage to the actual, it's been very close (within a few tenths).

I don't know of a way to verify the instantaneous readout - how are you doing it?

Steven

 

[G Winter]

All of my GM cars have been very accurate up to my vette. My instant and average are both off by 4 mpg . This does not vary I can count on if the average says 30 I am getting 26 mpg. It is intresting that my tach also reads high but not real sure how much, guessing about 10% maybe even 15% I have been wondering if this is related. The speedometor seems to be right on.

Glenn

 

[Vettefan87]

If you reset the Average every time you fill up it is pretty accurate.
​

 

[OldCorvetteFan]

All of my GM cars have been very accurate up to my vette. My instant and average are both off by 4 mpg . This does not vary I can count on if the average says 30 I am getting 26 mpg. It is intresting that my tach also reads high but not real sure how much, guessing about 10% maybe even 15% I have been wondering if this is related. The speedometor seems to be right on.

Glenn

How are you determining that your instantaneous mileage is incorrect?

Thanks,
Steven

 

[DRTH VTR]

How are you determining that your instantaneous mileage is incorrect?

Thanks,
Steven

You can't. Short of some fairly sophisticated devices, I don't see how to do it. You still see cars that estimate it from maniford vacuum. My wife's BMW looks like it works that way.

The system needs to know two things to derive fuel mileage: amount of fuel used and distance traveled. The distance is easy. The speedometer, odometer, etc already count distance. The input may be wheel rotations, driveshaft rotations, or some similar thing. But the computers already know distance. The fuel measurement is more tricky. It cannot use the gas guage, as that measurement is way too crude. I asked c4c5 how the car determines fuel use, and he said that it calculated it from fuel injector data. So it is a calculation, an estimate. It is not directly measured. It would be possible to directly measure fuel use, but that is not what is done in the Corvette.

 

[LlanoBill]

Both of my 96's are dead on as to average and very close on "range".

 

[G Winter]

My range is way off also. The instant never goes down near far enough on excelleration. I am comparing it to my other GM cars.Also on light load it also goes to unreasonable numbers.
Does the average milage calculation also use engine rpm? and does the ECM perform this calculation? If there is a fix for this I would like it to be right. I like to keep everything working right.

Glenn

 

[milehigreg]

Dead On

I checked it on a 2300 mile trip to Phoenix last October and it was dead on.

 

[larry bud]

Ever checked the accuracy of the panel gauge that indicates avg. & inst MPG. I think mine lies!

I've found that the more mods I do to the car, the farther off it goes. Mine will read 25 when I'm getting 17. That 50% wrong!

 

[G Winter]

I've found that the more mods I do to the car, the farther off it goes. Mine will read 25 when I'm getting 17. That 50% wrong!

I wonder if the incorrect ECM could cause this. I noticed my ECM is a rebuilt.

Glenn

 

[ben73]

The fuel consumed is calculated by summing all the milliseconds that the injectors are open. This makes the result very dependant on fuel pressure. If you have increased the fuel pressure, it will be getting more fuel/msec and the calc'd display will appear optimistic.. and vice versa..

 

[davec0_17]

All of my GM cars have been very accurate up to my vette. My instant and average are both off by 4 mpg . This does not vary I can count on if the average says 30 I am getting 26 mpg. It is intresting that my tach also reads high but not real sure how much, guessing about 10% maybe even 15% I have been wondering if this is related. The speedometor seems to be right on.

Glenn

How can you tell your tach is reading to high, and how you determine by how much?

 

[G Winter]

Using the speed in 4th gear the tire size and the gear ratio you can calculate what the rpm should be. Or you can figure what your speed should be at a given rpm.

Glenn

 

[WhalePirot]

How can you tell your tach is reading too high?

You could use a tach from a tune up device and compare the two.