How accurate is the MPG detector computer thing?
Senior Member
Joined: 08-06-2007
Posts: 359
From: Edison, NJ
The MPG calculated by the computer cannot be wrong, if the diameter of the tires is the same as came from the factory, and the fuel injectors have not been changed.
Each pulse of a fuel injector injects a precise amount of fuel into the combustion chamber. Each rotation of a wheel advances the vehicle a specific distance.
To determine how much fuel is consumed, the computer counts the number of times the injectors are pulsed and multiplies that figure by the injector's delivery volume per pulse. (there may be pulse duration factors in there somewhere)
Simultaneously, the odometer is counting the revolutions of the wheels, and determining how far the vehicle has traveled. Computers cannot be partially correct. They can only be correct, or non-functional.
The trouble is that engines spend a lot of time consuming fuel while the vehicle is at a standstill. However, since standing still is also a significant part of vehicle operation, you are getting the REAL MPG from the computer.
Each pulse of a fuel injector injects a precise amount of fuel into the combustion chamber. Each rotation of a wheel advances the vehicle a specific distance.
To determine how much fuel is consumed, the computer counts the number of times the injectors are pulsed and multiplies that figure by the injector's delivery volume per pulse. (there may be pulse duration factors in there somewhere)
Simultaneously, the odometer is counting the revolutions of the wheels, and determining how far the vehicle has traveled. Computers cannot be partially correct. They can only be correct, or non-functional.
The trouble is that engines spend a lot of time consuming fuel while the vehicle is at a standstill. However, since standing still is also a significant part of vehicle operation, you are getting the REAL MPG from the computer.
Moderator
Joined: 01-23-2009
Posts: 26,533
From: Fredericksburg,VA
Are the 60's cheaper than the 50's on the tires? I may have to check on that because I replace tires about every 6 to 8 months. I drive about 100,000 miles a year and I have an 09 ls with 227,000 miles right now. My speedometer is about 2 miles per hour slower than what my gps shows with the stock size tires.
I just got a photo speeding ticket the other day with the Cruise Control set at 66 MPH, the photo threshold is supposed to be 69 MPH in a construction zone in Maryland. The GPS was wandering around a bit 68 - 70, it was raining and going down hill. If you really want to, you can change the tire size with a Tech II scanner.
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Joined: 01-23-2009
Posts: 26,533
From: Fredericksburg,VA
Today I put 15.938 gallons in the tank, and it did not overflow! I happened to have the Owner Manual out at the same time and noticed that the capacity is actually 16.2, I could have made it the Costco, darn it.
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Joined: 09-15-2011
Posts: 90
From: Florida
Senior Member
Joined: 02-10-2011
Posts: 113
From: Temple, Ga
I put in 15 gallons even yesterday. I think it cost around $55.00 though. How much is the gas up there now? We are around $3.70 to $3.75 a gallon.
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Joined: 01-23-2009
Posts: 26,533
From: Fredericksburg,VA
Senior Member
Joined: 02-22-2012
Posts: 376
From: Baton Rouge
I filled mine up yesterday and the electronic gage said I was averaging 25.2 mpg but paper and pencil said 30.1mpg. I rechecked and 30.1 is correct. I suppose the average is over many tanks of fuel and the 30.1 is just for this one tank...that would make sense. The next time I check it I will zero the average when I start on a fresh tank and see how close the average is to paper and pencil.
Platinum Member
Joined: 12-06-2009
Posts: 11,721
From: Alabama
I filled mine up yesterday and the electronic gage said I was averaging 25.2 mpg but paper and pencil said 30.1mpg. I rechecked and 30.1 is correct. I suppose the average is over many tanks of fuel and the 30.1 is just for this one tank...that would make sense. The next time I check it I will zero the average when I start on a fresh tank and see how close the average is to paper and pencil.
Senior Member
Joined: 10-21-2008
Posts: 1,831
From: hemet, calif.
I have an 2006 2lt, mileage shows average MPG, always 17.6 around town or on the freeway 65- 75 MPH the average mpg stays pretty much the same as around town, the newer HHRs are more exact, can the computer be programed to show instant and average.???