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Posted

I reset my trip odometer and tank and trip mpg settings, and refilled my tank to full. Drove it 398.1 miles and filled it up today. It took 17.829 gallons. Comes to 22.3mpg. My ECU tells me that total mpg for the tank at fillup was 24.9mpg. Why the difference, and which is correct?

Posted

As long as your calculation of the amount of fuel that you used is correct, yours is invariably correct. INVARIABLY.

Posted

As long as your calculation of the amount of fuel that you used is correct, yours is invariably correct. INVARIABLY.

Well just a what if...

It does not take much more or less gas to change your MPG by 1MPG or more...what if you parked at a slant or maybe you topped the car off more, or the gas pump had a different shut off mechanism.

Knowing the amount of fuel that you used is the key to the above statement. The ways that I have just described could cause your car to hold more/less gas. I am not saying that the Computer is 100%. But the only way doing it by hand is 100% is to make sure you have your car filled up completely. A difference of 1 gallon can make a difference of +/-1.3 mpg...!!!

Posted

I reset my trip odometer and tank and trip mpg settings, and refilled my tank to full. Drove it 398.1 miles and filled it up today. It took 17.829 gallons. Comes to 22.3mpg. My ECU tells me that total mpg for the tank at fillup was 24.9mpg. Why the difference, and which is correct?

Sometimes certain pumps will not allow you to top off your vehicle as I noticed at a Sunoco yesterday with new pumps. I tried to top it off and the pump kept stopping like it was to the tee. Also, did you drive your car until it cut off. That's the only sure way you know that you used every drop of fuel to get an acurate percentage.

Also, I assume you were driving your 1998 version with the display. If I'm not mistaken, that tank can hold 21.5 gallons.

Posted

I reset my trip odometer and tank and trip mpg settings, and refilled my tank to full. Drove it 398.1 miles and filled it up today. It took 17.829 gallons. Comes to 22.3mpg. My ECU tells me that total mpg for the tank at fillup was 24.9mpg. Why the difference, and which is correct?

Why would you assume the gas pump at the station was/is correct?

Posted

Yes, it's quite possible that the pump at the station wasn't calibrated, as Lexirx330 mentioned, with a different shut-off mechanism, that shut off at a different time than before. I did use the same service station, but I might have been at a different pump. I don't top off, so I can see where it's possible that the pump stops but didn't fill it to the same level as before. Oohryry - yes, this is for my '98. I'd love to know exactly how accurate the ECU is, how it works, and what the margin of error is. But I can now understand that the pump is probably what's inaccurate. Hey not bad...24.9mpg average city/highway, A/C on constantly, 233k miles. :D

  • 1 year later...

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