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Old 10-28-2013, 05:16 PM
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EVIC vs Calculated MPG

I have been resetting one of the EVIC trip computers when I fill up and also tracking mileage with a MPG calculator app. I'm pretty disappointed the EVIC seems to be 10% high in the estimation. My last fill was the worst with the EVIC saying 19.9MPG for the tank and the calculation giving me 17.89. I realize there is some variation in fill-ups, but generally I fill up at the same costco. Are you guys seeing similar discrepancies? There was an article in C&D on this same topic. I think this is pretty common, but you would think the trip computers would account for ethanol in the fuel since most states require it.
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Old 10-28-2013, 05:20 PM
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Re: EVIC vs Calculated MPG

I have seen discrepancies but when i tried to voice that out I was shot down by people saying EVIC is pretty acurate and that MPG calculations varies on type of gas, driving habits and so on, so I am just living with what i got. Glad to see that once again I am not alone on this.
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Old 10-28-2013, 05:28 PM
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Re: EVIC vs Calculated MPG

Unless you top off the tank every time, which for some reason is not recommended, there can be quite a big difference in how full your tank is.

What mileage you are getting isn't as important as seeing it drop, either suddenly, or over time. I say if you want to check your mileage, pick a method and stick to it.

I use the EVIC and take a look at it every couple of months. If it varies from tankful to tankful, so what. Unless you plan to tear your engine apart to look for that extra half mile per gallon, mileage is like pro football scores. You have nothing to do with them, can't change them, but can talk about them into hell freezes over.


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Old 10-28-2013, 05:52 PM
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Re: EVIC vs Calculated MPG

Mine has been very close.
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Old 10-28-2013, 07:57 PM
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Re: EVIC vs Calculated MPG

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Originally Posted by bill_de View Post
Unless you top off the tank every time, which for some reason is not recommended, there can be quite a big difference in how full your tank is.

What mileage you are getting isn't as important as seeing it drop, either suddenly, or over time. I say if you want to check your mileage, pick a method and stick to it.

I use the EVIC and take a look at it every couple of months. If it varies from tankful to tankful, so what. Unless you plan to tear your engine apart to look for that extra half mile per gallon, mileage is like pro football scores. You have nothing to do with them, can't change them, but can talk about them into hell freezes over.


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Exactly. Just like any gauge. You calibrate in your mind what is "Normal". And go from there.

As long as it's consistent.
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Old 10-29-2013, 08:38 AM
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Re: EVIC vs Calculated MPG

Consistent filling of the tank (which is difficult to do without topping off) is the key to an accurate measurement. On all my vehicles the "EVIC" has always been optimistic by about 1 mpg compared to an actual measurement. Topping off is not recommended because it can overwhelm the EVAP vapor recovery system, but it's about the only way to really get a consistent measurement.
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Old 10-29-2013, 09:23 AM
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Re: EVIC vs Calculated MPG

I almost think that the EVIC is a running calculation of the last X number of miles (or something) vs. a calculation from the time the trip computer was reset. I use an app to track mileage and it was always spot on with what my Acura read but tends to be just a little lower than what the EVIC says in most cases on the Jeep.

I remember in my old Saab it use to show average MPG over the last 30 or so minutes of driving vs. the last tank of gas.
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Old 10-29-2013, 12:01 PM
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Re: EVIC vs Calculated MPG

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Originally Posted by TurboRush View Post
I almost think that the EVIC is a running calculation of the last X number of miles (or something) vs. a calculation from the time the trip computer was reset. I use an app to track mileage and it was always spot on with what my Acura read but tends to be just a little lower than what the EVIC says in most cases on the Jeep.

I remember in my old Saab it use to show average MPG over the last 30 or so minutes of driving vs. the last tank of gas.
No. It starts at 0 after a reset of the trip odometer.

My trip 2 which was never reset almost matches the mpg on the economy gauge. The latter was reset to 0 when they replaced the PCM.


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Old 10-29-2013, 12:45 PM
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Re: EVIC vs Calculated MPG

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Originally Posted by bill_de View Post
No. It starts at 0 after a reset of the trip odometer.

My trip 2 which was never reset almost matches the mpg on the economy gauge. The latter was reset to 0 when they replaced the PCM.

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Old 10-29-2013, 02:31 PM
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Re: EVIC vs Calculated MPG

Just for the hell of it I have been keeping track of my calculated MPG and EVIC reading since I purchased my JGC in August. The largest delta was 1.5 and smallest was .10. The EVIC reading has always been the higher number.
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Old 10-29-2013, 02:47 PM
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Re: EVIC vs Calculated MPG

Wasn't there a class action lawsuit against Honda for something like that where the mileage the vehicle computer was saying the car was getting in regards to what it really was acheiving? Honda lost the case if I remember right.
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Old 10-29-2013, 03:29 PM
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Re: EVIC vs Calculated MPG

I know my Subaru is calculated off of fuel injector duty cycle and what it believes the flow is for the fuel injectors.

When I replaced them with larger injectors (~550 to 1000) it made my MPGs go from .5-1.5 high to about 10 MPG higher than actual. I just use Fuelly and track my MPGs with trip miles versus gallons into the tank. The MPGs in the car just give me a guesstimate of where I am at.
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