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Discussion Starter · #1 ·
About 4 weeks ago I hit a deer, I took it to a highly recommended body shop to get some work done and they replaced my bumper and it looks great. However, now that I just got my car back my MPG seems to be like super sensitive. Before I was getting 27.1 and when I would get on it for awile(riding high rpms) it would drop to like 27.0 or 26.9 after an hour or so. Now my MPG is at 25.7 and if I hit the throttle to accelerate up a hill it’ll drop to like 24.9 in a matter of seconds. Is this normal? I didn’t know if maybe something couldve been unhooked during Maintenance or reset somehow. Thanks.
 

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How are you calculating MPG? Are you just using the car's output for MPG? If yes, how often were you resetting it when you saw 27, every tank or was that over several fill ups? Does WV switch to winter gas? As the temps drop, so do the mpg's.

Best is to track it the old fashion way at each fill up and then you can see what your average is and how it compares.
 

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Discussion Starter · #3 ·
I was resetting MPG for every fill up. Another thing I noticed is that when my car idles. The Average MPG that displays on the bottom left of the four way screen is on 0.0. I’m not sure if it’s just me but I thought before when it idled it would stay and 99.9. Until I gave it gas. But like I said, it may just be me. Thank you for your help btw I appreciate it!
 

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Technically the MPG is supposed to drop pretty quick if you per-say reset your mileage and then put 40 miles on your car and floor it. Vs if you haven't reset it in a long time and you have 300 miles on the MPG calculator and you floor it...it'll hardly move. Mine is terrible at all times, but I doubt the deer would have caused any problems like this.
 

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Discussion Starter · #5 ·
I agree, I was just unsure if the MPG went off your trip miles or to ODO miles. I’ve only had the car 11 months and it only has 9k miles. However before I sent it in the shop, I did reset my miles on Trip 1(like always) and I also reset my mile on Trip 2, which I haven’t done since I bought the car. So it had like 9k on the trip. Which maybe explains why the MPG was never sensitive before? Thanks for your help btw!
 

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I don't reset the MPG counter, I just rest the trip. Mine is sitting at 25.1 if I remember right. Last time I rest the MPG counter it started around 28 and has fallen to where it is now. But mine is usually reads low after it's not been reset for a while.

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Has the air temp been dropping where you live? Colder air is denser and the computer is going to add the appropriate amount of fuel (more) to make the proper ratio. You will also build more power earlier until the computer starts to pull fuel and timing as you reach the torque target. My mileage usually drops 10 - 15% in the winter.
 

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If you are getting 24 or 27 while driving mainly city, you're doing well! I have noticed that my average MPG (calculated, not based on the computer) with about 60-40 city/highway is 28.36 mpg on 42,00 miles of driving. If i'm only doing city driving (speeds up to 45mph, for 20 min or less drive time per trip), i usually get in between 24.5 and 26.5. Highway, I'll get 31ish.

Your real time MPGs will drop to 0.00 on your computer when you aren't moving. You're consuming gas, but you're not moving or adding miles. It has never shown 99.9, so i think you may be mis-remembering.

Honestly, everything sounds fine. I don't think your deer accident effected anything. :)
 

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I think everyone has got you covered here but I will also add my experience.

I was getting 31 all summer. temps dropped and Oregon winter gas and I am getting around 28 now. only two factors that changed.

Hitting a deer cant cause MPG change as long as they didn't make a drastic change to your car when putting it back together, it would really have to be a major change, simply aero isn't going to make as big of change as much as air or fuel.
 

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The active mpg square in the cluster will display will say 99.9 mpg when I am downshifting and letting the engine slow the car. Cold weather will hurt mpg a lot like stated above. Also, I recently took my active grill shutters off. I noticed a half to full mile per gallon drop in my overall computer mpg. Maybe they didn’t hook that back up or it’s faulty?


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The active mpg square in the cluster will display will say 99.9 mpg when I am downshifting and letting the engine slow the car. Cold weather will hurt mpg a lot like stated above. Also, I recently took my active grill shutters off. I noticed a half to full mile per gallon drop in my overall computer mpg. Maybe they didn’t hook that back up or it’s faulty?


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Yeah you can get it to say 99.9 if your car turns "off" the injectors in situations such as coasting down a hill at 60mph. The car's Air/Fuel ratio will go from the normal 14.7 cruising to like 44.9 and it hardly uses fuel but is moving 60mph.
 

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That’s perfectly fine. It was previously stated that “it has never shown 99.9”- by AcAciA1153. I was telling how it shows 99.9 for me and that’s coasting off throttle in gear.


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All modern cars have Deceleration Fuel Cut Off. DFCO completely shuts off the fuel injectors when coasting at zero throttle in gear (and certain other parameters are met). Probably DFCO has kicked on whenever you see the instant MPG display showing 99.9MPG. If you switch the quad display to metric it will instead show liters of fuel consumed per 100 kilometers distance. Using this metric you can see the value drop to zero fuel use when DFCO kicks on, as when rolling down a hill at 0% throttle.

Do any of the aftermarket tunes disable DFCO? That could result in never seeing the 99.9MPG value.
 

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All modern cars have Deceleration Fuel Cut Off. DFCO completely shuts off the fuel injectors when coasting at zero throttle in gear (and certain other parameters are met). Probably DFCO has kicked on whenever you see the instant MPG display showing 99.9MPG. If you switch the quad display to metric it will instead show liters of fuel consumed per 100 kilometers distance. Using this metric you can see the value drop to zero fuel use when DFCO kicks on, as when rolling down a hill at 0% throttle.

Do any of the aftermarket tunes disable DFCO? That could result in never seeing the 99.9MPG value.
No aftermarket tunes disable it, BUT guess what does? Cruise control. On cruise it will never ever "let off the gas" even downhill. Using a light foot will always beat cruise control in MPG for this reason. Plus, I've had my cruise spike to like 20psi once hitting an uphill...no thanks because I was in 5th or 6th :lol:
 

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That’s perfectly fine. It was previously stated that “it has never shown 99.9”- by AcAciA1153. I was telling how it shows 99.9 for me and that’s coasting off throttle in gear.


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You seem to have missed the very obvious qualifier to my statement. I said "When you aren't moving". The OP was talking about a 99.9mpg reading "while at idle" indicating his vehicle was not moving.

As the previous people have said. You're engine will read 99.9+ mpg while coasting to a stop IN GEAR due to your injectors being shut off and car being in motion (your car is gaining mileage and using 0 fuel)
 

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I've had my cruise spike to like 20psi once hitting an uphill...no thanks because I was in 5th or 6th :lol:
thats the problem with cruise control with a manual, the car can down shift when needed, with a manual all the car can do is throw as much throttle at it as it can to try to keep up to the speed selected.
 
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