Horrible MPG (was getting 37 mpg, now 27)

Hi, I own a 2015 es auto Mirage. Bought it almost new at 5 k miles. until 46 k miles I always average above 37 mpg.
Now the best I can get is 27 mpg. I changed, oil every 5k with mobile one full Synthetic. New air filter, New brakes, " made sure they where not the the problem" use good quality gas, not the problem. Not hard on the car. nothing has changed since I owned it a long time, same style driving. When the issue started thought maybe spark plugs, changed them didn't change. change air filter didn't matter, checked tires brakes, gas no fuel leaks... asked Mitsubishi they have no clue, asked my uncle a retired master mechanic he has no clue. Seriously Im lost. Anyone have any deep insite. No engine lights shifts fine. I also check my mpg manual each fill up and it correlates to the cars readings, so that is not the problem. Any Ideas? seems to run great just mpg is horrible for this car!

Have Mitsubishi or your uncle inspected the car? If not, I think that it would be in your best interest. It may be your oxygen sensors that have gone bad. Have you done any modifications to your car?

Ignore my post on your other thread... looks like you did all the obvious checks. I can't say I've ran into that problem yet. My work has almost 40 mirage's and the worst mpg I've seen on the display is 39mpg shown on trip "B".

check compression in all 3 cylinders.
From experience I know these cars run quite well with little to no compression in one cylinder. They just get hard to start in cold weather.

Someone with a very good scan tool (not a $59 code reader) needs to take a look at some basic diagnostic data in your car's computer. I would want to know what your car's long and short term fuel trim looks like. Without going into a huge explanation, it's a simple way to tell if your computer is intentionally directing more fuel to be burned by the engine for some reason...like to compensate for a real or perceived lean condition caused by too much air entering the engine.

Here's a quick overview: Fuel trim can be a valuable diagnostic tool

Any chance running higher ethanol fuel content, the drop matches up with my experiments/experience with other cars, FFV and non. The LTFT will be +20-30 even with E50. 26-28 throws a CEL on my non-ffv cars (<55% ethanol).

My wife filled her fairly new to her 2015 rogue a while back with a full tank of E85 (previous 2 cars were FFV). Next day when I drove it I noticed it didn't start a quick as normal instantaneous. Little while later notice a small CEL, 10 miles later I figured out what she did, dropped from 33 with me driving it to 25. We were doing a little road trip that day, so I just kept topping off and the CEL cleared the next night. I've blended in all my car, up to E50 usually no symptoms at all(other than some loss of mpg), other than the start the rogue didn't mind E85, but I tried not to work it very hard.

I use the same gas stations as my 2013 scion Tc which gets 28 mpg, and i drive it hard. so I dont think that is the issue. Yes I agree maybe a better diagnostic tool should be used. My harbor freight one reads nothing as I have no codes anyways. I did call Mitsubishi in Plano and they had no Clue, anyone maybe have suggestions for someone in the Dallas area. Its worth it for me to pay a little to figure it out as currently my simple things have all been done and still with the horrible MPG. BTW I did try 91 for to tanks and no difference made. this has been going on since 46k miles im almost at 50k. done everything I know so far. I might try a independent shop, this Mitsubishi im plano just told me , plugs, air filter, gas, oil, tune up, tires, brakes.... ive done all those! My uncles tools are outdated been retired 5 years....sorry if my english is bad I try. I will have my uncle check compression also. thanks for the ideas. I will update tomorrow my uncle said he can check compression in the morning, and have another app at Mitsubishi in Dallas.

Even something simple like a bad coolant temperature sensor can lower your fuel mileage...

Symptoms of a Bad or Failing Coolant Temperature Sensor

Again...this is something that won't necessarily cause a check-engine light, but it will be obvious to someone with a good scan tool.

Hello ivsito and welcome to the forum.

Hopefully you are able to figure this out soon. The first thing I thought of was fouled valves, as in this thread: 3A90 Intake valves stuck open, carbonized, full of gunk and car won't start. I expect this would lead to poor compression as IchabodCrane suggested.

Whatever the cause, please be sure to share your findings.

Please do, I've been in a similar situation all year. I luckily still have to do a lot of highway driving where it still shines, but city mpg is deplorable.

Quote:

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Originally Posted by Spadesheart

Please do, I've been in a similar situation all year. I luckily still have to do a lot of highway driving where it still shines, but city mpg is deplorable.

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By the way, what kind of engine oil are you using? ivsito mentioned he uses Mobil 1.

Quote:

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Originally Posted by ivsito

I changed, oil every 5k with mobile one full Synthetic.

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Quote:

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Originally Posted by Top_Fuel

Someone with a very good scan tool (not a $59 code reader) needs to take a look at some basic diagnostic data in your car's computer. I would want to know what your car's long and short term fuel trim looks like. Without going into a huge explanation, it's a simple way to tell if your computer is intentionally directing more fuel to be burned by the engine for some reason...like to compensate for a real or perceived lean condition caused by too much air entering the engine.

Here's a quick overview: Fuel trim can be a valuable diagnostic tool

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https://www.amazon.com/dp/B01NCEXGXF wonder if this might work. Seems to be able to show live data.

http://mirageforum.com/forum/showthr...-5-spd-and-CVT

Compare your steady speed MPG to the speed/mpg chart just to make sure something out is of whack. I know the longer I own a car/motorcycle the more rpms I tend to use. 50 mph should net close 60 mpg.

If you've replaced your tire recently that can have a big negative on MPG.

Quote:

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Originally Posted by Eggman

By the way, what kind of engine oil are you using? ivsito mentioned he uses Mobil 1.

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I'm using the 0w20 variant of Motomaster Formula 1. I bought 3 5 L jugs in Canada for very cheap (26 CAD each) to use for 5 oil changes. I believe I have done 4 now. I am not changing at such short intervals though, rather opting for the amount they say I should be able to get. perhaps I should change it more regularly; it really isn't a lot of oil per change.

http://www.canadiantire.ca/en/pdp/mo...-0288712p.html

Any more news to report, ivsito?

Just reading up on threads.

Check this out..

https://mirageforum.com/forum/showth...v-then-normal?

You've got to be kidding me. Are you just a spammer kid?

No sir, just trying to help :)

I was starting to get irritated since I just bought the car and haven't seen anywhere near the 44mpg advertised. It's the main reason I bought the car. So far though it's a pretty decent ride and I don't understand all the hate I've seen in more than a few reviews.

Kungpaoshizi,welcome to the site.

I've seen you've replied to a lot of the fuel economy threads. I think you should start your own thread, otherwise it's going to be too messy for people to help you figure out what might be going on with your car's fuel economy.

Also, so we know what year/trim/transmission you have (and then that info will be linked from all your posts), make a garage entry: add car

Ahh forgot to add to the garage, thanks for the reminder.

That thread I linked I guess you could call my main thread on this. After reading through abunch of posts in this section it sounds like there's a few other people in the same boat. Whether or not they're related will be the big mystery.

After I got into cars when I got a miata I found out they're about as complex as computer systems in corporate environments. :)
I found a new respect for mechanics at that point in my life!

I got 28mpg from a single rear tire losing air slowly from a nail. I was really stunned how much tire psi matters for mpg

My advice might not be worth anything, but it's free:

-- I keep tires 2-3 psi higher than recommended.

-- To the OP and others getting crappy mileage, do you live where it is hilly? A steep hill can make mpgs plummet at least temporarily. A lot of hills will lower the average.

-- Do you have, and if so are you using, cruise control? I've read reports from tests that show people getting worse fuel economy using cruise control, unless they are using it almost exclusively to maintain speed on long, flat stretches of highway.

-- If you are avoiding burning up fuel needlessly with jack rabbit starts and fast acceleration, remember that you are also wasting gas if you are hard on the brakes. Try slowing for stops and turns much earlier, with foot off of the gas and occasional light braking, so that much less brake is needed when you get to finally get to the stop or turn.

-- Leave earlier and travel more slowly.

If I were getting mpg in the 20s on my 2015 DE, I'd also check any of the mechanical issues--sensors, etc.--others have mentioned if they haven't all been checked yet.

That's all I got.

I averaged 32mpg on my first fill up after buying my car a couple weeks ago. Very frustrating. I'm not hard on the gas. And my drive to work is only 9miles, 6 of which is hwy.

2015 RF 67k.

How fast on the hwy? How much stop & crawl?

Which transmission? (Make a garage entry: add car)

What were you getting from your previous car on the same route, and what car was it?

I live in a very hilly area ( the alps in europe ) and drive mostly to work and back.
42 Kilometers ( 26 miles ) a day. City driving to work, Highway home ( 125 kmh ( 78 mph ) average Highway Speed ).

My Attrage ( G4 ) gets 95 or 100 octane Gas, and gets 43 mpg ( 5,5 l/100km ).

On some days of the Week, the Highway is limited to 100 kmh ( 60 mph ) because of environmental Protection.
On these days my computer says that my Attrage only nips 4,7 L/100km ( 50 mpg ).