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Discussion Starter · #1 ·
Okay so I recently got a new exhaust on my 2013 Honda Civic EX (yesterday). My gas ran out so I filled it up with gas. My Trip is set so that whenever I get gas, my TRIP A would be reseted. So here's where the problem comes along... I drove around and got 10miles on trip A, and my MPG is 30mpg but Im noticing that the mpg on the iMid screen is dropping point per point and eventually dropped to 28.9 even though my car is just turned on (not even on drive). So I switched the Trip to B which has 200 miles already. It's listed as 27.1 MPG because of my old stacked up miles, but the weird thing is that the mpg on the iMid on trip B isn't dropping point per point like the one on Trip A?

What should I do!? This ishh.. is pissing me off!

Is this the computer wrong calibration or is my exhaust eating up my gas on idle?
 

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Discussion Starter · #2 ·
My old stock exhaust didn't drop my MPG on the imid when the car is on idle. But with my new exhaust it started dropping my mpg by .2 or so every 5 seconds or so. (Only on trip A - which currently has 7 miles). But the weird part is it doesn't drop my mpg on trip b imid (has 200miles)
 

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it also factors in how long your car sits idling and because you have that new exhaust you are moving more air through the engine (even if you don't have an after market intake you are still moving more air and your ecu can see that and is trying to compensate by adding more fuel. so now it can see more fuel being used at a faster rate than before and is giving you lower mpg ratings. a vit tune would probably fix this issue if the R18's had flashpro. but until then there isn't really anything you can do.
 

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no it's not eating a lot just a little more than it would with factory parts. to but i would just reset all trips and start from scratch. it's kinda like jliu said. your car is used to seeing a constant number but now it's seeing a lower number and re-adjusting the average. trust me it will be fine. any car with low mileage trips like yours is gonna show major changes because there isn't a lot of mileage to base it's average off of. trust me.when i reset my trips on my si and I get heavy on the gas it drastically drops my average I've seen it drop by up to 8mpg before. If you are easy on the throttle you'll be fine but the more after market parts you put on without tuning the more it will kill your mpg regardless of being easy on the throttle or not. after you get a few thousand miles on the trip meters it will be harder to drop your average.
 

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Discussion Starter · #6 ·
But it drops by .2 on idle every 5-10 seconds when low miles on trip. But it never did this with old stock exhaust. By how much lower do you think it will lower the avg mpg? It hurts seeing the drops
 

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But it drops by .2 on idle every 5-10 seconds when low miles on trip. But it never did this with old stock exhaust. By how much lower do you think it will lower the avg mpg? It hurts seeing the drops
yup my Si did it on idle as well but I just ignore it and drive lol I only pay attention to how much distance I have left on the tank =P I drive mine about 80-100 miles a day so all I know is eventually I WILL have to put gas in it if i wanna keep driving lol mpgs don't matter to me as much as they used to I just drive the absolute $#!T out of my car lol and surprisingly I still get decent gas mileage lol I've got about 240-280 miles on this tank so far and it's only half empty so I'm okay with those kind of numbers lol as long as it's not like 240 miles to the tank then I'm alright with it =P
 

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Not sure I trust the i-Mid readout... A couple of weeks ago, I did a "lap" around I-465 here in Indianapolis in the middle of the night. I set the cruise to 60 mph, windows up, A/C off, ECON off, pulled my feet back and just steered the car for 52.3 miles. The mpg readout for that little trip was 43.9. Really?

P.S. 2013 Civic LX sedan 5-speed manual everything stock...
 

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This really has nothing to do with your exhaust, unless you bought a bad one but I doubt you did. It's more of your car doing average MPG calculation after reset. If you use 1 gallon for 30 miles, then you would get 30MPG. But after 30miles, you car just idle and do nothing until your tank is empty. You would have used 12 gallons in 30 miles. That's 2.5 MPG. Do you expect your car not to use gas when it's on idle?

As for trip B, if you stacked up 9000 miles in 300 gallons, then you have 30MPG. And if you filled full tank and let the car idled till it's empty, then you have 9000 miles in 312 gallons. You would get 28.8MPG. See the difference?
 

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When idling you are getting 0 mpg with or without the stock parts.... averagingn0 into anything will ruin ur average... if u only havena few miles on one trip of course it will change faster than another trip meter with way more miles.. simple math dude. Sry to say.
 

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well yeah like everyone else, you have only driven 10 miles on trip A and you said there is roughly 200 miles on trip B, so a 0 MPG at idle is going to affect a 7 mile trip a whole lot more than a 200 mile trip, remember in school figuring out grades? if you have 3 tests of 100, 85, and 60 your test average is 81.67 but factor a 0 in as a 4th test now that average drops to 61.25, but replace that 0 with a 50 then your average is 73.75.
like TheTech said sorry but its simple math.
Besides why are you sitting at an idle just staring at your MPG?? do me a favor reset B and just drive 1000 miles then check your MPG on trip B, I guarantee, you wont be disappointed. you cant drive 10 miles and expect to see huge numbers, just doesn't work like that.
When I bought my SI it had 35 miles on it, MPG was at 19, ive now added 650 miles to trip A and watched it rise from 19 to 26.5 so yeah, just drive a 1000 miles without looking at that screen, you'll see the difference.
Don't be one of those MPG retards that freaks out over MPG, you bought an econo box, that on average gets 25-35 depending on driving style.
just drive dude, it will work itself out, besides these EPA estimated MPG numbers are developed going downhill with the wind and a 100 pound midget behind the wheel, at 50 MPH, most highways in the US are 65 or better, hell Texas is 70-75 on most and even has some at 80.
 
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Discussion Starter · #13 ·
Thanks guys but back then with my old exhaust, I can leave it on idle and my mpg would never drop thy fast. With my new it drops like .2 every 5 seconds so it hurts seeing that drop. (It's an r18)
 

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When idling you are getting 0 mpg with or without the stock parts.... averagingn0 into anything will ruin ur average... if u only havena few miles on one trip of course it will change faster than another trip meter with way more miles.. simple math dude. Sry to say.
If the OP reset trip a & b at the same time. His "problem" would be solved.
People stop over thinking everything.

What matters, here, is how many miles the car can travel on a tank of fuel.
 

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this is being way over thought. bstone got it right on the head. got 200 miles worth of MPG data on one trip.. and only a few miles on another trip, averaging in 0 mpg to both would affect the trip with lower miles much more. if you get up to 50+ mpg. reset your trip meter while coasting all the way down to an almost dead stop.. look at your mpg. you will have an unreaslistically high mpg rating.. reset it while at a stop, and just sit there n it will stay at 0. if you have a couple miles on a trip it will increase or decrease much more readily because it has less data to average it with. the Grade book reference was a good one. if you are at a 95 at the end of a semester, you can bomb that last test and only lost a few percent.. if you are a week in, and only have a couple grades enteres, you bomb a test and your grade is F'd. end of thread. just relax, reset that trip meter, drive lightly for a while and be happy with your average. i dont mean any of this in a rude way, sorry if it sounds like that. cant think of another way to explain it.
 

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More simply, it's all about averaging.

The more data you have, the harder it is to introduce new data to change the old data.

Let's say you have room with a very small number of people. It's going to be much easier to move them around than if the room was full of people. It's the samer thing with th empg numbers. They will be affected more at the beginning of the calculation cycle on Trip A right after a fill-up than after many miles.

Trip B, which is never normally reset, is working with a huge number of averaged calculations and is very hard to budge. as mentioned above, reset A and B at your next fill-up and watch how they coincide.
 

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law of averages..if you threw in an outlier to a big set of numbers, it wouldn't influence the average much. exactly what i've been saying..
 

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If you were to put a gallon of gas in a civic turn it on and let it run till it dies. You won't get 30 mpgs you get 0 cause you haven't gone anywhere.. so if it was reset and your just chilling at the gas station it will go down.. gas is still being fed to the motor so gas is being used...hope that made sense

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