My MPG seems very low for a mostly stock Honda, suggestions please?

[Dorachagi]

So I joined fuelly.com to start tracking my gas mileage in my 2005 Civic Si. Just finished my second fuel stop (must have two to start getting stats) and I averaged a dismal 18.8mpg over 107 miles. Out of 200 or so Si's on fuelly this is I think the second worst mpg of all. I have very few mods and a cold-air intake is the only one that would affect gas mileage. I drive pretty aggressively, but not constantly and I haven't been racing at all. The oil was changed recently, and when I get home today I'm going to check the air filter and spark plugs. Does anyone have any other suggestions? The average mpg for Civic Si's is in the high 20's, so could mine be this low solely due driving style or would you think this indicates a problem with my car? Thanks for any and all advice ephatch people.

P.S. Two more possible factors: I heel-toe downshift most of the time (just a blip, not a huge rev), and I use 87 octane gas.

[talonXracer]

Drive like a normal person, check your tire air pressures, do a ECU reset and idle relearn. Wide tires and excessive toe will reduce mileage.

[smykhaisouk]

even with all that it still shouldnt be that low. my v6 frontier truck gets about the same mileage. hope you figure it out. goodluckkkkk

[Rasy]

Pretty much what Talon said. Using anything higher than 87 is not necessary for higher performance or gas mileage, as our service manual states.

[totommo]

it's the way you drive. i do the same thing as you. everytime i drive aggressive and downshift all the time it drains my gas quick! but if you drive normally shifting at 3000rpms and using your brakes it saves way more gas. i drive normally now and it saves so much more gas could notice it without even writing down stats.

[jed_averill]

My last tank gave me 37mpg. 3k RPM shifts, slight press on the gas pedal and try to stay on gear as much as possible.

[MBaG]

My last tank gave me 37mpg. 3k RPM shifts, slight press on the gas pedal and try to stay on gear as much as possible.

3K rpm shifts? i think in the manual it shows when to shift to be most fuel efficient.

[jed_averill]

Yes I remember there's two. But the shifts were dependent to speed, not rpm. One was normal acceleration and the other was for cruising. Cruising is the one that gives you the most MPG.

[J Mo]

to the OP: your MPG is abysmally low, and i thought i was doing bad with my car, somethings not right : /

i do drive like you, except i dont heel toe, just rev matching downshifts; i did a little experiment and drove like granny for my last two gas tanks -- and i learned a couple quirks about my EP

these numbers are from 80% city 20% hwy, and i drive just 20 miles a day on average, fillup every 2 weeks with 87 octane

normal driving : 23-25mpg, low fuel light usually comes on at 9.5-10 gallons consumed (judged by the gas station pump auto click off)
granny driving : 25-26mpg, low fuel light came on at ~11 gallons consumed

now, i felt like with granny driving i had a false sense of security with the low fuel light coming on much later than my normal driving, i speculate that must be because im not punching it that much, the fuel aint pressurized that much or something along those lines

i was honestly disappointed with my granny mpg's, since i thought i was actually going to break in the high 20's given the "sacrifice" i did with the whole driving like [a hypermiler] thing, so im like, why bother? i'll just keep on driving normally and enjoy the car

ok, im done with my cerebral diarrhea episode :)

[amrcncllctble]

try this as long as you dont have a tune, disconnect both battery terminals for 15-20 seconds, this should give the pcm enough time to reset its adaptive strategies, reconnect the battery, start driving the car very conservatively, upshift between 2k and 2500, the vtec on the k20a3 is set up to maximize fuel mileage in that rpm range, also hondas cut fuel when the pcm sees less than 4% throttle in gear, so start slowing down earlier than usual and downshift without rev matching, if you dont see an increase in fuel mileage, i'd say you might need a new fuel filter

[Johnny]

Even if you race once a day for that whole tank, your mpg are still way off. Hmmm.


It's also good to learn when to leave it in gear when coming to a stop and when to put it in neutral when coming to a stop. You save more by leaving it in gear but sometimes have to slide it in neutral. It's a learning process. Always drive in a gear that gives you the lowest RPM's as long as your not bogging the car. Their's no recommended shift point on when to shift. It all depends on where your throttle position is. Learn to modulate the throttle. Don't heel toe as that's gas loss right their. You also save more by lightly pressing the gas from a stop and catching speed but watch out who's in back of you because you might get honked at.

I've stopped posting on Fuelly but it's a cool site. Last gas tank I averaged 36 mpg. I had to pat my self on the back. But then again, their's other times where I don't give a rats ass and get a measly 27 mpg.

I also have a scan gauge and have made my money back by saving gas and learning to modulate the pedal.

[talonXracer]

try this as long as you dont have a tune, disconnect both battery terminals for 15-20 seconds, this should give the pcm enough time to reset its adaptive strategies, reconnect the battery, start driving the car very conservatively, upshift between 2k and 2500, the vtec on the k20a3 is set up to maximize fuel mileage in that rpm range, also hondas cut fuel when the pcm sees less than 4% throttle in gear, so start slowing down earlier than usual and downshift without rev matching, if you dont see an increase in fuel mileage, i'd say you might need a new fuel filter

DO NOT disconnect the battery terminals!, Just remove the ECU/FI fuse from the underhood fusebox for 30 seconds and then perform a idle relearn, also the ECU shuts down the injectors at 0% throttle, not 4%

[Dorachagi]

After poking around the car I found the air filter was pretty dirty. It should have been cleaned (per my request) at the last oil change but I guess I should have gotten in the bumper and checked it myself. Did an ECU reset and idle relearn and the car feels noticeably better, so I'm thinking that was the bulk of the problem. Tires were slightly low too, but unfortunately when I went to air them up one of the valve stems is bad, it will only let air out, not in. So about to go this morning to get that replaced, after which I'll fill the tank and see how much difference there is in the MPG on a new tank. After I find out the new numbers I'll post back.

[Dorachagi]

OK, something has got to be wrong with my car. After cleaning the air filter, doing ecu reset and idle relearn, keeping tires at correct pressure, and driving like a semi-grandma most of the time, my mpg went DOWN (what!?!? DOWN!?!?) to 18.1 mpg. Oddly, the car feels noticeably better.

Spark plugs look fine, oil has been changed recently and also looks fine. Alignment is stock, wheels and curb weight are stock, the car is usually empty other than me and a backpack, and the only engine modification is a Fujita CAI. And the car only has 57,000 miles on it!

It did have a minor wreck a couple years ago, spun the car and rear passenger wheel hit the curb hard, bent the wheel and caused some suspension damage. But it all has been repaired for a long time, and no part of the powertrain was involved at all. And I have billet motor mounts, not sure why that would have anything to do with the gas mileage.

What else could be causing this? Should I just bite the bullet and take it to a shop? Please help ephatchers, really need some guidance here.

[RotaryGreg]

OK, something has got to be wrong with my car. After cleaning the air filter, doing ecu reset and idle relearn, keeping tires at correct pressure, and driving like a semi-grandma most of the time, my mpg went DOWN (what!?!? DOWN!?!?) to 18.1 mpg. Oddly, the car feels noticeably better.

Spark plugs look fine, oil has been changed recently and also looks fine. Alignment is stock, wheels and curb weight are stock, the car is usually empty other than me and a backpack, and the only engine modification is a Fujita CAI. And the car only has 57,000 miles on it!

It did have a minor wreck a couple years ago, spun the car and rear passenger wheel hit the curb hard, bent the wheel and caused some suspension damage. But it all has been repaired for a long time, and no part of the powertrain was involved at all. And I have billet motor mounts, not sure why that would have anything to do with the gas mileage.

What else could be causing this? Should I just bite the bullet and take it to a shop? Please help ephatchers, really need some guidance here.

this is peculiar for sure. although its hard to say how you drive. manual cars leave so much room for different driving....we are just trusting you on the grandma thing. i mean that could be bad too. bogging the crap out of it. in any case, if you are determined that its not your driving (which im not saying it is, im just saying you cant ever really rule that out when its a manual car) it could be something mechanical like a slipping clutch. also, if you had access to a good diagnostic computer you could watch the 02 and the fuel trims and see if any of that looks out of whack. like the o2 is getting lazy but the cross counts arent low enough to set a code....thats just an example. but its hard to diagnose anything these days without that sort of equipment.

[Dorachagi]

Thanks for the response. If it's the clutch slipping, should I be able to feel that while driving? And as far as sensors go, is that something I can check myself or should I take it in somewhere?

[talonXracer]

You say the plugs look fine, what type of plugs are they?

[Dorachagi]

Stock NGK plugs I believe. I bought the car at 27k miles and haven't changed them.

[Passenger]

Thanks for the response. If it's the clutch slipping, should I be able to feel that while driving? And as far as sensors go, is that something I can check myself or should I take it in somewhere?

Yes you'll feel it slipping if it is the clutch. Easiest way to explain how to tell is to take your car out on a short drive... Once you hit 2nd or 3rd gear, WOT, and if it responds strong then its not slipping.. if the engines revving w/o you accelerating then your clutch is burnt up to a certain degree.

[talonXracer]

How any miles now?

[RotaryGreg]

Yes you'll feel it slipping if it is the clutch. Easiest way to explain how to tell is to take your car out on a short drive... Once you hit 2nd or 3rd gear, WOT, and if it responds strong then its not slipping.. if the engines revving w/o you accelerating then your clutch is burnt up to a certain degree.

actually its better to use a high gear. sometimes with the gear advantage the clutch is less likely to slip, at least not noticeably. if you can find a hilly road and plunk it in 4th gear and go WOT at a moderate speed it will be very obvious if its slipping. however, this is very unlikely. if your clutch is slipping that bad you dont typically get away with it for long. I just said that as an examble of something in the driveline that could cause poor fuel economy.

as for the sensors, judging by your questions no, you cant do this yourself. even if you had access to the diagnostic equipment (lab scope or even a dealer system for diagnosing engine faults) you have to understand what you are looking at. these systems only show you what the sensors are telling the ECU, its up to you to realize whats good and bad.

[Deadphishy]

Lots of EP owners getting Poor economy. I wonder if the O2 sensors are pron to bad readings.

My O2 sensor went bad, and did not throw a code. But i had Kpro, so i could see that the sensor was only reading 10:1.

[talonXracer]

Good thought as O2 sensors do wear out and change what they are actually reading. It could be a contributor to these excessive fuel consumption issues.

[Deadphishy]

Good thought as O2 sensors do wear out and change what they are actually reading. It could be a contributor to these excessive fuel consumption issues.

This is a topic to look at, as more and more EP's are reaching middle age.

[RotaryGreg]

Lots of EP owners getting Poor economy. I wonder if the O2 sensors are pron to bad readings.

My O2 sensor went bad, and did not throw a code. But i had Kpro, so i could see that the sensor was only reading 10:1.

yes, this is directly in line with what i was saying. with a labscope, kpro, dealer diagnostic tools (we call it IDS at mazda) you can watch the o2 under varios conditions as well as fuel trims and all that jazz to see if anything looks out of whack. but without that equipment and the know how you wont get anywhere without just guessing and throwing expensive parts at it

[Passenger]

actually its better to use a high gear. sometimes with the gear advantage the clutch is less likely to slip, at least not noticeably. if you can find a hilly road and plunk it in 4th gear and go WOT at a moderate speed it will be very obvious if its slipping. however, this is very unlikely. if your clutch is slipping that bad you dont typically get away with it for long. I just said that as an examble of something in the driveline that could cause poor fuel economy.


Yeah but if the clutch is failing in anyway you'll still notice, no matter what gear. Mine was more noticable in 2,3&4 because thats the gears I used most for accelerating.
Have you checked your fuel injectors? Not sure if theres a way to do this but one of mine was like melted or something, I swapped all of em out and my mpg went up alot.

[Dorachagi]

Tried WOT to check the clutch last night and it doesn't seem to be slipping that I can tell. I'm not sure how to check the injectors, but I was thinking that if something was wrong in one of the injectors I'd see a difference on the spark plug from that cylinder, but all 4 had very even, similar wear and coloration. Going to take it in somewhere on Monday and have em check out the o2 sensor I think.

[BeaterEP]

Let us know what happens.
I've been having trouble with MPG slipping lately too. Oil needed changing, but even after I took care of that there's no change. I got the worst mileage I've ever gotten tonight; 24.4 mpg.
I've noticed more and more of the stations I fill up at have Ethanol postings on the pumps, any chance that might be killing my mileage?

Just grasping at straws here, really. I'm kind of out of ideas as to what might be causing the problem.

[jed_averill]

I compared shell gas and chevron gas and took it 100miles on the freeway (LA-SD). 87 Octane results.

chevron = 33.** MPG

shell = 37.** MPG


Could it be maybe each gas station differs from another? I thought it was weird.

[BeaterEP]

Yeah I don't know what the deal is. Everything has been running fine, except the oil needed changing. But even after taking care of that, mileage was down again.
Did an ECU reset yesterday, we'll see if maybe the old girl just needed a little kick in the boot to get back in line. :D

[jed_averill]

No leaks right? Good luck with everything.

[RedSiBaron]

i finally got to looking at this thread...

i have a couple questions; between your two fill ups, have you used the same gas station and did you do the same type of driving between the two tanks?

see when i was living north of philly a couple years ago, there were some BAD gas stations in the area, and they mixed a lot of ethanol into the gas at that time (or so i was told). in any case, there was a gas station i filled up at and got 18mpg just regular around town driving, some spirited driving, some grandma driving, some stop and go, etc etc...just regular driving. In ohio, driving this way i would get between 24 and 28 at the time. so how did i lose so much mpg? i wasnt sure, so i filled up at the same station again, and drove as economically as possible, still got 18mpg. tried other gas stations with varying results, but all low mpgs 18-22. then i did some asking around, and people said they had the best luck with a BP station near my apartment. (they didnt have shell stations around this town, or else i would have gone there)...well i went to this "good" gas station and after that my mpg went back up to 24-28...these days after i started running the mugen intake, ITR header, and mugen exhaust (not sure if it really matters what type i/h/e, but htere it is) i am now getting between 30-36mpg on shell gas.

thats my experience with bad mpg in the EP...

my main idea though, like others have said, is the o2 sensor. now that i mention it i do remember that when mine went bad i was noticing a slight loss/inconsistency in power, but also my fuel economy was down/inconsistent. I would also suggest checking your connection points on the o2 sensors to check for any corrosion. if the sensor is going south or if there is any change in resistance its going to throw the sensor performance off before it finally goes bad and throws a code

my other thoughts are bad compression, or too much fuel...are there any driveability issues?

[RedSiBaron]

i finally got to looking at this thread...

i have a couple questions; between your two fill ups, have you used the same gas station and did you do the same type of driving between the two tanks?

see when i was living north of philly a couple years ago, there were some BAD gas stations in the area, and they mixed a lot of ethanol into the gas at that time (or so i was told). in any case, there was a gas station i filled up at and got 18mpg just regular around town driving, some spirited driving, some grandma driving, some stop and go, etc etc...just regular driving. In ohio, driving this way i would get between 24 and 28 at the time. so how did i lose so much mpg? i wasnt sure, so i filled up at the same station again, and drove as economically as possible, still got 18mpg. tried other gas stations with varying results, but all low mpgs 18-22. then i did some asking around, and people said they had the best luck with a BP station near my apartment. (they didnt have shell stations around this town, or else i would have gone there)...well i went to this "good" gas station and after that my mpg went back up to 24-28...these days after i started running the mugen intake, ITR header, and mugen exhaust (not sure if it really matters what type i/h/e, but htere it is) i am now getting between 30-36mpg on shell gas.

thats my experience with bad mpg in the EP...

my main idea though, like others have said, is the o2 sensor. now that i mention it i do remember that when mine went bad i was noticing a slight loss/inconsistency in power, but also my fuel economy was down/inconsistent. I would also suggest checking your connection points on the o2 sensors to check for any corrosion. if the sensor is going south or if there is any change in resistance its going to throw the sensor performance off before it finally goes bad and throws a code

my other thoughts are bad compression, or too much fuel...are there any driveability issues?

[Dorachagi]

So now it's been two months of tracking my mpg. I've been checking the oil and tire pressures constantly and driving normally, and the highest it's gone was barely over 20 mpg. In the last couple of weeks I replaced the spark plugs and put a bottle of techron fuel cleaner in a tank of 93 octane, ran it all the way through, refilled with 93 and did an oil change with Mobil 1 5w-30 and used a mobil 1 filter (the old oil was dark but there were no sparkles or bits of metal at all), reset the idle again (even though it always idles steady, 1400 rpm at cold start 800-900 rpm warm). After running half the tank of gas and checking the mpg I got... 18.093 mpg. BARELY above 17!!! And the engine feels great now, really smooth. 02 sensor connections looked fine, I felt all over the exhaust and can't find any holes or cracks, alignment's fine, tires are always at 32 psi. I'm going to change the transmission fluid as well when I get to a friend's house with a breaker bar, the damn fill bolt defeated me, but it doesn't really feel bad either. No CELs ever. So, I'm kinda at loss, I guess I really am going to have to just take it in and get the o2 sensor checked. Beyond that I really have no idea what the hell is up. Any more ideas or thoughts hatchers?

[sleepy ep3]

You want milage? Buy a prius. Otherwise, grow a penis and STFU. Maybe if all of you kept your foot out of it, you'd get better milage. Secondly, cars use more fuel in the winter due to higher air density.

[Dorachagi]

You want milage? Buy a prius. Otherwise, grow a penis and STFU. Maybe if all of you kept your foot out of it, you'd get better milage. Secondly, cars use more fuel in the winter due to higher air density.

I'm more concerned that something is wrong with the car that I'm not noticing than the actual mileage, looking at it as a symptom.

[Passenger]

You want milage? Buy a prius. Otherwise, grow a penis and STFU. Maybe if all of you kept your foot out of it, you'd get better milage. Secondly, cars use more fuel in the winter due to higher air density.

He lives in Memphis, the air shouldnt be too much different than here in Atlanta.. he's getting worse milage than an evo. somethings wrong with his car.

[sleepy ep3]

He lives in Memphis, the air shouldnt be too much different than here in Atlanta.. he's getting worse milage than an evo. somethings wrong with his car.

Well, I don't know about Memphis, but it's 18 degrees in St Louis. I can't see Tenn being much warmer than that.

[Dorachagi]

It is pretty cold right now but it was almost 70 a week ago and this has been going on for two months in all kinds of weather.

[BeaterEP]

You want milage? Buy a prius. Otherwise, grow a penis and STFU. Maybe if all of you kept your foot out of it, you'd get better milage. Secondly, cars use more fuel in the winter due to higher air density.

Wow, helpful post there!
/sarcasm

How about you shut it unless you've got something useful to say?
A bone-stock EP should not be getting <20MPG, no matter what the weather is like. Guy's looking for help and suggestions, which is what the forum here is for.
Not smack-talking and bullshit.
The OP responded very civilly to your flaming, but I'd prefer you keep that shit to yourself and let the grown-ups get some work done.

[Dorachagi]

Wow, helpful post there!
/sarcasm

How about you shut it unless you've got something useful to say?
A bone-stock EP should not be getting <20MPG, no matter what the weather is like. Guy's looking for help and suggestions, which is what the forum here is for.
Not smack-talking and bullshit.
The OP responded very civilly to your flaming, but I'd prefer you keep that shit to yourself and let the grown-ups get some work done.

Thanks for saying everything I refrained from! :)

[Mighty_Mouse_Ep]

I noticed you said you had some suspension damage. Do you think the problem could be with an alingment. Are the tires on the car wearing evenly? Does the car veer to one side?

[Passenger]

Well, I don't know about Memphis, but it's 18 degrees in St Louis. I can't see Tenn being much warmer than that.

What I was insinuating was the temperature shouldn't be giving him 12 mpg less than what your average ep gets, and telling him to stfu isn't doing anything but make you look like an ass.

[BeaterEP]

I noticed you said you had some suspension damage. Do you think the problem could be with an alingment. Are the tires on the car wearing evenly? Does the car veer to one side?
Yeah, alignment could be a culprit (at least partially) if it's way out of whack...I'm guessing OP would notice if it was that bad, but worth checking.


What I was insinuating was the temperature shouldn't be giving him 12 mpg less than what your average ep gets, and telling him to stfu isn't doing anything but make you look like an ass.
realtalk

[Dorachagi]

The car did have some severe pulling to the right after the shop "fixed" it following the accident. After going to a friend and finding a bent tie-rod they missed and doing an alignment it went almost entirely away. There was also a ripped motor mount they hadn't noticed that was allowing enough movement to actually affect the handling noticeably, after replacing them with Avid mounts that problem went away. It does still pull slightly to the right some times but only slightly. I doubt the alignment is 100% perfect, but I know what it feels like when it's out of whack and it's fine right now. I worried something might not be spinning as freely on the wheel that got hit or even the brakes could be dragging somehow, but if there's any kind of rotational drag I think I'd feel it when lifting off the throttle, it would decelerate the car more drastically than normal, and I haven't been able to feel anything like that while driving.

[Dorachagi]

POSSIBLE SOLUTION!! Poking around the intake and throttle body today I found that the intake air bypass control thermal valve snapped off on the part of the t-valve where the little hose from the air intake goes on. Had a healthy vacuum leak, at least at cold start up, I believe it closes itself after coolant reaches 147 degrees Fahrenheit anyway. After researching the part it doesn't really seem necessary, so I've sealed it and taped it off, the hole where the cracked part was and the hose on the intake. I'll need to reset the ecu tomorrow and wait for the next fuel-up to check for an improvement, will post back then.

[sleepy ep3]

What I was insinuating was the temperature shouldn't be giving him 12 mpg less than what your average ep gets, and telling him to stfu isn't doing anything but make you look like an ass.

You can STFU too. :smootch:

[mitchell_ep3]

from summer temps, to winter... -25/30*C i end up getting 60 miles less to my tanks... but command start has its flaws :P

cold air = dense, more air/ more gas to meet that AFR

i wish you luck on the vacuum leak OP