Fuel Economy Thread

[Lu Mcfly]

This is probably a stupid question but does the winter cold have an effect on gas consumption if you have a cold air intake?  Lately my car has been consuming more gas then it usually does and i just changed the oil so i don't think that has something to do with it.  Any help?

[Jeff Likes Bagels]

My assumption would be yes. Colder air = more dense air = more air getting into your engine = engine running lean = add fuel to mixture to make it less lean = more fuel consumption. Don't quote me on it though.

[Rich01]

I think that might be the reverse Jeff, i.e. a cold air intake is suppose to make for increase fuel efficiency so you should see a similar behavior. The grade oil you put in does affect your MPG, heavier=lower MPG and vise versa. I could be wrong, but my understanding is colder air leads to a more complete combustion, hence increase MPG.

[Mike]

Colder air yes but, in some areas we experience extremes. The other thing to think about in line with your thought is that colder weather will make your oil thicker. The other obvious question is have you been warming up your car before driving

[InFuMoUs]

Don't they also add something into the gas depending on the season...like summer blend and winter blend? Maybe that can also affect fuel effeciency.

[CrackerTeg]

Ethanol is your enemy. Winter blends tend to have more of that shit which leads to a little worse mileage.

[v6sicksspeed]

how big of a swing are you seeing in mileage per tank?  typically on a highway-heavy run i can pull roughly 400 miles out of a tank and over xmas i did just that.  right around 420 miles from a topped off tank to one with about a gallon left in it.  that's about 95% highway too... 28-30 MPG approx.

[Lu Mcfly]

Well your right about the cold air making the oil thicker which can be a cause, but as far as for Ethanol i didn't know about that. The MPG I've been seeing about 300 miles per tank not precise though where before i would probably see some where around 350-400 maybe and its mostly city highway's but some city streets as well.

[stirfriedferret]

So my issue is that my car has been giving me poor fuel economy...  I'm not sure if it came slowly or instantly, but I noticed a big change in fuel economy recently.  I'm not sure if it could be modification related or not, but I'm not exactly sure what the issue is here.  Maybe some of you members can help me troubleshoot and give me tips on what to look for.  I own a 2007 Honda Accord coupe.  It's a 4 cylinder, so I should be getting decent gas mileage.  It's rated at 24city/34highway.  I drive roughly 110 miles daily all highway, so I should be getting ~450 miles out of the tank, give or take a few miles for a little city driving, but instead I get around 350-400 miles to the tank.  I don't drive aggressively so I know that it's not me.

Here's a few things that I've checked already:
STFT (short term fuel trim)
LTFT (long term fuel trim) - Around 3% so it's actually adding a little bit of fuel. It's negotiable. I have the icebox mod, tb coolant bypass, tb heatshield, etc etc.
IAT - normal
Load - 20% at idle.  I'm not sure what's normal for our car, but I figured that was since I'm DBW.
CTS - normal
Intake timing adv. - normal
Tire pressures - ~35psi cold (all around)

So I figured that the engine is running fine.  I have no MIL set.  What else could the problem be?
I don't have my fender liners (as they ripped off)...  Not sure if that contributes to anything
I have poor alignment also since I just recently lowered the car more.  I know that can affect fuel economy, but I figured that it was slight.

Any ideas?  I can put up with it for now, but I just want to figure out what the issue is.

[Mike]

A bad alignment would cause more than a slight loss. The car has to work harder to achieve the same speed/ distance. I would get that taken car of right away.

[NWINNIE34]

check air filter....spark plugs....maybe try running a can of seafoam.... could be an injector issue possibly....
also could be a shitty gunked up catalytic converter.....you experiencing any funky smells ?  fart/sulfer like stank ?

[stirfriedferret]

Oh right, I forgot to mention.  Air filter is new.  I checked the spark plugs a few weeks ago and they were good (no fouling, etc etc).  Not so sure about the faulty injector...  Catalytic converter should be ok.  No funky smells and the afr is switching back and forth around 3% so it seems okay...  Any other ideas?

[neoryan7]

Your O2 sensor? What weight oil are you using? Your driving style? I go to cal poly and if I drive normally up Kellog hill I only get 18mpg. If I keep it slower i get 24mpg.

[stirfriedferret]

I haven't checked my o2 sensors, but I believe that they're a non serviceable item and they only get replaced once you get a MIL light.  I'm using 5w-20 synthetic pennzoil platinum right now.  I know my fuel economy issue isn't related to that because I noticed it before my oil change.  I drive very calmly without any hard acceleration.  I rev to 3.5k the most on a daily basis.  My route to school is 5n -> 55n -> 91e -> 15n so I don't go up and down any hills at all.  My fuel economy should be pretty damn good. I'm just confused.  I'll get an alignment this weekend and see if anything changes.

[Mike]

You can do resistance test on your O2 sensors to check for proper operation.