98 civic dx. Mods/upgrades: Megan header, custom axle back exhaust Megan carbon muffler 2.5", cuz dx header deleted cat, stock midpipe, msd stock replacement cap, rotors, and wires, iridium plugs, aem v2 CAI, form and function coilovers, changed wheels from 17" to 15", I know that stock is best but what of these need to be ditched back to stock and what can stay and why it hurts or helps for better gas mileage.

 

What is your current average gas mileage? Have you checked the ignition timing?

 

None of that stuff hurts fuel economy much because most of those parts don't really do anything but look/sound nice.

Changing driving habits will have a great impact on fuel economy.
And like you said, stock wheels will help.

 

Driving habits will have the biggest impact on fuel economy, shifing into a higher gear at lower rpms, cruising as long as possible down shifting. Just drive slower all together!

 

Bigger heavier wheels have more unsprung weight. It takes more horsepower to get them moving and increases stopping distances. Gas mileage differences are negligible but you do benefit from smaller/lighter wheels. Ask me how I know.

 

drive slow homie.

 

yeah lighter wheels help but u also gotta look at that if with the bigger wheels you get a larger tire diameter then itll drop ur rpms at hwy speeds.

 

Well first off I only get about 25-29 mpg. I'm not too familiar with ignition timing but it may be time for me to replace my timing belt. I bought the car used and I have all the documented repairs and has 190k on it with one belt change

 

your close to 30 mpg....

and your complaining?

drive 55mph...youll notice a little difference..however, a brand new civic at its best was getting like 34-36mpg highway....after 200k, id say your doing damn good.

 

Your MPG is pretty close to what I am getting with my auto DX. Driving habit's can really improve or hurt gas millage. I know this for sure.

I am all stock, and run 15's as well. I average 22 around town, 25-28 if I am nice to it. Also, that is a little bit of highway mixed in.

You should be getting ready to throw a timing belt and water pump in the car. I would change it within 5-10k. I just did mine as well, not too difficult, but can be a pain in the but.

 

I have 225000 miles on 97 Hatch and get around 34 mpg on combined mileage. If I drive from LA to the Bay area, around 400 miles, I get around 40 mpg.

Your driving habit is the number factor concerning mpg.

 

my civic has 200k+ and im averaging 35-37mpg on the high way and 30mpg in the city.

its all in how you drive, and your tire pressure has a big factor in it as well. make sure they are at 35psi

 

a change in the route you take may help , avoid lights and stopsigns congested roads. also check tire pressure and oil level each time you fill the tank

 

How old is the new head? Valves settle after break-in (although I'll admit I'm not familiar with your particular setup). Have you opened it up to check the lash since installing it?

 

Clean/repair ALL electrical grounds, get an ohm meter and measure the ohms value of each ground to the negative battery terminal. If the ohms value is higher than about 0-1ohms, you need to clean all the associated grounds, though you should start with the battery ground cable first to make sure you don't affect the other readings. Be sure to read the ohms value with a probe from the body of the o2 sensor to the battery ground. If the ohms value is higher than about 2ohms, the o2 sensor's output becomes so garbled to the ECU that it will tend to ignore it and run rich yet not throw a check engine code. One way to tell is to see if your car is running a faster idle after warmed up (750rpm instead of 670rpm for Y7 engines)


REPLACE PCV VALVE, that alone will improve fuel economy by 10% if it's clogged. Clean IACV and throttle body, adjust valve lash, just give the car a really good tuneup. Drive with fuel economy in mind and you should be able to average 40-45mpg easily in that car....assuming you care about fuel economy. If you have done all of the stuff I mentioned above and you still don't think the car is running quite right, then I suggest trying a seafoam treatment but I would do that LAST not first.

 

drive slower on freeway.. driving 65 on the freeway rather than 80 really improves your mpg alot..... if your on streets... dont do quick starts and hard stops... let your engine slow the car down...(coasting in gear) uses no fuel .....the way i think of it is try to (NOT) use your brakes at all....

and if all fails and your still getting under epa... then maybe its time for a tune up


and if i was driving your car.. id change the headers/exhaust/intake back to stock

 

I average 33 mpg with my 97 DX with A/C on and oxygen sensor cel on

 

An alignment is key if its not already done and tire pressure for a combo of less rolling resistance. I miss driving VX's shift light FTW!!!

 

***Run a CAT*** I wouldn't complain with what you average and with 190k. It's a 4 banger!