Need help. Getting bad mileage on my civic

[Rikaro]

Hi guys, see if you can help me out. I recently brought a 93 civic hatchback 5spd dx. Getting really bad mileage lately. I don't know if it's partly because of my driving, or the fact that i'm doing quite a few mods on the car. I'll list the stuff out and hopefully i can get some help.

I used to get 250 miles in a 8.4 gallon fill up. Lately i'm only getting 150-180 miles only. I'm filling it with just regular.

Here's the stuff i did to my car.
-from 175/70/13 steelies and all season crappy tires to 205/50/15 summer tires (falken azenis) and the 15" rims are 11 lbs.
-32psi on all four tires (is it safe to have nitrogen and oxgyen mixed in the tires?)
-lightweight lug nuts
-took the mud guards off (might hurt the aero especially on the rear)
-brand new o2 sensor
-new igniter
-gutted the rear out (no rear seat, spare tire etc)
-front and rear strut
-took stereo out.
-changed air filter, but back to oem now.
-engine oil, and oil filter changed.
-spark plugs

summer's here, would the heat lower my mpg? (i live in vancouver, bc, so it shouldn't be too hot)

may be i should change the sparkplug wires, or even do seafoam. Any other suggestions i can do to raise my MPG? People who owns the same car as me locally are getting at lease 300 miles in a tank.

help me out guys. I'm kinda pissed off to get this MPG on a CIVIC!! :(

[Erdrick]

That does sound kind of odd. The bigger tires will definitely make A difference, but not that much.

Are you sure you didn't mess up anything when you changed the O2 sensor? During the air filter replacement, could you have possibly messed with the mass air flow sensor?

What kind of reading do you have on the odometer? Have you changed your driving style recently?

As for the nitrogen, oxygen... well, I high doubt that you would ever have put in straight oxygen. What you mean is air... which turns out to be around 80% nitrogen (or something like that). Pure nitrogen has no carbon dioxide or oxygen, which is what places have been pushing as its strong point. So, to answer your question, you are fine to mix AIR and nitrogen.

[Erdrick]

Oh, and welcome to the site. You should start a garage entry for your car and track your mileage on the site!!

[96hb]

I'm not sure what the problem could be. You should definitely be getting more mileage than that! :eek: Does it still have the stock SOHC d15 in it? I drive a 96 hatch with gutted rear, same size tires as you and light rims, and dropped on Ground Controls, and I'm getting around 47mpg and over 400 miles to a tank. Only thing I can think of is your driving style. Are you taking off fast and redlining all the time? Even if you were you should be getting better mileage! I try to drive smooth, shift between 2-3k, and cruise 60-65 on the interstates. I know your tires have a pretty sticky compound, but that shouldn't affect your mpg that much. IDK. :confused: Oh yeah, I did raise my tire pressures to 40psi from 32. Still within the max sidewall of 51psi. Try adding a few pounds to the tires. It will reduce the rolling resistance. Lets see some pics of your car.

[88HF]

when exactly did you notice the gas mileage problem?

[SVOboy]

Wow! Something is very wrong with your engine...I would try doing a compression test and checking the ECU just to make sure it's not throwing phantom codes...welcome to the site.

[brucepick]

I also think something might be seriously wrong if you're getting approx. 1/2 the mpg you would expect. But have a look over these points...

Any aerodynamc problems? Like bumper cover or air dam cracked and hanging loose, or anything like that? Roof rack or aftermarket spoiler added?

You put in a new air filter when you went back to the oem type filter, right? My son's air filter didn't look toooo bad, just a dull gray instead of white. MPG went up maybe 15-20% with a new filter, that old thing had about 50K miles on it and didn't really look bad!

Spark plugs - did you get basic standard plugs as in owners manual, or maybe got some whiz-bang type designed 10-15 years after your car? I know that for our old Volvos we need basic copper plugs, the message boards are full of stories re. platinum and onobtanium etc. plugs just not working out.

Engine oil - use the lightest weight recommended by the Honda specs for your car for your local temperatures. My owners manual recommends 15-40 or 10-30 in my climate, so I'm using 10-30. Old-school wisdom recommended really thick oils like 20-50 which was fine in the good old days of moster V8's etc.

Tires:
Pump them up to "max sidewall", whatever is imprinted on the tire itself. Vehicle tire specs are for your comfort, not for mpg or handling. If your tires are rated 44 psi or higher though, maybe just go to 40 and see how you like the ride, then maybe go up from there. 32 psi is really low for anyone going for max mpg.

Pump and measure tires when cold in the a.m. The spec'd pressure limit takes into consideration the fact that they will warm up with afternoon temperatures and with driving. I have to drive a couple miles to the pump so I bring them up to maybe 2 lb. over my target, then check again the next morning before starting up.

[TomO]

Check to make sure that you don't have a dragging brake as well. Otherwise most other suggestions have been covered.

[jwxr7]

How do you drive? Did you change driving styles? Are you adjusting for the tires being about 1.9% bigger? Even if you drove the worst way possible a civic should do better than that:confused: .

[96hb]

How do you drive? Did you change driving styles? Are you adjusting for the tires being about 1.9% bigger? Even if you drove the worst way possible a civic should do better than that:confused: .

It has to do alot with driving style. I have the same rim/tire size combo on my Civic and my last tank I got 47mpg. Even when I used to dog the sh*t out of it my mpg was still in the 30's. Gotta be a combo of driving style and some mechanical failure somewhere.

[Rikaro]

i changed the o2 sensor because of bad mileage but it didn't help. It's probably something else

[VetteOwner]

change your wires! thier prolly more important than the plugs themselfvs

[Rikaro]

ok. so i think i'll go for the spark plug wires. A quick question though, do i need 8mm or 10mm ones for better mileage? also would one or two disconnected spark plug wires lead me to get bad mileage? or it won't even start up at all?

thanks

[Gary Palmer]

If you replace the wires, get the 10mm, they will allow more current to flow. If you have one or more wires either loose or disconnected, it will significantly affect your mileage. How it runs and how much it affects you would depend on which wire or wires are loose, disconnected, crossed and so forth.

It will start and run, under some conditions. I have had two wires be crossed and the car idled ok, not great, but ok, but when I tried to drive it, it had really lousy power and took forever to get up to highway speed. It did run though, which surprised me.

[Raccoonjoe]

I've had several cars run with crossed plug wires before. (It makes a great practical joke....)

Also remember to take into account for your tire size. Your new tires are 1.9% bigger than the old ones, so your MPG formula would look like this (odometer*1.019)/gal. Basically, just take your odometer reading for a tank of gas, multiply it by 101.9% to get the actual reading......then divide by gallons used. PM me if you want/need this in automagical spreadsheet form....

[Weliin]

I was getting bad gas millage from my 98 civic (about 23mpg in the city) and I tossed in a bottle of gum out fuel injector cleaner and all was good again.

I now toss in a bottle every 3.5-5k miles. It seemed to help me.

[VetteOwner]

yea i ment plug wires. thier realtively cheap. i usualyl run seafoam every oil change. it does wonders...