Fixmyepa

Help, I can't seem to figure out why my civic is getting terrible gas mileage. I have a 1998 ho daughter civic lx 4 door automatic. I'm only averaging 17-18 mpg's.
I've replaced the fuel filter, spark plugs, wires, cap, rotor, coil, replaced old intake with a cold air intake, welded up a hole in the exhaust manifold and replaced the o2 sensors. My air fuel gauge reads stoich right where it should and I've ran seafoam and k100 through the car a couple of times to make sure everything is clean. I've changed the oil and filter with synthetic just to be on the safe side and still no improvement to fuel economy. Also I drive very easy, i don't ever hammer the throttle down.

TL;DR - replaced a bunch of stuff and car still only gets 17-18 mpg. Help.

thanks guys!

Colin42

Brakes dragging? Low tire pressure? Bigger than stock rims? Crap gas? Crap tires? Vacuum leaks?

Fixmyepa

brakes aren't dragging, tires are newish and I keep an eye on the psi (32) stock steelie rims, and I've gotten gas at several different gas stations just to test to see if it was just a particular gas station and they all give me the same mpg. And no vacuum leaks, did the brake cleaner spray test.

ezone

Has the car ever given better fuel economy?
Driving habits and situations vary as widely as people.
Heavy traffic is a killer.
Any time the engine is running and you're not moving 45+MPH, your average fuel economy is dropping.


Got fault codes? Scan data? Fuel trims?
Cam timing?

Fill tank. Write down mileage.
Take it out for a highway run at steady 55 MPH for a few hours, then refill tank and write mileage. Calculate real fuel economy.

Fixmyepa

I drive very sensibly, never really put my foot down it's just a point a to b car but I do live in Houston where some of the most terrible traffic is. But I've logged highway and non highway miles, the tank that was mostly highway I got like 18 7 mpg and non highway i got around 16.4 which seems terrible for a 1.6 4 cyl.
as for codes I had a o2 sensor code found a cracked manifold so I welded the crack and replaced both o2 sensors. Code went away.
and it does have higher mileage around 240k but it had its timing done at 220k from a honda dealer.

ezone

Driving sensibly doesn't matter if all you do is sit in traffic with the engine running, burning fuel, and not going anywhere. All that time stopped you get zero MPG, that's included in and brings down the average per tank.


If I got that low number, knowing how I drive and my daily commute......that would be an absolutely horrible figure for me.
That doesn't automatically mean it's timed correctly.