Drumer56

Hello i've got a 2001 Honda Civic LX Automatic Sedan and i've been getting really poor gas mileage. I reset the odometer every time i fill up and for the past couple of months i've been getting about 20 mpg on average. Would changing the spark plugs or changing the fuel filter help with the mpg? Fuel injector cleaner?

Ive got about 200 pounds of audio equipment in the trunk but other then that and myself my car has no additional weight. Nothing aftermarket on my car other then a K&N air filter and a 2 Inch cat back exhaust which i would think would help with my mpg. Any help is appreciated i want to get my civic back up to doing 25+ mpg.

Thanks

EDIT: about 110,000 miles on the car

stoney13

Hey man I have your same problem. I drive an EX though but im sure what im trying to do is gonna be the same. I also have about 120,000 miles on the car. I also have an audio system and for a while my mileage was great but then it went from 400+ on a tank even when I was flooring it and now its getting about 250-300 miles to a tank.

I had a check engine light that wanted me to replace my downstream o2 sensor. Plus my catalytic converter was shot. So i replaced the new cat with a magnaflow direct replacement cat and a denso o2 sensor. Light was still on and mileage is still terrible. Talking with a friend he said the light will stay on until I replace the new o2 sensor with a honda one. It wont go off unless I do that and he said it was gonna be around $125, not looking forward to that. I even have an AEM V2 CAI plus Helix TBS. Plus I changed my brake pads cause they were bad and I changed my oil and oil filter. Still terrible mileage.

I talked to a friend who is a master mechanic specializing in diagnostics. He suggested to check the spark plugs and fuel filter (because if that is clogged then not enough fuel would be getting to the engine) after I explained what I had done to the vehicle. So I put it on the rack at a buddies shop and rotated and balanced the tires while my buddy was busy. I didnt have time to check the plugs or fuel filter because I noticed I was leaking brake fluid out the reservoir so I got side tracked.

Once I buy a new fuel filter and replace it, get the alignment correct, + check the plugs I will let you know if that solves anything. But it is annoying to keep filling up twice as often now. Its raping my account.

MindBomber

The intake and exhaust will cause slight drops in HP and fuel efficiency, all they will do is make your car louder. The extra weight and drain on the battery from the audio equipment will also have an impact on fuel efficiency.The fuel filter is not a wear item in 7th gen civics, it should last the life of the car without causing a drop in mileage. I get the best fuel efficiency from Shell V-Power gas, although some people prefer Chevron w/ Techron, any other gas station gives me significantly worse mileage. I would recommend you each go through Gearbox's forgotten tune-up mod DIY, if you do everything on the list you should have a fairly significant increase in fuel efficiency.
https://www.civicforums.com/forums/1...e-up-mods.html

TRIZ

iTrader: (14)

Disconnect the audio equipment for at least 2 fillups and see how much of a huge difference that makes. 200lbs is a lot of needless weight.

Get your tires back up to the correct pressure too.

And I second doing gearbox's forgotten tune up mods.

jim1123us

I have an 02 Civic EX AT with 72K on it and have a bunch of problems with it which started with a drastic drop in MPGs ( 30+ dropped to 16ish) so I thought I would post here first. I started out by doing a quick tune up, denso IK20 plugs and new air filter. Shortly after doing that the car threw a 0420 code ( CAT low efficiency). The car started to loose significant power - up hills it cannot maintain 30mph. I replaced the primary 02 sensor and did Gearbox's forgotten tune up. The CEL has not come back since, but the car drives no better. The engine revs just fine while parked but climbing hills it responds very slowly. Once the RPM climb the car doesn't shift until about 4K.
What I'm thinking is either clogged CAT, or transmission issue. Ideas? Any help would be great. The car is pretty much un-drivable now.

got2run5

Check to make sure you don't have a crack in your exhaust manifold. It is VERY common on this gen of civic. I have a crack in mine right now (gonna b replaced soon) and it dropped my mpg by 5 mpg. The crack makes the 02 sensor read wrong and dump more gas in. Pull off the exhaust manifold cover (a few tight bolts) and inspect for even hairline cracks.

sdaidoji

iTrader: (1)

sounds more like cat

jim1123us

gotrun5 - I'll take a look at the exhaust manifold. Would I hear the leak if it was cracked ( I didn't notice any hiss)? easy enough to check.

sdaidoji - Any easy way to check the CAT?

sdaidoji

iTrader: (1)

not that i know of... exhaust shop?

jim1123us

I tried to see what the temperature was across the Cat right after a test drive with my infared temperature sensor but the downstream side was beyond the range (>680 deg F). After a minute the downstream side was about 250 deg hotter than the up stream side. From what I've read here that is high. The cat was not glowing however. Maybe I'll try to drop it this weekend and see if is blocked.

jim1123us

Ok I pulled the exhaust manifold cover last night and saw no sign of cracks. I'll try to check the cat this weekend.

Anyone want to weigh in on the possibility that this is a transmission problem? Do the symptoms sound like classic 7th gen 2nd clutch issue?

got2run5

Sorry for taking so long to get back--you might not notice a crack. It can be pretty small and in hard to reach areas. But chances are you would hear a clicking (in my case) when accelerating hard (like at 4000 rpms and up) and I know some people hear a hissing sound.

jim1123us

hey guys - problem solved. It was the cat. sdaidoji gets the prize. I had it replaced today and the car runs like new. Shop said it was pretty plugged up. Thanks for your help.

Jim

sdaidoji

iTrader: (1)

pheeew!
Good to know it was solved!

Smarques916

I have experienced similar issues. I drive an automatic EX with 165,000 miles on her. I use it as a commuter so I don't have any stereo equipment or exhaust. I do have a K&N intake. I recently got a Verizon Hum X, which has a code reader function. The code reads P1457. I've changed the gas cap, o2 censor, catolyc converter but I am getting 20 miles per gallon. Attached are 2 screen shots from my Verizon Hum X app. I just tried to post an attachment. But it requires a URL