WKD DRGN

I have a 2000 Honda Civic Ex with 250,127 miles on it.

Recently I started getting some bad gas mileage. I decided to send out the fuel injectors to get ultrasonic cleaned. In the meantime of waiting for those to come back, I changed out my fuel filter, fuel pump strainer, replaced the air filter (with K&N), and changed out both 02 sensors with NTK ones.

Now the weather has changed to around 32 and below (down to 19 degrees at times for a day...) and my gas mileage is even worse since putting the cleaned injectors back in. I have no idea what could be causing this. I have read that extreme cold weather can cause gas mileage to go south but my co workers who have newer cars say their gas mileage is the same. Don't know if that's cause we're talking about a 2010 and 2008 vehicles. No engine check lights at all. I had overfilled my oil a bit and decided to change the oil a little early and correct that problem today. Haven't driven it yet since I did that. We have gotten snow and ice and one or two days was driving around 20-30 mph everywhere I went. Figured that didn't help.

Also put brand new tires on my car all around. I got GT Radials Champiro's. That's the only thing I went kinda cheap on the car. Everything else was top quality parts. The tires seem to be doing great in the snow and ice at least.

Any help or suggestions??

Looks like I am getting 18 mpg when I used to get 28-30 mpg.

ezone

Cold weather eats up a lot of fuel.

My 12 is down to around 21 MPG since it got bitter cold here. Doesn't help that I remote start it when it's in the single digit temps so it can warm up, and my daily is 5.6 miles each way. My engine almost never gets to full operating temp this time of year, and that eats fuel.

Bad:
Heavy oil
cheap tires
Low tire pressures
Winter fuel blends
Ethanol
Warmup times without moving
Brake drag
Bad habits
snow
traffic
stop lights
drive-thru
sitting in the running car during lunch hour

How much driving is done, and what % is your driving while the engine is cold vs fully warmed up?


Scan for
Fuel trims
ECT and IAT values
MAP
and valve adjustment

Double check
Cam timing? Ignition timing?



Everyone complains about mileage this time of year, there's not much anyone can do about it and most of the loudest complainers at work can't (or refuse to) comprehend why mileage drops.
Sorry, no good answers other than wait for warm weather?

WKD DRGN

Thanks for the detailed post. I don't let my car idle at all in the mornings before work. Just start it up and go. I drive 9 miles to work and the engine gets to operating temp about 5-10 mins into the drive. I believe the valves need to be adjusted there is a slight tapping at start up. Haven't gotten that done yet.

Just got a detail oriented scan tool. Will have to read the manual on how to check the things you mentioned. I will try to do that sometime this weekend.

Not used to the temperatures we are seeing the last couple of weeks. We are breaking records here in VA with these temps. So I couldn't really recall how my gas mileage has been affected in the past. But I do understand how the cold weather can affect it. Hopefully warm weather is coming soon!

WKD DRGN

Hooked up my scan tool today on the way to work.

ECT stayed around 170 and didn't go higher then 188.

I can't remember if the MAP or IAT said 30 degrees. Sorry still learning.

I watched the fuel trims and they for the most part jumped around negative and positive values not exceeding 9.0.

I did however notice the o2 sensor from Bank 1 was going crazy voltage wise. Like jumping around all over the place and big leaps too. I read that's normal for bank 1? Bank 2 stayed steady for the most part at around .780 volts. It would go up to .9xx and sometimes would zero out but for the most part stayed steady.

That's all I can remember for now. I don't know if I can check valve adjustment through the scan tool?

The temperature is in the 20's and 30's today.

ezone

B1S1 sensor is supposed to swing far and swing fast. Anywhere between 0v to 1v is ok.
Short term fuel trim reflects those swings, STFT is always moving.

Rear sensor B1S2 is supposed to be more stable after the cat is hot and operational. Very slow swings when compared to the front sensor. It is mostly used for checking the cat operation/efficiency, but it can and does influence some of the fuel injection amounts at times.


Zero fuel trims would be the base fuel calculations as determined by the programmed fuel injection map (table) inside the computer.
The front O2 sensor is the main feedback sensor to tell the computer if the fuel mixture is lean or rich, and the computer tweaks the injection amounts accordingly and assigns a number, or % above or below that base fuel map. This is STFT number.

Long term fuel trim gives more of an indication of fuel adaptives, based on what the STFT is doing. If STFT stays high for a long time, LTFT is moved a step higher to compensate. This goes on until the STFT is brought back to near zero, if possible. (You can watch this happen on some engines by creating a vacuum leak, but this doesn't work on most older Hondas.)
LTFT is very slow to move. Might be described kinda like a multiplier factor.

That's not far out enough to set any code, it's probably ok.
IAT is Intake Air Temp, in degrees. MAP can't be given in degrees, it's the manifold vacuum reading.
170 operating temp while running down the road at highway speed? Might be ok, might not. Seems a smidge on the low side, but I do see the cars run operating temp that low at times.

I've been thinking about sticking a 195* stat in mine to see if I can get a little better mileage out of it. Not sure if I'll ever do it though.

WKD DRGN

Sorry I read your reply while on break at work and didn't get to reply back. I got sick Sunday night at work and have been sleeping most of this time. Your post was very informative though.

The 170-188 temp was most likely at speeds of 45-50 mph.

The car is at another shop right now for unrelated issues. It's not having any other issues just getting some stuff done. Doesn't matter anyway cause we're about to get hit with 5-7 more inches of snow by Thursday.

Will update after weather gets better and I get more consistent fuel mileage.

WKD DRGN

Hooked up the code scanner today and got these readings.

22 degrees outside temp.

ECT 177

LTFT 2.3%-3.9% (varying through different speeds)

MAP 7-13 psi

IAT 44

There was some low end readings of the MAP when I got on the bypass and hit 60 mph. I don't know if this means anything. But it got around 6-7 psi for a little bit. Any further help would be greatly appreciated.

Also gonna go to get my exhaust checked out today to make sure there are no leaks. I've had leaks in the past.

ezone

MAP varies directly with engine load. If you hammer the throttle wide open, manifold vacuum drops to near atmospheric pressure.

Is MAP reporting accurately? Fuel trim seem to indicate "probably".

Hensinger2010

I know last year the solenoid purge valve on my 7th gen took a crap and dropped my mileage almost in half, I did get a cel and a code that pointed to it though, it would sometimes not come on intermittently, sometimes on right away, but was a pain for me to change because its mounted by the canister next to the gas tanks on seventh gens, screws were rusted and brittle, (Ohio weather :/ ), on the 6th gens everything is under the hood instead, way easier, but may be something to look into, maybe not just trying to help, I've heard horror stories of the purge valve going out on older Hondas and frying the ecu because of a short, not an attempt to scare you just to think outside the scan tool.