Random poor mileage.

[TS2008]

Hi guys

My car: 2000 civic, automatic, dx.

I try to pinpoint the cause of the random poor mileage of my Civic for a while but I found nothing so far. In average, I get 30mpg in the HWY. The worst I got was yesterday, 25mpg. But today, I traveled in the same HWY, the same speed with the same distance and I got 35mpg. WTF ??

I bought a obdII scanner in order find out what cause the random poor mileage. I have zero error code so far and my O2 sensor looks good shape. The fuel trim LTFT and STFT are also both look fine.

I use Torque Pro for monitoring my mpg and It shows always 35mpg while I'm driving in a HWY. But my real mpgs are always much worse, except today my mpg match with the Torque Pro.

I first suspect there is fuel leak somewhere, but I found nothing and my car doesn't smell gasoline.

So I need your input about what thing I should look at or what things I miss.

anyways thanks.

 

[Joe Mason]

I wouldn't rely to heavily on that reading. Do it the old fashioned way. Divide gallons into miles when you fill up. Use your trip meter. But, either way, check your tire pressures. That could be contributing.

 

[Mr.Baker]

Out of curiosity, when was the last time a basic tune up was done?
How many miles on the car?

 

[TS2008]

The mileage is 87K. I bought my car last year. The wires look new and I changed the spark plug for the platinum. I had zero misfire and I also changed the air filter few months ago.

What bugging me is the huge difference of the Random poor gas mileage (25 to 35 mpg). But what It's funny is I don't see anything abnormal with the LTFT and STFT. They are all within +/- 2%

 

[TS2008]

Update:

Finally it was a little leak from top of the fuel filter between the banjo bolt and the washer. I didn't waste too much time with the leak and I changed the fuel filter and the washers. There have been a week now and I have a steady 44 +/-1 mpg while driving in a highway. Anyway knock knock.