Gas mileage gone bad.
 

I have had the car for almost 2 years now. Daily Driver.

I drive it the same way everyday. Half spirited(shift at 4000-5000 rpm range), half slow. Mixed city and highway-mostly city driving.

In the past week, I noticed my gas mileage had dropped dramatically during my daily commute to/from work. The gas gauge needle goes down so much after such a small distance. I did not change anything or add any weight to the car. No gas leaks from what I can tell. Engine idle is good, no CEL light, drives and runs smoothly. Oil level is good. Air filter is new. Tire pressure is correct.

Basically after 18 miles of driving, I had used up 2 gallons of gas. I have been averaging 9mpg this past week when I usually get 18mpg average on my daily commutes.

Are there any other reasons for the decreased gas mileage? It has been very hot this past week. 90+Fahreheit. Not sure if heat could affect gas mileage that much.

How do you know you used two gallons? Just by the fuel gauge? The fuel gauge is a best guess. Although, if you noticed the needle moved that much (about 2X) when it usually doesn't, could be something there.

Keep driving it until 1/2 to 1/4 tank, then refill and calculate the fuel consumption by hand?

Correct! thats what I do its more accurate if the gas gauge needle is below the center.

@ ProjectM96... Hot climate can affect miles per gallon also try cleaning the fuel system.. ;)

put your durametric on it. you might have a bad maf read code that hasn't shown up as a cel yet. it the ecu doesn't trust the maf it throws more gas at things to stay safe.

i cleared a similar fault code (wasn't showing as a cel) and my mileage went from 400 kms to 550 kms per tank.

Quick question for you all related to this.

Recently, I've been having the same issue, along with decreased performance on my '02 S. No CEL. Plan to have the codes read, but wanted to try disconnecting the MAF for a short period first to see if that's the issue. The dealer is almost an hour from my house, so I want to save the trip if I can.

The question I have is will that do me anything if I don't clear the code before driving it, or will the code still be present causing the condition I'm testing for to still exist?

+1
The only way to be sure is to divide miles driven by actual gallons used. Our gauges are flaky (to be polite).

Everytime I fill up the tank, I reset the mileage counter so I know how many miles I drive on a tank of gas.

It looked like the needle on the gas gauge was going down much faster than usual. So I went back to the gas station the next day and refilled it to see how much gas I really used in that 18 miles. It filled up with 2 gallons of fuel.

the gauge is not a reliable means of knowing your consumption...

http://986forum.com/forums/uploads01...1340629208.jpg

i did not get 400 miles from a tank of gas on this trip.

what i have learned from my gauge:
- needle hits 3/4 tank after about 50 miles.
- needle hits 2/4 ( ;) ) tank after about 200 miles.
- needle hits 1/4 tank after about 260 miles.
- gas warning light comes on around 310 miles.

You will not get an accurate measurement after only 18 miles. Like I said before, drive until you're at less than 1/2 tank. Better, less than 1/4 tank. Then refill and calculate. Fill up from the exact same pump you used on the last fill-up.

Tony, congrats on your 1,000th post!

Yesterday, as I hit 200 miles on the current tank, my van's fuel gauge was reading just over 3/4 tank. By that estimate, I should be getting over 800 miles per 20 tallon tank. Roughly, 40 MPG. However, grossly inaccurate. Sure enough, after just over 500 miles, I was empty. Came out to about 26 MPG, which is normal.

Here are my gas mileage results for my 2.7L. Very interesting difference between city and highway and type of driving.

90% city driving, 10% highway. Daily to/from work. Spirited driving. Shift at 3000-4000. Sometimes at 5000rpm when accelerating quicker. Stuck in traffic half the time. A/C On most of the time. 20 lbs of tools in the trunk.

1/4 tank = 49 miles
1/2 tank = 122 miles
3/4 tank = 190 miles
7/8 tank(Gas Light) = 222 miles

90% highway, 10% city. I took a 3 hour trip to visit gf when testing this.
Mostly between 3000-3300 rpm, 5th gear. 30 miles cruise control @3100rpm. A/C On. 50 lbs of luggage in trunk. Average outside temperature of 98F.

1/4 tank = 103 miles
1/2 tank = 220 miles

Refilled gas tank when I reached half tank/220 miles. According to the gas gauge and the pump, the first half of the tank is exactly 9 gallons of gas.

On the way back from my 3 hour trip.
Driving faster mostly between 3200-4100 rpm, 5th gear. Never used cruise control. A/C On. 60 lbs of luggage in trunk. Average outside temperature of 94F.

1/4 tank = 120 miles
1/2 tank = 222 miles