craig72

Hey gang, I have a 2007 with about 110k miles on it. Over the past few months, I have noticed that the fuel economy is not what it used to be. My driving is about 70/30 highway/city and I would average about 27mpg according to the display. Nowadays, using the same gas, same driving, and same display, I have been regularly seeing about 23 to 24mpg for the tank average. Last year I replaced plugs (OEM) and air filter.

The only oddity I can think of was over the summer, I had inadvertently filled the tank up ALL THE WAY. I think this might have caused an issue with the EVAP system, as when I would get on the gas, the car would cut out almost like it was shutting off fuel, only to come back almost immediately. Ran like crap if you hit more than half throttle for several days. It never threw a code, but it was very repeatable until the gas level went down to about half tank. I have have not had any issues since then.

So my question is, could the drop be related to that? The only other thing I can think of is O2 sensors. I know these go bad over time, and they are all original, so perhaps they are just causing the car to run a bit rich, but not enough to throw code? I have a good OBD2 scanner that will show me the sensor parameters while the car is running. Is there anything I can check to see if they are out of whack?

Thanks for any inputs!
Craig

hypervish

The drop is likely due to winter blend fuel.

Also, check your tire pressure. Tires drop 1 psi for every 10F drop in temperature combine that with the natural loss of air in tires and you can have a large impact on fuel economy.

nevernu

the only thing the svc manual says is about checking resistance to see if they are good. ofc u have to get access to them

maybe u can access it at the ECM

edit edit also do u rely on the fuel consumption gauge only cause those values can get skewed over time; a reset of the fuel economy system to recalibrate is useful. go to display fuel eco and hold down the button for several seconds

craig72

Hey guys. Thanks for the feedback.
This trend started happening a few months ago while it was still plenty warm. Also, I have had this car for several years and never seen this happen.

The tires are filled with nitrogen, so they don't suffer the pressure drop. However, as an exercise with my son for Boy Scouts, we had just checked them about two weeks ago and they were sitting right at 30psi.

As a matter of fact, I am simply looking at the Tank Avg on the display. I did not realize those could get out of wack over time. I'll try resetting like you suggested and see if the situation improves.
I'll report back what I find out.
Thanks again!

craig72

nevernu - Quick question.. when resetting, does the display need to be on 'Avg' or 'Tank Avg'? Also, which button am I supposed to hold down? The 'Disp' button? Thanks again

nevernu

its the avg fuel consumption display and hold the disp button down for more than 2 sec: p110 manual.
once reset it will read high for a while and drop as it gets more info...

craig72

Thanks. I gave that a shot last night before the drive home. It actually started really low then gradually worked up to about 25.4. I think on the next fillup, I'll reset it again, and the Tank Avg will reset as well. Then once that tank empties and I refill, I check how many gallons it takes and perform a manual calc just to see how far, if any, it is off.

I still find it odd that it just started doing this a few months ago.
Before this started, when I would fill up, I would usually see the Tank Avg to up to about 29-31 because I was getting right on the highway, and eventually settle to about 26/27 for the tank full by the next fill-up. I'm getting nowhere close to that now. Odd.

igzy

Yeah, it is likely due to cold weather for two factors:
1) engine will run rich in cold weather due to higher intake air density
2) winter gas blend which has butane as additive in it and this blend is not as energetic as summer gas and mpg will drop at least by 2% on average just for that

dreyfus

Nitrogen-filled tires are just as susceptible to pressure drop as every other tire. Regardless of what a salesman says, the laws of physics still apply.

In regards to your mileage dropping, my 2007 has 167,000 miles on it now. I have also noticed a fuel efficiency drop, but it has been over the course of time and not as quickly as you seem to have experienced. I chalked it up to engine wear.

Nevernu is correct that the built-in mileage meters aren't very accurate. Doing your own math will always yield better results.

craig72

You are correct. That was a dumb statement for me to make. I don't pay extra, that's just what Costco puts in them.

Regarding the computer calc, the Avg reading that I reset the other day has now settled in to pretty much match the Tank Avg on the display, right around 23mpg.

So I'm wondering if there is truly something else going on. I never really get into the throttle, but the other day I let it rip at WOT. There was definitely some hesitation there. It did not pull as smooth and strong as it used to.

Plugs and air filter are about a year old. Never replaced any coils or O2 sensors. Pretty much stock. Any thoughts?

oldgrump

Without the detailed reference data and other info from the Service Manual (or equivalent) your scantool numbers are not going to help you. As already suggested use the miles driven and actual amount of gas (use a major oil company premium fuel) added to the tank over several tankfulls to determine the average mileage. Something is not right, but the WOT hesitation/bogging on acceleration is not likely to have been caused by an O2 sensor issue. When near or at WOT the O2 sensor readings are not used by ECM. Did you have that issue before the spark plug change? Has there been any change in the idle speed, or the stability (no hunting/surging) of the idle speed? Any "hissing" sound (indicates a vacuum leak) when the engine is idling? The primary sensor used by the ECM to determine the correct amount of fuel to be "delivered" is the MAF sensor. Because of the obvious range of operation (the large changes in the amount of engine intake air) of the MAF sensor is one sensor that can start producing readings (when contaminated, for example) that may not be "seen" by the ECM as erroneous and the ECM does not set a fault code (with the associated illuminated Engine Check Light). Is the intake ducting between the air filter housing and the throttle body connected correctly? Did you notice a change in the color of the tailpipes (to a black, sooty color)?

ESh

Where to download those pdf files?
Also, where I can get repair manual for 07 ES?

Thanks.

nevernu

>>Where to download those pdf files?

Can't u just open them and save?

ESh

I can save those three, but I want them all (probably there are more than 3).

crwmlw

No doubt its the fuel, usually around October the stations carry the winter blend gas that causes a decent drop in fuel economy. Most people have no idea. Trust me this is it
http://www.ehow.com/info_12071245_lo...-blending.html