Significant decrease in fuel economy - Smart Car of America Forums : Smart Car Forum

NCC1701 · 07-31-2010, 07:39 PM

Ok, I know it's Summer (believe me I know

). But, I'm wondering if any of you think I might have a problem, and if so, what it could be. Check out these graphics, including my latest fuelups at fuelly.com

Even my overall average at 93 fillups has dropped by 0.4 MPG, after being rock steady on 35.0 for a year. I'm thinking that that much of a drop in a 2 year average might be cause for concern. My July average is almost 5 MPG lower than last August's average.

**rfernatt** · 07-31-2010, 07:44 PM

That is odd... No recent changes in your typical driving environment (driving uphill both ways?), the car itself, or your driving habits?

The typical possibilities like restricted air filter, restricted exhaust/catalytic converter, mechanical drag (parking brake issues), etc. come to mind.

NCC1701 · 07-31-2010, 07:50 PM

<slaps forehead> Air filter! It likely is overdue for cleaning. Could that alone be the cause? I haven't really noticed any decrease in performance. No more than any other A/C on in the past performance.

**rfernatt** · 07-31-2010, 07:57 PM

I wouldn't think an air filter alone would be that dramatic and that sudden. You'd probably have seen it slowly dropping off over time, but it certainly wouldn't hurt to check/change it.

Also, do you typically get gas from the same station? Have you changed stations lately? If not, maybe you should try a different station for a couple tanks.

Still using original spark plugs or have they been changed?

If you can't find anything else to check or try, you could try disconnecting the battery and let the ECU revert back to its stock state and see if it makes a difference.

Kermit · 07-31-2010, 08:03 PM

Same thing has happened to me NCC. Of course I added bigger wheelss/tires too. I could swear the road is stickier due to the asphalt being so hot, that and heavy A/C use could be a factor.

**rfernatt** · 07-31-2010, 08:08 PM

Quote:

Originally Posted by Bum-bling-B

Same thing has happened to me NCC. Of course I added bigger wheelss/tires too. I could swear the road is stickier due to the asphalt being so hot, that and heavy A/C use could be a factor.

Could be... Is it really that much hotter than last year or earlier this summer?

bluedeuce · 07-31-2010, 08:13 PM

Let's check off the usual stuff:

* have you run the AC a lot lately?
* check your tire pressures
* clean/replace the air filter
* if you hit a big pothole or critter, check the alignment
* could be a batch of bad gas/wrong gas
* pump clicked off early
* are the O2 sensors still plugged in?

Kermit · 07-31-2010, 08:14 PM

I don't know about Panama City, but we cleared 100 today just a few miles up the road. Yes, it is hotter.

NCC1701 · 07-31-2010, 08:16 PM

Quote:

Originally Posted by rfernatt

I wouldn't think an air filter alone would be that dramatic and that sudden. You'd probably have seen it slowly dropping off over time, but it certainly wouldn't hurt to check/change it.

I've got the Breathless Performance filter. Could need cleaning. Actually, it's never been cleaned since BBB installed it, and I don't know precisely how to do it. I can research it though.

Quote:

Also, do you typically get gas from the same station? Have you changed stations lately? If not, maybe you should try a different station for a couple tanks.

Whenever possible, I go to the same station, and the same pump at that station.

Quote:

Still using original spark plugs or have they been changed?

I'm not sure. Isn't a spark plug change part of the 20K scheduled?

Quote:

If you can't find anything else to check or try, you could try disconnecting the battery and let the ECU revert back to its stock state and see if it makes a difference.

Stock state?