vibe/matrix gas mileage problems

If you have the defrost on all the time the AC is running too, if the outside temp is over 32 F. That could kill your millage. I live in CT and the past couple of mornings I've had to use the defrost to clear the windows. I was used keeping on all winter long in my old Tercel.

John

Thanks for the quick reply. I'm aware that the defrost automatically kicks on the AC. Haven't been running the AC or defrost very much. My main concern is that I've never gotten mileage this low in my Camry, even loaded heavy with the AC on! Andy

The A/C compressor won't run if the temeprature is below approximately 40 degrees F even if you are in the defrost mode (even if the system normally runs the A/C in defrost mode). At low temperatures the A/C cycle ceases to work and the compressor is shut down.

Ed

I suspect you need to take your data more carefully.. Unless there was something horribly wrong with your Camry, there is no way a K&N filter should have any measurable affect on fuel economy. Fuel injected engines are not adversely affected by air filter restrictions like old carbureted cars were. For a fuel injected car, there is very little difference as far as the engine computer is concerned between a restricted air filter and a slightly more closed throttle. K&N filters might (but probably don't) provide more high end horsepower if the OE filter is poorly design, but there is no way they are going to improve the mileage of a recent fuel injected vehicle by 2 to 3 miles per gallon (unless there was something horribly wrong with the OE intake and filter).

Other possible reasons for lower than expected fuel economy include using one of the various reformulated gasolines, dragging brakes, incorrect odometer, poor mileage calculations. You need to record gas purchased for multiple tank fulls and compute an overall average to get a reasonably accurate estimate of your fuel economy. Single tank averages can be very misleading. And finally, if you are doing mostly city driving, averaging 26 mpg versus an EPA estimate of 30 is not that unexpected. City mileage is particularly dependent on driving style. Maybe the Vibe encourages spirited driving? And exactly which model Vibe do you have? One 2003 sports model is only rated 25 city / 30 highway (and requires premium fuel). And in fact none of the 2003 Vibes are rated better than 29 / 36. So, you need to verify your model. It is possible you are actually beating the EPA estimates if you have a Sports model.

Ed

Ed, If you read my original post, you'll note that I have a 5 speed manual transmission, BASE model Vibe. The "Sports" model is called the GT, and it has a 6-speed manual transmission. Also, regardless of calculations, gas formulations, number of tanks calculated, or whatever, the fact remains that my Camry has never gotten less than 27mpg (usually 33+mpg highway), when the EPA says it should get 23/32, and my Vibe has never gotten more than 26, when the EPA says 30(or 29)/36. Both manual transmissions, same calculations, same gas, same commute, and (as close as I can tell) same driving. I know the EPA estimates are not necessarily real-world scores, so let me restate the question: Why is my Camry 20% above the EPA city estimate, while my Vibe is 10% below? Did their estimates really change that much in 5 years? I wondered also about the odometer being off - how often does an odometer "go bad"? I did put on new tires, but I calculated the circumference to be within 1cm of the old tires, which should change the odometer reading by half a percent or less. I'll try to test the odometer by driving the same route in both cars and comparing readings. Regarding the K&N air filter, I did calculate mileage over several tanks of gas both before and after I installed the filter on my Camry, and mileage was consistently at least 2mpg better after. If that means there was something wrong with my old air filter, so be it. In that case, there also must have been something wrong with the old air filter on my mother's '00 Camry, and my father's '03 F150, because mileage on both of those vehicles consistently increased as well after the addition of K&N filters.

Andy

Keep in mind that without examining both vehicles and measuring results with you driving on a dynamometer, all anyone can give you are guesses.

I'll give my guesses.

The odometer on one or both cars could be incorrect. Check accuracy by using the mile markers on highways over a 5 or 10 mile stretch. Inaccuracy can be caused by differences in tire diameter as well as by an internal problem with the odometer. If I were to guess, I'd say that the Camry's odometer is overstating miles traveled.

Another possibility is that the driving style that has resulted in very good fuel mileage in your Camry does not neessarily work as well for the Matrix. The Matrix has a smaller engine and so later shifts may be necessary to get the same performance and/or fuel economy as the Camry because the Matrix's engine is lugging a little bit.

Did their estimates really change that much in 5 years?

The methodology for determing fuel economy has not changed that much in the past 5 years but I believe that it will change soon to more closely reflect real-world dirving conditions and will probably result in lower fuel economy estimates.

Very rarely in a Toyota. In fact, I have never run across one, although accuracy can very as much as 10% over or under.

I did put on new tires, but I calculated the

Try measuing the circumference of the tires instead of calculating them. Your suggested test is a good one.

K&N and other "high performance" air filters may improve fuel economy and performance, but bear in mind that in order to improve air flow, the passages are not as fine so they have a tendency to allow more contaminants to pass than a conventional filter. More contaminants means shorter engine life and more frequent oil changes required. The filters that are soaked with oil can also have an adverse affect on MAP/MAF sensors. For this reason, I am not a fan of "performance" air filters for normal street use.

Thanks for your guesses! I'll take them into consideration. Andy

Andy: When I bought my Corolla new back in 2003, it got considerably less than EPA mileage for the first 2,000 miles. The car didn't start getting close to EPA until it had 6k miles. And it wasn't until nearly 15k miles that it would meet EPA mileage on occasion.

With the manual transmission, you DO need to limit engine rpm to no more than 2500 and keep your foot out of the throttle to get those EPA mileage figures.

We've been tryin t'tell you Andy...Toyotas rule! :)

You're welcome!

So why did installing a K&N Air Filter result in the mileage increasing? How does the engine tell the difference between the restriction of a paper air filter + throttle plate and the restriction of a K&N air filter plus throttle plate? With modern fuel injected engines, the amount of fuel injected is adjusted by the PCM based on the oxygen sensor reading. If less air gets into the engine less fuel will be injected. The amount of air inducted into the engine is controlled by the air restriction in the intake tract. This restriction is a combination of the air restrictions of the intake tract, air filter, and throttle plate. If you lower the restriction presented by the air filter, you'll just close the throttle a little more to arrive at the same overall restriction. The PCM has no idea whether the restriction is a result of the air filter or the throttle. There is no basis to believe that a K&N filter should increase fuel economy for a modern feedback controlled fuel injected engine. In the old days of carbureted engines, air filter restrictions would affect fuel economy because the increased restriction would act like a choke and richen the mixture.

So why do people report increases in fuel economy with K&N air filter. I have a few theories:

1) Wishful thinking - they want it to show an improvement, so it does 2) Poor fuel economy measurement - most likely cause 3) Induction noise changes because of the change in filter and people drive more slowly because they confuse noise with power 4) K&N was installed as part of a general tune-up 5) People modify their driving style after the installation because they installed it as part of an overall desire to improve fuel economy 6) The reduced restriction does actually screw up the sensors and this results in a leaner mixture which actually improves fuel economy. This seems very unlikely unless things really get out of whack, The PCM should adjust the fuel trim based on the O2 output, but I suppose minor improvement might be possible - but certainly not the 10+% you are claiming. If Ford, or GM, or Toyota thought they could increase fuel economy by 10% by just changing air filters, they would. And they would not have to use a K&N to do it - just a much larger paper filter. From calculations I have done in the past, most US vehicles already come with air filter substantially larger than necessary to provide a minimum air filter restriction.

GOOD post, CE White! I agree with your 6 points.

C. E. White wrote:

Well, one thing you are forgetting (although you did mention it) is the term "feedback system" (it's a reactive system, not proactive). So what is it feeding back to? A hard coded fuel map based on throttle postion, temperature, etc. Fuel injection is really not that far off from the carbs of old (which is why there is little mileage improvement when you compare most modern FI engine over their older carbed brethren). The fuel map determines how much fuel at any given throttle position should be injected and the feedback sensors (MAF/MAP and O2 and probably some others like IAT) allow the computer to trim the fuel for emissions as required. But the fuel map is what determines the injector pulses and overall amount of fuel. So if a filter allows more air in, then that "should" require less throttle. And at less throttle, the map is going to assign less injector pulses and then trim from there. I'm guessing the reason some people see improvements and others don't is more a factor on how restrictive the factory intake setup is (twists, turns, etc.) and maybe even whether the factory sized filter is adequate or not. But the bottom line is many, many people report SOME type of improvement overall in both power and mileage and I'd be hard pressed to say they are all just imagining it. My conclusion would be that there are some benefits to the filter, and each person must decide if the cost is worth the gain.

I had an '81 350cid (5.7L) Chevy pickup that got 20mpg with a 4 barrel carb and 3 speed tranny, yet my '04 262cid (4.3L) S10 with modern fuel injection and a 4 speed tranny is lucky to see 18mpg on that same highway...go figure.

Todd