New study shows 0 impact of a clogged air filter on fuel injected cars

[tangomar]

From EPA site:

http://www.fueleconomy.gov/feg/pdfs/...02_26_2009.pdf

It was instead (obviously) on carburetor cars.

[dremd]

THANK YOU THANK YOU THANK YOU!
I've been telling people this for years, and they have been telling me I'm wrong for years citing those cards on parts counters as evidence that I am wrong.

[Christ]

I always thought this was mostly obvious...

It's the reason I don't change my air filter, or just don't use one (instead, I use a T-shirt.)

[AeroModder]

The simulated clogged filter significantly affected vehicle performance, increasing the time to accelerate from 20 to 80 mph by 0.6 to 1.7 seconds on the three vehicles. The Outlet DP measured for each vehicle was sufficient for setting a common air filter indicator to the “change” or “clogged” position. For each vehicle, the Outlet DP at some point exceeded 5 kPa and showed an increase over the clean filter in excess of 2.5 kPa, a common standard for defining a dirty air filter.5,9–11
Despite the filter restrictions, however, no significant changes in fuel economy were observed. Each vehicle was run through at least three rounds of FTP, HFET, and US06 tests with the new air filter, and the same protocol was repeated with the clogged air filter. The tests were conducted on consecutive days for each vehicle. This format was used to allow for the required soak time to perform a cold FTP each morning. The resulting fuel economy data for the vehicles are shown in Figs. 3.8, 3.9, and 3.10. Range bars in the figures show the minimum and maximum of the tests for each case, while the columns show the average. Test-to-test repeatability is within about 1.5%, and all of the variances between the new and clogged air filter cases are similarly within about 1.7%. The baseline fuel economies for the vehicles were all within 0–6% of unadjusted EPA certification database values (U.S. Environmental Protection Agency) for similar vehicles.

Summary: In fuel injected cars, a computer monitors the air/fuel ratio and puts in less gas when you get less air, so FE isn't harmed, but performance is.

In carburated cars, a clogged filter alters the air/fuel ratio and degrades both performance and economy.

[Old Tele man]

...ain't it wonderful that computers are able to "correct & compensate" for lazy car owners (wink,wink)?

[doviatt]

So, does this also have a corollary effect on the discussions of ram air, and warm air induction?

[Jyden]

This would only be true for non turbo gas engines I belive. So keep your airfilter on your diesel og turbo car in good shape - clean that is!

[tasdrouille]

negative boost is negative boost, regardless of the engine type. The only difference is the carbed cars don't dynamically adjust fueling, that's all.

All this study is saying in the end is that even if your filter is clogged, the negative boost is never enough to have a significant impact on fuel economy when driven in normal conditions. A free flowing filter is always better, but so marginally better it's insignificant. Ram air reduces, and can even negate, negative boost, but again it's not much significant under normal driving conditions. WAI has ramifications in the combustion process itself so it's not just about negative boost in that case.

[Organic-Mechanix.com]

This makes perfect sense--The AFM only measures that comes into the unit through the filter, clogged or not. The fuel trims will adjust for the airflow and not be effected by the restriction before the monitoring device.

[Old Tele man]

...of course, all this "adjustment" is predicated upon the precision of the incoming measurement(s)...which are usually "close enough" at their design-center, but certainly NOT so at the edges/limits of their operating "ranges."

...Flex-Fuel vehicles, with their much WIDER-range sensors and computer algorithms, will probably be affected by this much LESS than the remaining 85% of the cars on the road (pun intended).