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Unread 03-24-2009, 03:30 AM   #1
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Default New study shows that replacing a dirty air filter does not improve MPG

Quote:
NEW INFORMATION:
Replacing a Clogged Air Filter on Modern Cars Improves Performance but Not MPG

Air Filter:
A new study shows that replacing a clogged air filter on cars with fuel-injected, computer-controlled gasoline engines does not improve fuel economy but it can improve acceleration time by around 6 to 11 percent. This kind of engine is prevalent on most gasoline cars manufactured from the early 1980s onward.

Tests suggest that replacing a clogged air filter on an older car with a carbureted engine may improve fuel economy 2 to 6 percent under normal replacement conditions or up to 14 percent if the filter is so clogged that it significantly affects drivability.

The effect of a clogged air filter on diesel vehicles will be tested in the near future.
http://www.fueleconomy.gov/feg/maintain.shtml

So what do you guys think about this? This seems to go against nearly all of the studies I have seen regarding air filters and their effects on fuel economy.
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Unread 03-24-2009, 11:35 AM   #2
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I've believed that for years but never wanted to get into a debate!

On a carbed engine, a clogged/restricted intake intake (air filter) will draw more fuel from the carbs jets by way of increasing the vacuum due to the restriction.

On a fuel injected engine, air flow rather than engine vacuum dictate the fuel mixture. And the Oxygen sensor will watch the fuel mixture and make adjustments to keep the mixture ideal. However, air flow is reduced and will limit the power available.

I've pulled air filters out of FI engines with clean and nearly overly lean spark plugs. That same air filter would have choked a carb engine and fowled the plugs.
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Unread 09-11-2009, 03:32 AM   #3
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Thanks for the information.

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Unread 09-11-2009, 01:18 PM   #4
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Quote:
Originally Posted by Mr Car Guy View Post
I've believed that for years but never wanted to get into a debate!

On a carbed engine, a clogged/restricted intake intake (air filter) will draw more fuel from the carbs jets by way of increasing the vacuum due to the restriction.

On a fuel injected engine, air flow rather than engine vacuum dictate the fuel mixture. And the Oxygen sensor will watch the fuel mixture and make adjustments to keep the mixture ideal. However, air flow is reduced and will limit the power available.

I've pulled air filters out of FI engines with clean and nearly overly lean spark plugs. That same air filter would have choked a carb engine and fowled the plugs.


It will still effect the FI engine's mileage, but in a much more indirect manner.


The power loss will make the driver apply more throttle to compensate for the loss of power. This is what kills the mileage on an FI engine.
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Unread 09-11-2009, 02:11 PM   #5
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OK, more oxygen = bigger fire. Why the hell does this make sense? Is there a way to modify the OXY sensor?
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Unread 09-11-2009, 03:08 PM   #6
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Quote:
Originally Posted by TestECull View Post
It will still effect the FI engine's mileage, but in a much more indirect manner.


The power loss will make the driver apply more throttle to compensate for the loss of power. This is what kills the mileage on an FI engine.
Yup...that's my kind of logic.

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