Reasons to/not-to use K&N breather filters

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on fuel injected cars...

Can anyone name some?

The breather filter I am referring to is part of the PCV:

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Its on the LEFT of the pic on the LEFT cam cover.

The engines in question are modern MPFI OHC V8s that have a butt load of sensors and computer stuff.

So far I've heard that using a K&N breather will allow unmetered air to enter the engine (not good for OBD-II computers) as well as allow dirt into the engine DIRECTLY considering the age-old K&N vs Paper argument.

Then I've heard that its ok to use these becuase it doesn't matter if unmetered air enters the engine.

Modern MPFI engines normally use a tube that allows the crankcase to suck in air for the PCV system via the main air inlet tube - which means that the intake air has already been accounted for by the MAF.
 
Uh, it won't let unmetered air into the engine if you plug up the port on the intake where the PVC line hooks to. Many people do that, remove the PCV valve and stick a breather filter in it's place. They think that's going to help out by not letting oil/oil vapors from contaminating the intake tract, because the PCV works of engine vacuum. Which is exactly why you want to KEEP your PCV valve setup. It will use engine vacumm to suck out blow by gases from the crankcase, where as, if you just stick a breather filter in place of the PCV valve, it will vent the crankcase but there's no vacuum to expell blow by gases. PCV valve = good. Breather in place of PCV = bad
nono.gif
. Please, if someone disagrees, correct me if I'm wrong.
 
So would it let unmetered air into the engine if the PCV WASN'T blocked at the intake?

What I'm asking is - would it let unmetered air into the engine IF you replace the breather cap/tube with an open air K&N-style breather filter but keep the rest of the PCV system stock?

I'm saying yes because the air that normally goes into the crankcase comes from the air inlet tube that receives metered air.

for those tuning in: carb'd cars do not apply in my argument because carburetors don't give a hoot about sensors
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Yea, if you don't cap off the line that goes from the PCV valve to the intake pipe (most cars, it goes into the flexible rubber pipe between the throttle body and the air meter), your car won't even run. It's like having the biggest vacuum leak you could have because the engine is now sucking in air past the air meter. At full throttle, it wouldn't make a difference, but part throttle driveability would be gone. On my car, if I remove the hose off the PCV valve while the car is idling, it sputters and dies instantly.

Are you considering doing this or something? I wouldn't. The stock PCV system is fine. It will eventually contribute to more gum and varnish on your throttle body and inside your intake manifold, but you can solve that in about 10 seconds with some throttle body cleaner.
 
I was against this idea from the start but some older folks who have carb'd cars on another forum insist that letting unmetered air into the engine wouldn't be a problem.
 
if u put a breather u will have many long term affects...one is oil sludge build up...soem people put a breather for performance but really it hurts the engine really bad....i can go on and on but really one word summarises it all..NO.
 
If you plug the PCV air tube inlet, the engine will run slightly leaner, because slightly more air is going to the throttle body. I think the effect would be countered by the O2 sensors though. They would sense the leaner mixture and compensate for it.

I too would leave the PCV system as it is. It works very well, and helps to prevent detonation.

I have a K&N breather on my carbed Bronco (same setup as in your diagram) and it works very well. The air is metered through the PCV valve itself, so driveability is not affected.
 
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