kapolani

iTrader: (6)

I just read a post where someone recommeded _not_ venting your crankcase to the atmosphere.

I followed one of the How-To's here - more specifically MalibuJacks home made catch can.

Is it detrimental because of the fact it allows unmetered air into the system?

kmcconn9

iTrader: (33)

Which line are you talking about. The PCV valve side of the breather side going to the intake.

You can vent the one going to the intake without problems, but not the PCV side. Even though many people will say they have done it for many years without problems....its just like all of the people with their boost gauge tapped into the FP regulator line that have never had problems.....dosent make it right or safe

Just keep the PCV valve hooked up, and you can either run the othe rline to the ground and let it drip, or put a breather filter on it...

l2r99gst

iTrader: (2)

This is probably one of the most overlooked problems because some people don't understand the operation of the PCV system or because they buy intake pipes from vendors like Buschur that tune mostly with speed density and don't use a MAF.

You should NOT vent your valve cover with a MAF based system. Let me explain why. I know I have explained this a few times in the past, but since this thread is dedicated to that, maybe it will be good for the archives.

Your valve cover has a PCV valve going to the intake manifold and a breather hose (straight through fitting) that connects to the intake pipe after the MAF.

Under conditions of vacuum in the intake manifold, like idle and cruise (anytime your boost gauge shows vacuum), the PCV valve opens. The vacuum from the intake manifold is used to scavenge excess cranckcase pressure, moisture, and gases to be burned back in the cylinders. The breather hose on the other side of the valve cover is there to provide clean, fresh, metered air after the MAF to mix with this mixture of moisture, crankcase pressure, gases, etc.

So, you can think of the path like this:

(1)Air comes in through your air filter, (2)through and counted by MAF, (3)through the breather hose, (4)into breather fitting, (5)through and under valve cover to mix with gases, (5)out of valve cover through PCV valve, (6)and then into intake manifold and finally cylinder to get burned.

The problem is that when you disconnect this breather hose and vent the valve cover from this fitting is that the air is now not metered. You are bypassing steps (1) and (2). So now your MAF has no idea of that extra air being consumed by your engine. So, you fueling will be lean. The front o2 notices this and corrects by making your fuel trims positive. How much positive depends on how much air is actually being drawn into your valve cover uncounted.

This is what messes up your fuel trims and why you shouldn't vent your valve cover with a MAF based system. You can still use a catch can in line with your breather hose, but the hose should be connected after the MAF to your intake pipe still.


Eric

SophieSleeps

iTrader: (19)

Fine. I'll go weld a fittig on it damnit

kmcconn9

iTrader: (33)

very interesting information. So how much leaner does it make your fuel tables.....enough to change the A/F?

A418t81

iTrader: (5)

It has no effect when you are in boost as the PCV valve is closed. It only affects, basically, closed loop fueling. I welded a breather hose bung onto the intake pipe that AMS includes with the 35R.

kmcconn9

iTrader: (33)

ah, well then this isnt my problem...for some reason I just started running lean 11.3-12.9 when I was running sub 11.1's

taenaive

iTrader: (20)

well, there is no problem doing that. it is just the emission device. Best way to do that is to remove the pcv and breather side all together and VTA . Removing just breather side will change the maf readings bit but that is when you are crusing and idling not when you step on the gas. also, stock ECU will compensate it pretty well for the cruse and idle. you don't have much control over closed loop operation anyway...
However, I didn't see any performance gain from it. Again, it only affects when you don't have any boost, Theoretically, removing those emission device will improve the power but there is too little to gain and your car becomes not street leagal. Also, under hood smell is awful .

kmcconn9

iTrader: (33)

man, there are so many opinions on what to do with the pcv and breather....

kapolani

iTrader: (6)

I followed MalibuJack's home made catch can how-to because I found some buildup inside my MAF pipe.

I haven't noticed any ill effects since doing it.

3gturbo

iTrader: (4)

I read a similiar thread somewhere and so I tried running the breather back into the intake after the maf. But it leaned out the afr and made it inconsistent so I put it back to venting to the atmosphere. It's my opinoin that on my car it is mostly venting air and not sucking in unmetered air this is also supported by the oil on the end of the breather hose filter. I'm not saying it doesn't suck in any air I just think that on my car it doesn't suck in much at all.

l2r99gst

iTrader: (2)

Under boost, it is a vent. That is why you build up oil in that line.

It's under vacuum where air travels the other way. This is what I explained above. It's only under vacuum that that PCV system is in operation.


Eric

kmcconn9

iTrader: (33)

so when under vaccume, how much, if any effect does it have on the A/F...estimated

l2r99gst

iTrader: (2)

Well, if your fuel trims aren't maxed out because of this, then your AF would go unchanged. When you are under vacuum, you are most likely under close-loop fueling. So, you aren't using your open-loop fuel maps. You are using O2 feedback with fuel trim correction.

The problem is that your fuel trims will get out of whack, along with the transition to open loop fueling. Your transitional AF ratios will be affected, but not likely your closed loop idle and cruise AFRs. Those will still be 14.7, unless you are maxing out your fuel trims.


Eric

3gturbo

iTrader: (4)

The biggest noticable difference was on the decel at a stop sign push in the clutch and the rpms would dip and the car would almost die. I have also been told to run that breather hose into the exhuast piping downstream of the o2 sensor. It's suppose to create a venturi effect and help suck the gases out of the engine any one have any thoughts to that approach?