Hey guys. I'm having some issues with my truck that I'm trying to get ironed out. I believe I made a mistake when I installed open breathers on both my valve covers AND a PCV valve with vacuum attached to it. I'm not sure whether or not my issues are related to this, but I'm curious if this is some of the reason I'm having tuning issues.

So I have an open breather on each valve cover along with the PCV valve hooked up to the intake manifold. The truck has been converted to mass air flow, so this would allow unmetered air into the intake manifold.

Question is what should I do with it? Unless I buy new valve covers, I pretty much HAVE to keep something covering those holes. I haven't seen a breather that does not pull in fresh air somehow, so I'm thinking that I should be able to plug vacuum off from the PCV valve and call it a day? Someone with more experience help me out with this one. lol. I'm having a tough time thinking today..

 

I haven't messed with a mass airflow system, but I made the mistake one time of putting a piece of tape over the oil filler hole on my 400.

The vacuum from the carb pulled about a quart of oil from the vavle cover in about 40 miles. Once I replaced the missing oil filler cap (vented) no more oil consumption.

Bottom line is if you have a PCV vavle in the valve cover, you need to make up the air from somewhere.

Robert

 

You seem to have created and solved your dilemma. Plug/remove the PCV system or replace the valve covers. You have, in fact, just created a substantial vacuum leak. Older non-PCV engines had to breathe through the valve covers. Once the crankcase was sealed (for emissions reasons) the crankcase was vented by sucking the vapors back into the intake and burning them ...... pcv. I don't see any reason for eliminating the PCV system and opening the crankcase to the atmosphere........ why? The 302 valve covers should be easy to find so I'd personally go back OEM.

 

It is vital that all air entering the engine be measured by the MAF sensor. This includes air for the PCV system. You need to cap off the breather hole on the cover with the PCV then remove the fresh air breather on the other. Mimic the factory method of supplying air for the crankcase by placing a feed line AFTER the MAF then over to the valve cover opposite of the PCV.

You have created a vacuum leak of unmetered air. You need some way of controlling the pressure in the crankcase a simple PCV will work, you just have to plumb it correctly.

 

OK, so the air from the PCV needs to be metered by the MAF, that would mean the PCV needs to be routed BEFORE the MAF in the intake, correct?

If that is the case, I need to redesign my intake. I built my own intake with an open element filter directly connected to the MAF. There is no way to plumb in the PCV there. A little more info on my engine..

I'm running a mustang Typhoon intake, so the PCV is in the back of the lower intake. I have some FRPP tall valve covers to clear my 1.7 roller rockers with a breather on each valve cover currently. I need to correct this obviously. So, what would be the problem with running no PCV, just the breathers? I have done some searching and found really the only solution is to do one or the other. Get rid of the breathers and connect the PCV to a spot where the MAF will meter it or plug the PCV vaccum and connect a short line with a small breather on the PCV to allow it to breath as well. Also, I'm not really seeing any advantage one way or the other. I know I've seen people say the PCV keeps negative pressure on the crankcase and that's great. It helps keep seals from leaking, but I've been running crankcase pressure to atmosphere for 4 years and over 100k miles on my diesel with no issues. Does anyone know any good reasons to keep the PCV???

I still have my OEM valve covers, but i will NOT put those crappy looking things on there. Let me see if I can find some nice covers for this thing that does not utilize the breathers.

pic for reference.

 

Keep the PCV connected to manifold vacuum. The air feed leading to the crankcase needs to be attached in the intake after the MAF in order for the engine to run correctly.

As far as requiring a PCV, that is subject to debate. I know the real go-fast guys usually use a header mounted system to create a vacuum for keeping the crankcase pressure down or the real serious ones use a dedicated engine driven vacuum pump. Keeping the crankcase pressure to a minimum or at a slight vacuum is free horsepower.

 

Ohhhhh. I understand now. I've never seen how the MAF trucks have the PCV run. That I could probably do. I'm going to see what valve covers I can find that look nice that will give me that option now. I need tall covers, but if I get much taller, they won't fit under the intake manifold. LOL.

 

Just vent the PCV to the atmosphere and remove the line that connects it to the intake manifold and plug or cap that port at the intake. Then, you can keep your breathers and valve covers the way they are.

 

I think this is what I'm going to do for now til I decide how I want to run it permanently.

Thanks everyone for the help. I'll go straighten it up and see how my tuning reacts now.

 

It's been my experiance with a hi revving motor(anything above 4500 for longer than a short time) without something pulling a vac on the crankcase, it will push oil out the breathers/oil dipstick tube.

As we all know a PCV looses that ability at any WOT situations, therefore, I would recommend a evac kit. I have used them on a couple different rigs with success. Last one I used the evac kit in conjunction with a PCV. As the evac kit doesn't pull any air at idle, or lower rpms.



Just a thought.

 

Dave!! I haven't seen you around in awhile. I'm glad you brought that up. The RPMs might be why I've never had an issue with my diesel venting to atmosphere. On it I run a single 3/4" hose to the back bumper venting crankcase pressure from the driver side valve cover. It only sees 4000 RPMs. My 302 is currently limited to 6200 RPMs. Once I have better valve springs or better heads, I will raise the limiter to 6500.

So, I just went and looked at evac kits. They all say that they can't be used with mufflers??? If that's true, I cannot use that. I'm going to vent the PCV to atmosphere tomorrow for now until I decide on my next move.

My options are, vent PCV to atmosphere and run two breathers, hook the PCV up correctly with the breathers pulling from the intake tube, or run an evac kit if they can be used with mufflers.

 

Factory mass air trucks have the breather connected to the intake tube between the mass air sensor and the throttle body, so its not metered.

 

Hmm..Every one I've seen, the PCV tube is connected on the Y/Plastic section, that's BEHIND the MAF Sensor...

At least that's how it was on the 96 truck I pulled the Intake Tubes off of, and made hybrid for my I6...And it's working wonderfully...

 

Your thinking backwards. The air is ENTERING the engine through the breather hose that is after the MAF, so that air has already been metered when it enters the engine. The PCV valve allows the crank case to vent into the intake manifold, so that air that is entering the manifold has already been metered b/c of the air that entered the engine through the breather hose. Make sense?? Air gets metered, goes through breather hose, into engine, back out PCV valve, and into the intake manifold to be burned.

 

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