AJsArmor

When I ditched the EGR setup yesterday I was looking at this pic...



And got to thinking, "is this right?" in reference to the little filter I put on the valve cover. By that I mean is it doing more harm than good? The PCV valve at that back of the valve cover is basically a one way valve, allowing air only to pass away from the cover and into the intake housing since there is a vacuum present from it. Since there is only a filter on the front fitting, basically isn't this like having a vacuum leak? There's no metering of the air flowing from the filter, under the cover and into the intake. Could explain my CEL of code 5 "oxygen sensor lean/rich" as it's allowing too much air to pass?

I just routed it back to the intake to the fitting with the black cover, see if I notice a difference and if the CEL goes away. I did already notice I had to adjust the idle.

iamsuperbleeder

why not just get another little filter and attach it to the PCV valve?

well, don't do that without some facts 1st; I don't know if that'll screw up the system or not, lol

personally, I'd just leave the PCV system stock, unless someone on here can post a tryed and tested upgrade of bypassing it...

abecedarian

the breather/filter IS causing a vacuum leak. unmetered air (air that has not passed through the AFM) is being allowed to enter the intake manifold, and the ECU is unaware of it so your fuel mix will be lean.
there SHOULD be a hose from the valve cover (where that filter is) to the throttle body, the fitting the 'white' tape or whatever is covering, just behind the clamp around the boot for the intake duct.

AJsArmor

I just rigged something up to replace that and unplugged my battery. See what happens and hopefully that'll stop the CEL too.

long-haul

I have the same filter + PCV setup and worry that Abe raises a fine point about a vacuum leak. Would the same leak cause a similarly lean condition with my Weber that it would with your EFI?

If yes, where should I route a vacuum line? Do any Weber guys have suggestions/pics?

Thank you-- very sorry for the hijack.

abecedarian

if the pcv valve vents into the intake plenum, either after the throttle body for an efi vehicle, or between the carb and head for a carb'd vehicle, and the fresh air inlet to the crankcase bypasses the afm/maf (for an efi vehicle) or the carburetor (carb'd), it will create an unmetered air vacuum leak.

long-haul

Thanks amigo- the way you put that really does help me understand better. I wonder if the filter/tower/chrome-plated-waste-of-$$ shouldn't be connected to the carb somehow.... I went through all of this when I did the Aisin to Weber carb conversion but here I am re-hashing the same thoughts 1 year later... Are there any Weber guys online with (free) advice?

Pistonman

It is easier to adjust for the extra air with a carb. You need to read your plugs, along with driveability. What jetting are you running? On my Weber setups I use a Carter 4070 pump, (with a relay and breaker) and a Holley low pressure fuel regulator set at 2.7 psi. Weber carbs do not like alot of pressure.

Swansen

Here is a thread on the PCV valve vs filter, also has info about a catch can. The PCV valve is debated like the ERG valve is. https://www.yotatech.com/forums/f116...eather-141274/

abecedarian

and another side note:
if the pcv system cannot vent properly, the crankcase will build positive pressure, and force oil out through any possible point including the front and rear crankshaft seals, around the valve cover and anywhere else not positively sealed, including out through the neat little filter in the original poster's pic.

drew303

I could see how that could confuse an EFI setup but I'm wondering how it causes a vac leak on a carb setup.. I'm not familiar with 22RE's just R's...

on the 22R it just connects into the intake, on the carb this is just basicaly atmosphere. The motor runs with it or without fine. Nothing changes. I only see it working as a neutral vent? Where as the PCV is pulling pressure to eliminate it all together.

But don't the 22RE's run like crap with the oil cap removed.. as 22R's aren't effected.

drew303

Did a little reading... The front vent is the clean air vent for the whole engine. It's suppost to allow air into the engine/crank etc... So... how does unplugging it or putting a vent on make the engine perform differently or cause a vacum leak?

The engine itself isnt a sealed container, the pcv only pulls out what it needs to keep the pressure inside the engine neutral or same as the outside atmosphere. As blowby occurs pressure increased, pcv opens with a positive vac to take it out. A controlled vac which explains the valve.

I read that back in the day, the solution was just a vent tube, no vac no pcv.

correct me if im wrong

Swansen

seriously though, read that thread in that link, it answers all of your questions.

AJsArmor

In my pic you just have to follow the flow of air to understand how it's a vacuum leak. The PCV valve is a one way ball valve, allowing air only to pass out of the valve cover and into the intake plenum. Of course it does this because the intake is pulling a vacuum. Now with the filter on the front like I have in the pic, air is just sucked into the valve cover and through the PCV valve unregulated.

It's no different than if I took that rear vac line off and put the air filter on the end of it, it's a vac leak, only filtered. The setup I had it just allowing air to be sucked into the intake like a vac leak, made a difference in my idle when I undid it.

long-haul

Pistonman- I use a Napa mechanical fuel pump and one of Summit's fuel pressure regulators set to 5# because any lower and the truck dies off in 3rd gear. Jetting is as follows:

primary/secondary
idles 55/50
mains 135/140
airs 170/170

I am a total rookie at plug-readin' but for driveability I have never heard pinging but I do smell gas at idle. The truck stumbles a bit if I stand on it from idle.

Would this exacerbate the unmetered vent up front? Does the jetting look pretty standard?

Pistonman

long=haul, pm sent.

abecedarian

If you look at the pic, it's obvious how it can become a vacuum leak. You have the full intake manifold vacuum applied directly on the PCV valve. When the pressure in the crankcase is sufficiently high (which isn't really 'high' since you have negative pressure {vacuum} on the intake side of the PCV), the crankcase gasses are vented directly into the intake manifold.
So then, you have to consider what happens when the crankcase 'vents' into the intake and needs some extra "air" to equalize the pressure.... On the 'standard' EFI system, it pulls filtered air in from just in front of the throttle plate (on someearlier models, it pulls air in from behind the throttle plate) which means that every bit of oxygen / air that enters the crankcase has passed through the intake air filter and the air flow meter, so there is no 'unaccounted for' air entering the crankcase.
Putting the filter on the valve cover, like in the pic, means that air can enter the crankcase, and then the intake manifold, without ever being 'measured' by the fuel injection system, thus causing erroneous air/fuel mixture readings that can only be compensated for when the O2 sensor reports in.