How to hook up PCV with EFI

[crutch]

I'm running Holley Sniper EFI on a 347 stroker with Edelbrock intake manifold and currently have my PCV valve hooked up from passenger side valve cover to the vacuum source on Sniper. The other valve cover with oil filter neck I have a filtered Air breather cap. I was doing research and sounds like I'm introducing unmetered air into the system with this breather cap. I've read a bunch of the forums and unclear how to hook up this other valve cover oil filter neck. I've seen some mentions of using a cap but doesn't the system need a source of clean air to pull through the crankcase? I've seen other mentions of needing a vented cap that gets clean air from after the MAF but where is that connection?

Can anyone provide clarity on this and a recommendation? Thanks!

 

[bigmuddy]

I can only speak to my FORD efi but this system the PCV gets air through the back of the intake, with both valve covers being blank. The only air coming in, is through the MAF and the TB.

I would simply find a way to plug off the other side with a fill cap and be done with it.

To that end be aware that any extra air that is not metered will create running issues. Not to say it won't run but will cause issues. I had capped off several unused vacuum sources with the cheap rubber chinese plugs and they all looked fine, they also didn't leak badly enough for me to see a gain in RPM checking with starting fluid. But when I would get on the throttle on the road they would suck air and create a nasty stumble. eventually I pulled them off and squeezed them and they looked like swiss cheese, When they were just on the engine they looked fine.. Go figure....

 

[Jebus]

I am not sure where the holley snipers air meter is situated, but the correct way, the factory way, is to draw in crankcase air after the air metering device. Any unmetered air into the system can not be evaluated by the fuel injection computer to adjust air/fuel ratio. The flow of the pcv valve is a variable. What does the holley sniper instructions say about this?

 

[crutch]

I am not sure where the holley snipers air meter is situated, but the correct way, the factory way, is to draw in crankcase air after the air metering device. Any unmetered air into the system can not be evaluated by the fuel injection computer to adjust air/fuel ratio. The flow of the pcv valve is a variable. What does the holley sniper instructions say about this?

I'll go back and dig through the sniper documentation but don't think it mentioned anything on this. I did search their forums. Someone else asked the same question and the recommendation was to vent that oil cap to the inside of the air filter.

 

[DirtDonk]

It's good to confirm with the instructions, but I believe that you have it correct currently.

You do need filtered incoming air to offset what's sucked out via vacuum to the throttle-body, but because this is not a MAF setup at least with a separate upstream meter, and your TBI is likely a Speed Density driven system, you do not need to be as careful where you put the plumbing.
The return air is not metered either through a valve cover mounted filter OR the main air filter housing with a typical TBI setup, so then swapping sources is not changing anything that I can see.

It can be a little cleaner going to the main air filter because valve cover mounted filter/breathers often weep oil on to the cover. But then so does just about any other fitting to the valve cover!
So if you're running either an air filter setup that's not easy to plumb a line to from the valve cover oil fill cap, or your current filter is not being messy, then keep the breather filter.

For those with a MAF setup, the vacuum is still sourced from a common area of the upper intake, and the filtered return is plumbed to the air intake system between the MAF sensor and the throttle body. Never behind the throttle body (that's full vacuum) and never through a separate filtered breather (that's the un-metered air under discussion here).

Paul

 

[Steve83]

The fuel system doesn't really matter - the PCV system is just air, so it works the same for all engines. Read this page:

(click this text)

 

[Broncobowsher]

Sniper gets PCV just like a carb.

Sniper does not have a MAF sensor, it is a speed density based system. So there is no air meter to bypass.

Short answer, what you have now is correct. Fresh air in one valve cover, PCV valve metered pull out the other valve cover.

 

[crutch]

Thanks everyone for the feedback. this is very helpful and makes more sense now!