PCV valve for EFI conversions?

tbitz · 08-27-2006, 08:59 AM

A lot of the guys converting to EFI are cutting up the airbox and removing most of the CIS components.

One component being removed is the hose going from the CIS intake boot to the OIL filler tube.

It's been a while since I was running stock CIS, but I recall there was a small vacuum when opening the oil filler cover. This vacuum , I believe, helps suck out gases in the crankcase (ie: combustion gases that make it past the pistons and into the crankcase).

In most EFI conversions, the hose from the oil filler tube to the CIS rubber boot is removed and there is no vacuum going back to the crankcase. I wonder if this may lead to problems down the road?

Perhaps a small PCV valve needs to connect the crankcase to the vacuum side of the airbox.

I thought I'd bring this up for discussion since alot of folks are converting to EFI these days.

Cheers,

DUK · 08-27-2006, 09:28 AM

Subscribing to this thread. I just looked at this a couple of days ago.

Scott R · Scott R's Garage

I want to see how this comes out as well, I just purchased a second airbox to modify.

rfuerst911sc · 08-27-2006, 11:10 AM

Here's what I did on my conversion with TWM throttle bodies. I took the charcoal cannister in the engine compartment and removed the charcoal. I then took a fitting the same I.D. size of the hose you are talking about and screwed/epoxied it into the side of the cannister. I also added at the lowest point a simple brass drain fitting. Last I added a small K+N filter so it can breath. So if you can picture this the oil filler neck hose goes to the cannister and the OEM fuel hose from the tank also goes to the cannister. I then ran a hose to one of the air cleaners so I am thinking any fuel fumes from the tank will be burned along with any oil vapor. It sounds complicated but it's real simple and looks stock. And with the drain valve I can drain oil residue if it ever builds up.

tbitz · 08-27-2006, 12:14 PM

Quote:

Originally posted by rfuerst911sc
Here's what I did on my conversion with TWM throttle bodies. I took the charcoal cannister in the engine compartment and removed the charcoal. I then took a fitting the same I.D. size of the hose you are talking about and screwed/epoxied it into the side of the cannister. I also added at the lowest point a simple brass drain fitting. Last I added a small K+N filter so it can breath. So if you can picture this the oil filler neck hose goes to the cannister and the OEM fuel hose from the tank also goes to the cannister. I then ran a hose to one of the air cleaners so I am thinking any fuel fumes from the tank will be burned along with any oil vapor. It sounds complicated but it's real simple and looks stock. And with the drain valve I can drain oil residue if it ever builds up.

But this isn't creating a vacuum in the crankcase.

I think a vacuum is needed to suck out the combustion gasses which would otherwise end up the oil.

The other thing I was thinking about was that if the crankcase has a vacuum (ie: lower pressure than atmosphere), it may help reduce oil leaks. The reasoning is a vacuum in the case would "suck back" any oil trying to drip through a small hole in the seam of the case.

tbitz · 08-27-2006, 01:48 PM

I currently have a small K&N air filter mounted directly on the oil filler tube as shown here:

I took the small airfilter off and hooked up a hose from this location to the fitting that used to have the AAR valve which is now plugged.

Here is the AAV fitting location which is currently plugged:

In the middle I put the old CIS resitrictor. This isn't really a PCV valve, it is more like a filter with a small hole to limit the amount of air flowing.

Here is a picture of the CIS restrictor.

Started the car and it ran. The vacuum though is waaaaay to much. I could barly get the oil filler cap off due to the strong vacuum. Also I heard the plastic oil resivoir slightly collapse as the engine started. It also popped back out when the engine shut off.

Seems like a lesser vacuum is needed. In CIS the hose was hooked up above the throttle body, but before the CIS metering plate, which had a very slight vacuum.

I will try something else and post results.

cmonref · 08-27-2006, 03:53 PM

The old AAV fitting goes to the starting injector location which then introduces air below the throttle plate. As you note, the CIS hooked the oil tank breather to the boot between the metering plate and the throttle. Other cars hook the breather just downstream of the filter.

I always figured the hole in the CIS restrictor was intended to let air flow but to keep oil that has condensed on the walls of the hose from entering the intake boot.

tbitz · 08-27-2006, 04:41 PM

I looked at my Saturn Wagon and one side of the PCV valve is hooked BELOW the throttle plate and the other side goes to the valve cover.

With this setup the crank case is at full vacuum.

tbitz · 08-27-2006, 05:03 PM

Found a link that discusses the operation of the PCV valve.

http://www.filtercouncil.org/techdata/tsbs/94-2R1.pdf

Europa Auto · Europa Auto's Garage

I left both oil breather connections from the air boot to the oil filler hose in tact during the installation of the EFI kit and its been running just fine.

jbrinkley · 09-01-2006, 05:10 PM

anything new Mr. Tony? my hoses are cut with a tiny filter. I'm getting a small amount of smoke wafting up out of the filter and cap when I check the oil.

tbitz · 09-01-2006, 10:05 PM

Looks like the best bet is to hook up the breather hose above the throttle plate where vacuum is very little, but enough to suck the gases out, just like it was with CIS setup.