When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Hey, I inherited this setup from the previous owner. I took a close look asst how they setup the catch can, and it seems incorrect to me. It doesn't look like any of the pictures I can find, and seems like it would cause a vacuum leak.
As you can see, the line from the driver's side head with the PCV on it isn't even routed through the catch can. It just goes into the intake like stock. The smaller line coming off the passenger head goes into the catch can, and the can itself has a breather. Now if I understand correctly, this will suck unmetered air through the catch can breather, into the passenger head, through the crankcase, out the driver's side head, and into the intake. So basically the catch can is doing nothing but causing a vacuum leak, right? That would explain why it's ALWAYS bone dry.
Did some more looking this morning. I guess my throttle body has been adapted from some later LS engine. Looking at the notes the PO gave me, it looks like it's an LS2 TB. It doesn't have the little metal nipple coming off the throttle body for the front passenger breather, so I'm not sure how to correct this. I'm guessing it doesn't go to vacuum since that wouldn't cause a pressure differential, so no air would move.
It looks like the air bridge has a couple bungs that are currently plugged. I'm thinking of just routing the breather tube up there and eliminating the currently catch can. If I understand correctly, this will make the PCV system run like stock and eliminate the vacuum leak.
Alternatively, I could run the PCV line into the current catch can and cap off the bung on the intake manifold. No more oil ingestion, no more vacuum leak, but the crankcase wouldn't be pulling a vacuum.
the line running to that can is just venting crankcase pressure to the air, no vacuum leak. that's really a breather. looks like your pvc is working like stock, the pass. side valve cover has been vented to air, normally that line is tied to the pvc
But if the crankcase is pulling a vacuum from the other lines, isn't it going to be sucking air from the breather? The stock system is designed to be closed.
correcting my first post, the pass side valve cover line goes to the throttle body. The vacuum is created at the intake, the crankcase is under pressure pushing air out. that can isnt creating a leak
I started the car, let it idle, and put my thumb over the line that's going to the catch can. There is definitely some vacuum there, but it's fairly weak.
I just don't follow your explanation. If air is flowing from the crankcase to the intake manifold, where is that air coming from? It would seem to me that it has to be coming from that breather line. In the stock setup, it hooks up to the throttle body AFTER the MAF, so all the air is metered. The way mine is setup, the small amount of air that's entering is unmetered.
I'm not sure if the flow would increase or decrease with RPM. I know vacuum decreases, but the PCV also opens up.
Is there more than one line going to that can? The line coming from the valve cover should have pressure not vacuum. the crankcase produces pressure not vacuum, the vacuum in a pvc system is produced thru the intake evacuating the pressure buildup in the crankcase
Here's a diagram I found of the system. The blue lines are hooked up like stock, and would be pulling a vacuum since they're connected to the IM. The green line is the line in question. looking at the flow direction arrows, it seems like it's pulling filtered and metered air from before the throttle plate, through the crank, out the two read breathers, through the PCV and into the intake manifold.
Unless I'm completely misunderstanding this diagram, this would create a leak. At the very least, this catch can isn't doing anything.
O.k. I think I understand what you have there from the diagram, that is hooked up to the clean air side of the pvc, that line would be hooked to the throttle body(2001 -2003) or the air bridge(2004), but it is just sucking clean air thru that breather. That is normally not non metered air. no leak
Ok, good deal, so we do have a problem then? So back too my previous question. My TB doesn't have the nipple for the green line to attach to. Should I just eliminate the catch can entirely and run the green line up to one of the plugged bungs on the air bridge and run like stock? Or should I disconnect the PCV line from the IM, cap that off, and run everything to the catch can?
With the first solution, I'd get the benefits of the having the crank ventilated. With the second solution, the crank isn't well vented, but I'm not pulling any oil into the IM. (I've had the intake manifold off, and it's definitely sucking some oil, but that's to be expected with forged pistons I believe.)
Either way, I plan to get a proper catch can eventually that'll keep the system closed and the oil out of the IM.
no problem, that can is not functioning as a catch can. That line would need to be plumbed into the air bridge. Go to elite engineerings web site, they have great instructions on how a catch can should be plumbed.
Catch can hooked up wrong?
