PCV - Catch Can - Vacuum Pump

Gandalf · September 22, 2022

I am very happy with my new-to-me 2015 sierra 1500 (5.3 l) All-Terrain, and especially happy to be back to wrench-twisting a bit on weekends - after I sold my beloved 1973 Ford 3/4 ton 20 years ago, I’ve had only small commuter cars. Since March, I’ve done front/rear gears (4.56s for the 35 inch tires and 8 inch BDS lift), Timbren suspension rear, large capacity transmission pan, new tranny bypass valve, and a few other things.

However, from my time on here, I’ve become extremely worried about coking valves, due to the GDI engine. I’m on a quest to make sure that absolutely no unburnt gases, acids, water, etc., ever reaches the back of the valves again. It’s a better engine than the LS, except in this one area, and I think I’ve “solved” the problem, except for one thing:

I deleted the vacuum pump, but left it on the block, until I make the next decision - can I route the PCV valve line to the vacuum pump, with a catch can in line between the two, thereby creating vacuum for the evacuation of crankcase gases? I have used the manifold for the brake booster, which gives much better brake response and more constant vacuum, so I need to find a place for the PCV line. Currently, I’m venting under the truck, similar to the old “road draft tubes.”

I do have one line still connected from the passenger side valve cover to the CAI tube, so there is plenty of fresh air. I just want a better source of vacuum for the PCV valve, for the health of the engine.

Is this something that could be done safely?

pokismoki · September 22, 2022

i have elliminated the CAI vents feeding from the valve covers, one less place for oil injestion. get a set of uni valve cover breather filters and install em

Gandalf · September 22, 2022

Thanks, pokismoki. I do have one breather on the front of the passenger side valve cover, and I’ve eliminated both vents on the CAI tube. The driver side vent is capped, as I installed an oil cap one-way vent breather on that side. (https://www.c-f-m.com/performanceparts/pc/CFM-Performance-Billet-Valve-Cover-Breather-for-2014-15-Chevrolet-SS-Sedan-L3-6-2-p1803.htm).

My main concern is the gases escaping via the breather on the passenger side, and occasionally from the oil cap filter, which inevitably enter into the cab a bit. I’m probably worrying over nothing, as the crankcase with my setup cannot ever become over-pressurized - both the oil cap valve and the still existing PCV valve take care of evacuating gases. It’s confusing to me, I guess: one guy will tell you you need vacuum to pull the gases out of the crankcase; another says that the “positive pressure” pushes the gases out via the PCV just fine without a vacuum needed.

I am happy that I at least do not have any oil or gases being re-burned and coking up my valves. But, I would like to be sure that blow-by is being cleared completely out of the crankcase. One idea I read about that seems easy is to run the PCV line to the bottom of the air filter box, thereby utilizing a small amount of vacuum for pulling gases out of the cc, and allowing that small amount of gases to be filtered before re-entering the clean air intake and throttle body. Of course, a catch can would be used in line to trap the oil and water. Also, I think the longer hose length will help the oil to not roll all the way to the air filter box. Also, this would require a sealed air filter box (I have an S&B CAI, so it’ll work).

Lots of decisions! But luckily there’s also lots of room for experimenting. I’d love it to be as simple as using the vacuum pump for PCV, but I’m thinking that the vacuum pump must have an outlet for unused air, and it’s probably directed back into the engine, thus perhaps re-adding those gases back into the oil. I might just need to be happy with my current setup - at least it removes any chance of all those gases screwing up my valves.

pokismoki · September 22, 2022

the PCV in the manifold will clear any blowby out of the case. guys running catch cans on a daily N/A motor are a bit of an overkill. no need for a vaccum pump when you have manifold pressure. our trucks have vac pumps because we loose manifold press. when the engine switches to v4. otherwise you loose brake booster

Anyways, my other motivational purpose to blocking the cai valve cover vent ports, besides oil intake, was to stop unmeasured air from leaking past the MAF sensor by drawing air thru the valve cover vents. this tightens up the idle in various climates..

also you can remove the fuel tank vent line from the engine manifold. this is more for guys who want to hold a tight AFR, but requires a tuner to delete the CEL for the fuel tank emmisions code

Edited September 23, 2022 by pokismoki

Gandalf · September 23, 2022

That’s good to hear about the effect of blocking the two CAI ports. I did it with some cheap rubber caps. The air will also be cooler, especially if the CAI is a completely closed box with only the one fender inlet open.

Like most of us owners of the first generation of the LT engines (2014-2018), and possibly the second generation as well (2019-), I’m impressed with the horsepower and efficiency, but really don’t like the almost built-in age limit of the engines, due to the GDI system. I can’t see getting much more than 200,000 on the trucks without pretty major carbon cleanup. Thanks for sharing your experience.