After sending in a data log to my tuner, he informed me that the boost seemed a little low. He asked me to check the preload on the wastegate actuator, so I did, and it was set to the correct setting. So, the next thing was to search for boost leaks.
The tuner I use is Brian of Vermont Tuning. One of the things I really like about him is he owns and tunes his own Cruze, so he has a wealth of knowledge about these cars. One of the things he told me to check was the PCV valve located in the intake manifold. I was to pull the corrugated hose off the top of the manifold and look down inside to see if I could see a little orange nipple. I did, and guess what? There was no orange nipple.
The PCV gases flow up from the crankcase, pass through the cylinder head, and then route through the cam cover back down through a port in the head, where they enter a chamber in the intake manifold. The little orange nipple I was looking for is located inside that chamber. The orange nipple is how a small, circular, rubber flapper valve attaches the wall that separates that PCV chamber from the main channel of the intake manifold.
The circular rubber valve has the nipple in the center. From the intake side of the wall, the nipple pushes through a hole, and the valve covers a bunch of tiny holes surrounding the center hole. It works when the throttle is closed or the turbo isn’t providing a boost, and the downstroke of the pistons creates a vacuum inside the manifold. The vacuum pulls the circular valve away from the tiny holes and draws the PCV gasses into the main intake channel. From here, the gases can be recycled in the combustion chamber.
When the turbo is providing boost, the boost pressure inside the intake manifold pushes the rubber valve against the tiny holes closing that path. When that valve is closed, the gases are routed out of the chamber via the corrugated hose and through a one-way check valve attached to the turbo inlet. The air being pulled in by the turbo helps draw the gases through the valve and into the turbo. From here, they are pushed through the charge piping and back to the intake manifold to be recycled in the combustion chamber.
That is a brief description of how the system works, but there is a design flaw in the system. The flaw is the flaw of the rubber flapper valve with the little orange nipple. After some time, the little rubber valve gets sucked out of the hole it’s mounted in and ingested by the engine. The system works fine when not under boost, because the gases are drawn through the holes as intended. When the turbo is providing boost, the valve is no longer there to close off the holes, so now you have boost leaking into the PCV chamber. This will cause several issues, and the system will not work as intended. Unfortunately, this is a non-serviceable part, which means the intake manifold has to be replaced to fix the issue. You replace the intake manifold, then after some time, the entire process repeats itself.
Not wanting to replace my intake manifold every time the valve fails, I started searching for alternatives. I searched for aftermarket intake manifolds and came across Racer X Fabrication. The manifold they offer for the Sonic/Cruze doesn’t have an internal PCV valve. Instead, they offer a PCV kit with an external valve, fittings, and hose that will adapt and work as the factory system does.
After seeing the kit they offered, I started thinking it would be possible to adapt something similar to my OEM intake manifold. There is already an outlet from the PCV chamber that the corrugated hose attaches to, so what I needed to do was seal the holes on the inside and add a tee to that port. Sealing the holes wasn’t very difficult. A screw with a nylon and neoprene washer, along with some black gasket maker, did the trick. The more difficult task was the tee fitting.
I searched extensively for a tee fitting that would connect directly to the port but wasn’t able to find one anywhere. The wall thickness of the port the corrugated hose attached to was reasonably thick, so after measuring it, I determined I would be able to cut the tip off, then drill and tap it to a 3/8 NPT thread. Once that was completed, I threaded a 45-degree 3/8 NPT to -10AN fitting. This allowed me to add a -10AN tee fitting so I could start to build out the system.
The Racer X kit used a Bonomi check valve, which I purchased initially. Later, I stumbled across a valve by UPR Products that I wanted to compare with the Bonomi valve. The Bonomi valve has a 0.5 psi cracking pressure, compared to the 0 psi cracking pressure of the UPR valve. I liked that better, and I also liked that the UPR valve could be taken apart, cleaned, and inspected very easily, so I decided on the 3/8″ UPR check valve.
Using the Racer X kit as a model, I needed to adapt the valve to the intake manifold. The ZZP throttle body spacer was the perfect solution. Off of the tee, I initially reduced the -10AN to -6AN, then installed a 45-degree 1/8 NPT to -6AN fitting into the throttle body spacer. I installed the valve using -6AN push-lock hose clamped to either side of the valve, then used -6AN push-lock hose ends to connect the hose to the tee and fitting in the spacer.
Later, I replaced the -10AN to -6AN reducer with a -10AN to 3/8 barb fitting. This allowed me to move the valve closer to the tee and lengthen the hose from the valve to the spacer, which made the angle and connection a little better.
On the other side of the tee, I used -10AN hose and hose ends to run to the turbo inlet. I cut the corrugated hose off of the OEM check valve and pushed the -10AN hose onto it. Then, I used a Gates shrink clamp to clamp the hose onto the fitting and give it a nice, clean look.
So, with the holes inside the manifold sealed off, the gases will now be drawn up through the port with the tee fitting. When the intake is under vacuum, the gases will be pulled through the UPR check valve and into the manifold via the fitting in the ZZP throttle body spacer. When the turbo is providing boost, the pressure will close the UPR valve, and the gases will be drawn through the -10AN hose attached to the turbo inlet, the same as the OEM system does.
That is my PCV hack. I hope it works!
DS
