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Looking over my buddies Chevy Cruze because he took it to the dealership and they saw lean codes and wanted to start throwing fuel system parts at it.
Freeze frame indicates the code set at Idle. I pulled up LTFT, STFT, upstream and downstream O2 sensors. At idle LTFT & STFT were both at 35%. Snap the throttle and the upstream O2 pegs rich ruling out fuel pressure and MAF right? Increase rpm and fuel trims start to drop. Indicating a vacuum leak.
It seems the PCV valve is built into the valve cover on this model. I have heard of these having issues. When I plug the hole on the PCV valve the fuel trims start to correct, but they’re still high. My question is.....do I pull the trigger on the valve cover and keep troubleshooting after that? Or are is there something else I’m over looking. What’s the call here?
"Knowledge is a weapon. Arm yourself, well, before going to do battle."
"Understanding a question is half an answer." I have learned more by being wrong, than I have by being right.
Tyler saved my bacon on one those a while back. The cause of the PCV diaphragm failure is the lack of a little rubber metering device in the intake manifold.
There's a 3/8ths diameter port between the #2 and #3 intake runners. If you pop the hose off and look straight down the hole, you should be able to see the tip of a little orange rubber cone poking horizontally into the chamber from the engine side toward the firewall.
If the cone is gone, she'll keep eating valve covers.... Stupid IMO.
VC was around $100
Intake $500ish, loaded. Fuel rail, injectors, TB, etc...
Noah called it. The failure of the Non-Return Valve in the intake causes the failure of the valve cover. If left that way for too long, it can also cause piston ring land damage. The newest version of this GM PIP includes pictures of what to look for:
I don’t know why I haven’t been getting notifications for this post but I just read all of your responses. Thanks for all the information. I’ll definitely check out that PIP and do my research. I did hear somewhere that the valve cover is the effect and not the root cause. I don’t quite understand what the valve is in the intake, how it works, or what the effect is on the valve cover. But I will read up on it and educate myself. Unfortunately I think the car has been running this way for a while now. I pulled the oil cap and there is a LOT of blow by, seems as if the ring lands are already damaged. Is it worth the trouble of putting new intake or valve cover on it (after troubleshooting it more of course)? Or has the damage already been done. The car only has 100k on it.
Does you guys have any solid material I can read up on too understand this system better? Why is it that it destroys the pistons? Engine runs too lean and burns up the ring lands? Thanks again for all the help and support.
I'm no engineer, but I cal tell you what I've seen from experience.
It's my understanding that the non return valve is there to allow normal PCV system operation off boost, but block boost pressure from going into the crankcase when boosting. That's important so you don't blow out seals and such. :lol:
When the non return valve breaks, it allows full manifold vacuum and boost pressure into the crankcase. That causes the sensitive diaphragm in the valve cover to pop, and also explains why you found vacuum at that port in the valve cover.
Again, not an engineer, but I've been told that a result of the extreme pressures in the crankcase causes the pistons to 'flutter' and break ring lands. Did I mention I'm not an engineer? :silly: Just what I've been told.
That makes sense, I was wondering with it having a turbo if that valve had anything to do with boost pressure. I read over that PIP. I think I'll check the intake for that valve and then maybe do a compression test before replacing any parts.
The failure of the Non-Return Valve in the intake causes the failure of the valve cover. If left that way for too long, it can also cause piston ring land damage. The newest version of this GM PIP includes pictures of what to look for: