Can someone explain the function PCV
Thread Starter
Intermediate
Joined: Nov 2018
Posts: 25
Likes: 7
Can someone explain the function PCV
My C7, due to its year of manufacture, still has two of these "valves" that can be easily removed and tested, if you know how they're supposed to work 🤪.
The flow should be from the crankcase towards the intake. The valve "rattles," I cleaned it with brake cleaner, and there's almost no visible oil residue. In its installed position (valve opening angled downwards), the valve can be blown through from both sides. When I remove the valve and hold it with the opening facing upwards, the valve closes when blowing towards the crankcase, but that's not how the valves are installed. I bought both valves (in my case, they're the complete hoses with the valves) new, and it's exactly the same. As I understand it, the PCV valves cannot function as valves in their installed position. Could someone explain this to me?
The flow should be from the crankcase towards the intake. The valve "rattles," I cleaned it with brake cleaner, and there's almost no visible oil residue. In its installed position (valve opening angled downwards), the valve can be blown through from both sides. When I remove the valve and hold it with the opening facing upwards, the valve closes when blowing towards the crankcase, but that's not how the valves are installed. I bought both valves (in my case, they're the complete hoses with the valves) new, and it's exactly the same. As I understand it, the PCV valves cannot function as valves in their installed position. Could someone explain this to me?
Thread Starter
Intermediate
Joined: Nov 2018
Posts: 25
Likes: 7
Hallo Jack, danke für deine Antwort. Wie du beschrieben hast, sollte das Ventil genau gleich funktionieren; das war auch mein Verständnis. Leider hat das Ventil, genau wie die neuen, die ich bestellt habe, nach dem Einbau keinerlei Funktion, außer als Schlauch. Wenn man von der Ansaugseite in das ausgebaute Ventil suck, während die Ventilöffnung (motorseitig) nach oben zeigt, schließt es. Aber es ist in die falsche Richtung gerichtet und natürlich nicht so eingebaut. Wenn die Ventilöffnung nach unten zeigt, wie es im eingebauten Zustand der Fall ist, lässt sich die Ventilfunktion nicht reproduzieren. Neue Ventilschläuche rechts und links zeigen keinen Unterschied zu den zuvor eingebauten. Könnte es sich um einen Konstruktionsfehler von GM handeln, der später zu Änderungen an den Ventilen geführt hat?
Last edited by meikel24; May 14, 2026 at 07:22 AM.
Racer
Joined: Nov 2015
Posts: 260
Likes: 87
From: Brighton MI
As opposed to sending it into the atmosphere as done in the old day when we had Road Draft Tubes.
I have installed catch cans on all of our vehicles to reduce the amount of crankcase emissions that flow through the throttle body.
I have installed catch cans on all of our vehicles to reduce the amount of crankcase emissions that flow through the throttle body.
Melting Slicks
Joined: Feb 2018
Posts: 2,157
Likes: 1,032
From: North Texas
MHO:
All my 'good' cars run direct and port injection, ie: Toyota, Lexus for example..
All my 'junk' cars run direct injection only, ie: GM for one.
All Corvettes are direct injection except the ZR1 which is direct and port. This is the correct set up which all Corvettes should have. If Toyota can do it on a $30 - 35k car, GM should be able to do it on a $70k Corvette.
Port injection keeps the valves 'clean' by fuel washing over them. No need for catch cans or walnut blasting or any type of involved cleaning or fancy 'add ons' to keep the valves carbon free. The port injection gas, with all its additives, does it for you.
Just think, your paying for all these additives gas company's have developed over many years and on a direct injection only engine they do nothing to elimate the carbon build up that they were developed for. One step forward, two steps back.
Oh, just a side note: my Lexus also does not have AFM. Way to go GM, direct injection and AFM what could possibly go wrong?????
All my 'good' cars run direct and port injection, ie: Toyota, Lexus for example..
All my 'junk' cars run direct injection only, ie: GM for one.
All Corvettes are direct injection except the ZR1 which is direct and port. This is the correct set up which all Corvettes should have. If Toyota can do it on a $30 - 35k car, GM should be able to do it on a $70k Corvette.
Port injection keeps the valves 'clean' by fuel washing over them. No need for catch cans or walnut blasting or any type of involved cleaning or fancy 'add ons' to keep the valves carbon free. The port injection gas, with all its additives, does it for you.
Just think, your paying for all these additives gas company's have developed over many years and on a direct injection only engine they do nothing to elimate the carbon build up that they were developed for. One step forward, two steps back.
Oh, just a side note: my Lexus also does not have AFM. Way to go GM, direct injection and AFM what could possibly go wrong?????
Last edited by Tinkertech; May 16, 2026 at 08:28 AM.
