I had a '65 C20 V8 AT that I bought when it was only six months old. After a couple years of driving I figured the truck was due for a tuneup, took it to the local dealer. Within a short period of getting the truck back it started to stumble on acceleration. I took the truck back to the dealer, they had it for a couple of days, called and told me there was noting wrong with the truck. On my way home I noted that the truck was still pausing and/or stumbling on acceleration, back to the dealer. Was again told there was noting wrong with the truck.
I went home got out my factory manuals that I had bought when I bought the truck.
Reading through the tune-up section I noted a section about the PCV and how it should be serviced during a tune-up, IE, cleaning the valve in solvent and checking the valve for operation. I serviced the valve and reinstalled it, the truck ran fine.
The purpose of the PCV is to provide vacuum through the engine to draw out the blow-by, introducing same to the combustion chamber.
Upon acceleration the valve with-in the PCV snaps closed switching open to closed and thereby providing vacuum for the vacuum advance.
I went back to the Chevy dealer to explain the problem to them, the service writer did not understand the issue and the importance of servicing the PCV.. Hmmmmm factory trained tech's ? Wm.
