[SD421]

FWIW, the biggest improvement that was made was to change the stock PCV Valve to one that doesnt "leak" as much. With 12" of vacuum, the stock PCV Valve creates too much of a controlled vacuum leak.
Changing it steadied the idle and I also noticed no more gas smell because its staying longer in the crankcase to get burnt up. The part # is in the pic below.
My signature explains my setup.
-Don

[Dick Boneske]

The CV881C PCV valve is available on Amazon for $4.98 with free shipping if you have a Prime account.

You've said this valve "leaks" less air than the stock one. Do you know the stock recommended application for this valve and how much less flow it allows than the stock one?

[SD421]

Originally Posted by Dick Boneske

The CV881C PCV valve is available on Amazon for $4.98 with free shipping if you have a Prime account.

You've said this valve "leaks" less air than the stock one. Do you know the stock recommended application for this valve and how much less flow it allows than the stock one?

Dick,
The stock application for this valve according to my research is a 1985-1993 GM car. I dont have any other info.

That was how the shop guy explained it to me as a controlled vacuum leak. The lower vacuum amount requires a different pcv valve.

[SD421]

Looking back at my first post and thinking of what the PCV Valve actually does, I need to change what I said.
This new PCV Valve slows down the amount of crankcase vapors leaving from the Valley Pan and entering the intake manifold thus the idle is steadier plus it required the center carb to be readjusted to be leaner. The shop was using a tailpipe sniffer and was adjusting based on the A/F Ratio.
Center carb was originally adjusted richer to make up for the original pcv valve which again was creating a bigger controlled vacuum leak.
This accounts for the lack of the smell of gas at idle and a very steady idle with a cam that has 12" of vacuum.
Don

[Singleton]

There's some of these pcv's on ebay for 3.99/free shipping

[Tom Vaught]

Originally Posted by SD421

Looking back at my first post and thinking of what the PCV Valve actually does, I need to change what I said.
This new PCV Valve slows down the amount of crankcase vapors leaving from the Valley Pan and entering the intake manifold thus the idle is steadier plus it required the center carb to be readjusted to be leaner. The shop was using a tailpipe sniffer and was adjusting based on the A/F Ratio.
Center carb was originally adjusted richer to make up for the original pcv valve which again was creating a bigger controlled vacuum leak.
This accounts for the lack of the smell of gas at idle and a very steady idle with a cam that has 12" of vacuum.
Don

What you have posted makes sense.

1) The PCV Valve has a calibrated orifice inside it and a spring designed to allow a given amount of flow during some modes, restrict the flow to the engine under other modes like decel vacuum spikes, and close in case of a intake backfire so that flame would not enter the Valley pan/ oil pan area.

So your 12" vacuum reading was not allowing the valve to work properly in its control range.

2) Some people remove the PCV valve then have lots of gas smell thru the open breathers, as the nasty crankcase gases have to go somewhere. In your case you reduced the amount of flow from the crankcase, reset the air/fuel ratio, and you and the engine were happy. With a lower vacuum camshaft reading that means that you also have more EGR dilution therefore less "good air" so the Air/fuel needed to be reset too.

3) It makes sense that a later model GM PCV valve would work better, as the later model cars also used more EGR in their calibrations (similar to your additional EGR effect from the rumpier camshaft).

Maybe others can benefit from your post.

Tom V.

[SD421]

Originally Posted by Tom Vaught

What you have posted makes sense.

1) The PCV Valve has a calibrated orifice inside it and a spring designed to allow a given amount of flow during some modes, restrict the flow to the engine under other modes like decel vacuum spikes, and close in case of a intake backfire so that flame would not enter the Valley pan/ oil pan area.

So your 12" vacuum reading was not allowing the valve to work properly in its control range.

2) Some people remove the PCV valve then have lots of gas smell thru the open breathers, as the nasty crankcase gases have to go somewhere. In your case you reduced the amount of flow from the crankcase, reset the air/fuel ratio, and you and the engine were happy. With a lower vacuum camshaft reading that means that you also have more EGR dilution therefore less "good air" so the Air/fuel needed to be reset too.

3) It makes sense that a later model GM PCV valve would work better, as the later model cars also used more EGR in their calibrations (similar to your additional EGR effect from the rumpier camshaft).

Maybe others can benefit from your post.

Tom V.

Thanks Tom that means alot to me. I remembered about the posts where guys are having the issue of too rich a mixture with their combo, this fix might be their "fix" too.
Don

[Tom Vaught]

AGREE! Good job on that diagnostic and getting the engine happy again.

Tom V.

[SD421]

Originally Posted by Singleton

There's some of these pcv's on ebay for 3.99/free shipping

Just clicked on your video and I remembered seeing before BUT I didnt know it was your Goat. Sounds real nice.
Don