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There is not much to a PCV.
With the engine running pull it out of the valve cover and feel for suction.
It would be better if you just stated what the problem is.
I just replaced mine. Engine was blowing fumes out at idle from opposite side valve cover breather instead of pulling fresh air in. I tried several before I found one that worked correctly with my engines vacuum numbers.
Fram FV181 worked for me with a idle vacuum around 10-11
Last edited by Bloodzone; Sep 1, 2020 at 04:21 PM.
There is not much to a PCV.
With the engine running pull it out of the valve cover and feel for suction.
It would be better if you just stated what the problem is.
OK here is the issue, the car starts and idles just fine. When you put it in drive and go it "sputters" like there isn't a constant fuel supply. When you get going it runs and reaches high speed but you can feel the car "sputter". My brother in law (who is a gear head) went for a ride with me and he could feel the slight sputter. We looked at the fuel injectors and they appear to be functioning correctly. He did make the comment that he thought there was to much gas but then backed tracked on that statement. His opinion is that it is a vacuum issue and suggested replacing the PCV valve as a easy cheap starting point.
A PCV Valve can fail in 2 ways. One , stick open. Total loss of vacuum. 2 stick closed. As mentioned above. The old service manuals tell you to remove it and shake it. Do you hear it rattle? If not replace it.
yes they come in different vacuum pull off ratings. Hard to decipher. However, your engine sounds fairly stock. A standard replacement would be cheap enough.
I would check it for rattle and vacuum as mentioned above. But I seriously doubt this is your stumble . What is your fuel pressure???
I was gonna make another post about this but found your post, not trying to take over but just had a question. I just got my 78 with 400 small block. Is this the PCV valve and if so do they usually seep a little? It is hard to see but there is a little liquid on in the grooves of the cover.
If the PCV valve does not completely close at idle, it will leak vacuum and idle speed and idle quality can suffer greatly. If it is closed ALL of the time, you can get oil misting in engine compartment. Just because it rattles does not mean the PCV valve is sealing adequately. You need to lightly blow thru the 'bottom' port to see if it blocks airflow with light pressure; then blow harder to make sure it opens. I know....YUCK! Get over it...you have to test this stuff..........
I was gonna make another post about this but found your post, not trying to take over but just had a question. I just got my 78 with 400 small block. Is this the PCV valve and if so do they usually seep a little? It is hard to see but there is a little liquid on in the grooves of the cover.
there is no PCV in your picture.
start a new thread
Its my understanding that a PCV valve should not block 100% air flow at any point during normal operation. Even at idle you still need engine ventilation and if the PCV is blocked then it will be forced out other areas.
It should be tuned to the engine's vacuum to allow the correct amount of ventilation all the time under all driving conditions. I could be wrong this is what makes sense to me.
From: Arizona - If you don’t know CFI, STOP proliferating the myths around it...
Originally Posted by rmichael63
OK here is the issue, the car starts and idles just fine. When you put it in drive and go it "sputters" like there isn't a constant fuel supply. When you get going it runs and reaches high speed but you can feel the car "sputter". My brother in law (who is a gear head) went for a ride with me and he could feel the slight sputter. We looked at the fuel injectors and they appear to be functioning correctly. He did make the comment that he thought there was to much gas but then backed tracked on that statement. His opinion is that it is a vacuum issue and suggested replacing the PCV valve as a easy cheap starting point.
Thoughts?
OK, this sounds like the classic CFI issue with fuel pressure. These motors are very fuel pressure sensitive. First off, do you have a GM service manual? If not, get one. It has everything in there to troubleshoot and maintane your 82 CF. Second, do you know what your fuel pressure is set to right now? If not, you need to see what it is and set it to 13psi. FP is checked in-between the TBs only. Then run your car and see if it doesn't run much better. GM spec is range for FP is 9-13psi. I can ASSURE you 100% if you run your FP at 9psi it will run like crap and setting it to 13psi will seem like you installed a different motor in there.
Last edited by Buccaneer; Sep 2, 2020 at 12:20 PM.
A PCV Valve can fail in 2 ways. One , stick open. Total loss of vacuum. 2 stick closed. As mentioned above. The old service manuals tell you to remove it and shake it. Do you hear it rattle? If not replace it.
yes they come in different vacuum pull off ratings. Hard to decipher. However, your engine sounds fairly stock. A standard replacement would be cheap enough.
I would check it for rattle and vacuum as mentioned above. But I seriously doubt this is your stumble . What is your fuel pressure???
We were looking for the schrader valve (sp) but couldn't see one on top after taking the air filters off ... it appears i need to get that checked ...
The PCV valve IS supposed to completely block airflow at idle conditions. Find me ANY piece of literature [written by real car folks) that states otherwise. The only way for it to NOT negatively affect idle conditions & quality is for it to be sealed (pintle to seat, metal-to-metal). The valve cannot be opened at all at idle for the PCV valve to work as intended. Might there be a little leakage at that pintle/seat interface? Yes, but the valve must be seated so that the amount of airflow getting by the pintle is exactly the same every time when the engine is at idle. Then you can still properly adjust air/fuel mix with the idle adjustment screws.
From: Arizona - If you don’t know CFI, STOP proliferating the myths around it...
Just a heads up for all the responses here from members that do not know about CFI fuel pressure checking. CFI IS different than any other fuel injected motor that GM made and it IS a TBI system with two injectors. They do not have a schrader valve for the FP gauge to plug into. To check the fuel pressure properly, there are two ways, but one way you have to actually modify the throttle body and if you screw it up, you just trashed the TB. The other way which is the most common way is to measure the fuel pressure in-between the TBs at the crossover tube. You will not get an accurate read if you go down stream from the TB and check it at the fuel filter. To check pressure in-between the TBs you can either modify the crossover tube and install a gauge (generally doing this will trash the 45* flare nuts and it will leak) or see what I have to help you out. The choice is yours... Remember, the most correct setting for CF is 13psi, anything less and your performance will suffer.
Last edited by Buccaneer; Sep 3, 2020 at 11:36 AM.
You may have a vacuum leak, or not. You can have a vacuum leak due to a bad PCV or from a variety of other spots. PCV valves are cheap & easy to replace and IIRC service manuals recommend periodic replacement. In general I don't espouse parts replacement as a diagnostic tool; but a simple exception here. Replace PCV as matter of routine maintenance; and it just may help your issues as well.
No problems with me. Everyone has a right to their opinion.
But, why would that valve have a spring in it if it was supposed to be open all the time?
Excerpt from "Crankcase Ventilation System" Wikipedia
"The PCV valve controls the flow of crankcase gases entering the intake system. At idle, the manifold vacuum is high, which would draw in a large quantity of crankcase gases, causing the engine to run too lean. The PCV valve closes when the manifold vacuum is high, restricting the quantity of crankcase gases entering the intake system.[9]
When the engine is under load or operating at higher RPM, a higher quantity of blow-by gases are produced. The intake manifold vacuum is lower in these conditions, which causes the PCV valve to open and the crankcase gases flow to the intake system.[10] The greater flow rate of intake air during these conditions means that a greater quantity of blow-by gases can be added to the intake system without compromising the operation of the engine. The opening of the PCV valve during these conditions also compensates for the intake system being less effective at drawing crankcase gases into the intake system in these conditions."
