Someone please school me on pcv valves

[Catfish28]

ok. So my 78 2f developed an issue over the past week. There is a relatively loud squealing coming from the engine and I checked all the usual suspects with belts and pulleys with no relief. Then I got a wild hair and pulled the pcv valve off the side of the crank case and it stopped. Tested the pcv valve and alls well. If I let the pcv valve vent to air and plug the line to the intake manifold then the squealing stops and truck idles better than ever and seems to have more power. Top of valve cover is vented to the air cleaner. Anybody got any ideas?

 

[Dizzy]

How did you test the PCV valve?

A PCV valve controls the amount of manifold vacuum which purges the crankcase of oil-sludging-fumes. It is a flame arrester in the event of intake backfire, so your crankcase doesn't combust. Air is drawn into the valve cover from the air cleaner, then to the crankcase. If it is clogged a bit, it might not make its partial seal. You might clean it with solvent, but they are cheap, so get a new one. A good fitting dipstick seal helps the PCV do its job.

 

[Catfish28]

Tested by just blowing thru it from the crank case side. And then from the manifold side. Blew unrestricted from the case and sealed from the other. I could understand if the valve cover wasn't vented correctly that the rear main may be causing the noise. But that isn't the case.

 

[Solace in Solitude]

Also, make sure the PCV is installed correctly... it’s a one-way valve.

 

[Catfish28]

Did that as well. Flows freely from the crank case side.

 

[Dizzy]

It should be partly restricted blowing from the crankcase side, there might be your whistle. And of course, totally closed pushing air from the manifold.

 

[Dizzy]

By design, if the PCV valve were totally open to draw air from the crankcase, then it would be like a vacuum leak on the intake, hence the poor idle. So that is why the PCV valve has to be able to move, to close in the event of intake backfire, and to open just the right amount for drawing blow-by gasses out of the crankcase without interfering with your air/fuel ratio, or air/fuel/EGR ratios.

 

[Catfish28]

All good stuff guys. Thanks. Looks like I'll be replacing the pcv valve just to be safe. Does an oem pcv valve have the "teq" logo or something else to distinguish from aftermarket?

 

[65swb45]

If an induced vacuum leak causes your truck to run better, then your carburetor is running too rich and the vacuum leak is helping achieve a better AF ratio.

Looks like you’ve got more homework than just a PCV.

 

[Catfish28]

I had the pcv valve attached when it was idling better so I wasn't causing a huge vacuum leak. So I probably still have an AF issue but not as bad as if I had caused a huge vacuum leak. Because with the pcv attached it's adding some air to the mixture at all times correct?

 

[MBest75]

Just last night had this same issue after a full blown desmog and Weber Carb install. Not too sure how, but after a test drive my PCV Valve hose was disconnected. I was fairly certain it was connected before firing the engine back up after the desmog/carb change out which took me a few weeks to complete while waiting on parts. I reconnected it and the engine basically died. When disconnected the hose to the manifold was pulling air. I could reconnect the PCV hose and disconnect a vacuum gauge hose that was hooked up and it ran fine. Awaiting arrival of a new PCV valve and grommet and then will restart my carb tuning process as I'm undoubtedly too rich if it runs better with a vacuum leak. Always something...

 

[Dizzy]

The PCV is drawing blow-by gasses, the PCV valve regulates the amount of it, yes at all times. It is kinda inert, because it is already mostly burnt.

Mark, I believe that Catfish said that he capped it when it was disconnected, so there would be no vacuum leak.

MBest75, where was the PCV disconnected, at the manifold, before the valve or where the valve connects to the motor?

 

[MBest75]

The hose that leads from the PCV valve around the air cleaner to the manifold was disconnected.

 

[Catfish28]

Yes. If you're running good with that vacuum leak you've got a carb problem.

 

[FJ40Jim]

View attachment 1731468 The hose that leads from the PCV valve around the air cleaner to the manifold was disconnected.

Replace the tin PCV valve with a new OEM billet steel valve from Toyota. It is expensive ($10 vs $2), but works right and last forever.

To the OP: when adding PCV to the crankcase makes the engine shriek/squeal/whistle, it is usually because the crankcase is building vacuum and the crank seal(s) are making a racket as they try to get sucked into the engine. look to a PCV valve that is out of calibration and/or a restriction in the valve cover baffle or side cover baffle.

 

[Catfish28]

Following up on this, I picked up and put on a new oem pcv valve and it's amazing how much better it's running. I couldn't get it to idle below 1000 or so rpms and was having a variety of other AF related issues. Replaced the cheap tin aftermarket valve with oem. Best $11 I've spent in some time.

 

[saltfever]

Just last night had this same issue after a full blown desmog and Weber Carb install. Not too sure how, but after a test drive my PCV Valve hose was disconnected. I was fairly certain it was connected before firing the engine back up after the desmog/carb change out which took me a few weeks to complete while waiting on parts. I reconnected it and the engine basically died. When disconnected the hose to the manifold was pulling air. I could reconnect the PCV hose and disconnect a vacuum gauge hose that was hooked up and it ran fine. Awaiting arrival of a new PCV valve and grommet and then will restart my carb tuning process as I'm undoubtedly too rich if it runs better with a vacuum leak. Always something...

MBest75, I have a desmogged 75 with a Weber carb. Not sure the PO desmogged correctly. I just replaced the rear main seal, oil pan gasket, timing cover gasket and seal due to oil leaks. Now to my surprise the front is leaking oil. I’m thinking it’s a combination of the desmog vacuum hoses not correctly connected and the pcv valve not working. Would you have any photos of your desmogged 75 you could share? Other thoughts / recommendations welcomed. Thanks!

 

[FJ40Jim]

The PCV hose should remain in place, from elbow fitting in side of intake, over top of engine to billet steel PCV valve at rear of pushrod cover.
The other half is to connect a hose from air cleaner to breather port on top rear of valve cover.

 

[saltfever]

Jim, thanks. That looks like what I have. I’ll check the hoses and replace the pcv valve.

 

[billmc]

Replace the tin PCV valve with a new OEM billet steel valve from Toyota. It is expensive ($10 vs $2), but works right and last forever.

To the OP: when adding PCV to the crankcase makes the engine shriek/squeal/whistle, it is usually because the crankcase is building vacuum and the crank seal(s) are making a racket as they try to get sucked into the engine. look to a PCV valve that is out of calibration and/or a restriction in the valve cover baffle or side cover baffle.

Hi Jim, do you have a part number for the steel PCV valve?