[eric32]

Hello guys I am making a new post here and some who have followed my other posts have known I am having carb related issues of things not wanting to work right like they should and also a bad studdering when letting off the throttle below 2000 rpm and things running very lean at times and adjusting my carb is not getting rid of things and erratic idle and off idle issues etc.

Ok on the video below the guy goes into details on checking for internal vacuum leaks. I left my pcv valve hooked up at first and took out my valve cover breather on the other side which is external and pictured below and took out the grommet to it and put in one of 3/4 ID size so I can hook up my vacuum gauge and see what is going on. I am getting conflicted things here.

In the video the guy plugs off the pcv valve or unhooks it and plugs it off and then hooks up his vacuum gauge on the port on the valve cover. He gets a vacuum reading and he states you should have pressure and not vacuum.

I am assuming he has the breather aka filter port plugged and then puts his vacuum gauge into the one valve cover port and he gets vacuum reading. I did the same exact way he did. I plugged off my pcv valve side and after doing that on the driver side it will slowly build up pressure. If doing the opposite it does the same thing. Plug off the driver side and hook up vacuum gauge to the passenger valve cover port it slowly builds up pressure.

Now if I hook up my pcv valve then the driver side where crankcase vapors should be coming out is then having a big vacuum sucking up through the breather port and if putting in my vacuum gauge it will go over ten plus inches of vacuum.

I know that last part is not the part of the test but is there anything going on here that is wrong? I have never had to check for an internal vacuum leak before but am just trying to throw all things out. With my pcv valve hooked up and it creating the huge vacuum on the other side to be pulled after its hooked up would indicate to me something is wrong as if I understand correctly even with the pcv valve hooked up the passenger side breather should be expelling crankcase vapors and it should be flowing to atmosphere and not sucking in, or am I wrong?

In the past with my pcv valve hooked up and stuff from memory I always had an open air filter on the driver side and previous one had an attachment to hook up a hose to your air filter element and I could swear I saw vapors blowing out of it if I remember correctly. I might be wrong.

But with out pcv valve hooked up and one side blocked it slowly creates pressure on the valve cover port regardless of plugging one side and putting vacuum gauge on the other and when the pcv valve is hooked up to the carb like normal it then creates a vacuum pulling in on the other side and will do it either way just like checking for internal vacuum leak.

Now how the pcv valve system works is should the one side be used for sucking in crankcase vapors and the other side should be expelling blow by vapors and it breath to the atmosphere as I have seen in the past or am I wrong there? Sorry guys for the post but hope you can help me out here. With the one port plugged and the other left open the engine will start up way better and does not shake and rattle and roll as bad and is smoother.

Once you hook up the pcv valve the engine shakes and studders really bad but beyond that I have to have the throttle way open past the transfer slot just to keep it running enough and thus my mixture screws don't adjust too well and is running rich for time being. Have not messed with anything else until I have confirmation that I have an internal vacuum leak going on.

Just trying to trouble shoot and eliminate potential problems and find the source of my issues.

Thanks guys and appreciate it.

 

[123pugsy]

PCV sucks in the blow by. There is not enough blow by to satisfy the PCV so the other side lets air in to the engine, not out.

 

[eric32]

So I take it 123pugsy that I don't have an internal vacuum leak and things are working normal as is? Sorry if I am out of the loop here. This is a first time doing this type of testing and digging into something like this.

 

[Phillip Nickles]

Eric32, paragraph 4 description makes me believe that you do not have engine vacuum into the crankcase of the engine. Breather vent plugged and pcv removed should cause a positive pressure in the crankcase due to the pumping action of the bottom of the pistons.
Your comment of the engine running better with the pcv hose blocked leads me to believe you may still an external vacuum leak ( carb to intake gasket, power brake booster if equipped, a vacuum hose, etc). Could also be a carb problem. I don’t know what has been tried up to this point.
i found it interesting in the video with intake removed the gaskets that failed were not steel reinforced whereas the felpro gaskets were reinforced. Since the heads did not have the usual bolt holes close the heat crossover it’s no wonder the first intake gaskets failed.
In the auto repair business we could pressurize the intake system with a machine that produced smoke to track down external vacuum leaks. This was absolutely necessary with systems that would not tolerate minor leaks which could result in lean fault codes.

 

[eric32]

Mr Phillip I have checked hoses and things so far and not coming up with any signs of external leaks. I checked the intake with it running and sprayed brake clean around the intake ports and stuff and it bubbles a hair and dries up but the idle does not change while doing so. It was hot and I am assuming the intake and heads being so hot too the touch that is why. I have replaced all the vacuum lines with proper size hoses and checked the brake booster and all the tests show its fine and sealing and holding vacuum and works as it should.

I have never caught or had an exernal vacuum leak by intake before so I don't know if something could be there external and spraying brake or carb cleaner is not enough to make a change to idle or not. I have another post on some issues I have came across and have tried to trouble shoot possible carb related but feel something else is going on somewhere as normal carb adjustments and changes is not happening after a certain point to the idle circuit in normal conditions.

An issue from previous motor is happening on this motor. Only thing carried over is the cylinder heads and distributor. Ignition is going good as usual.

 

[eric32]

Ok been watching some videos and stuff on how pcv systems work and stuff and I might be wrong as they are talking about how modern emission systems are hooked up and stuff unlike mine and other hotrodders. So if I am correct the pcv system when hooked up and it functions correctly and no internal leaks are there for the intake runners to suck in air from the lifter valley then with pcv valve hooked up and normal it will suck in air from one valve cover with the external air filter and will then from combustion gases and stuff will look for a way out and it will come out towards the pcv valve area and is being sucked in by vacuum of course from the carb or intake however one has it hooked up to one port or the other.

Am I correct? Just need clarification and I then can know I don't have an internal leak going on and its something else going on elsewhere.

 

[123pugsy]

See my post for a less round about way of what I think you're trying to say.

 

[123pugsy]

For trouble shooting your vac leaks, disconnect PCV and plug hose. Disconnect booster and plug hose. Disconnect all except the dizzy and plug hoses. How's it run with all disconnected and corked up?
Just keep in mind bolt threads cannot plug a vac hose. Air just corkscrews around the bolt threads.

 

[eric32]

123pugsy,forgive me if I sound wrong, what I am saying is basically on one thing and nothing else, is it normal when the pcv valve is hooked up in normal operation condition and the pcv valve is sucking up vapors into the intake through the carb while in park, the other side at the same time is sucking in air through the breather into the engine? If that is normal then I would guess I have no internal vacuum leak if I understand the way one shows up.

Have never checked for one before never saw what one side of the engine does with pcv valve hooked and what the breather was doing at the same time and never have experienced an external vacuum leak before except from a bad brake booster many years ago but I know the symptoms of one of those and went through the checks on that already and its fine.

Now on to other things, with the pcv valve disconnected and brake booster disconnected there is a difference but just slightly. The pcv valve when hooked up does lean out the idle some thus is leaning it out but nothing night and day difference.

When running without pcv valve the engine is more stable but the issues I am having are still there. Did not have time to take out and drive with everything disconnected minus vacuum advance and see how it would run but in park hardly any difference except with pcv valve and it adding extra air like normal. Had to have a too high of a setting to get engine to stay running and hard to start. Very shaky and erratic.

I have explained some things in another post and did not want to add anymore to it and cause me to not get any help with checking other things. Something is causing I believe carb related issues and am trying to find out a problem that has plagued me from previous build into this one. Have two issues going on I can't figure out and am trying to rule out all chances of vacuum leak somewhere.

 

[123pugsy]

123pugsy,forgive me if I sound wrong, what I am saying is basically on one thing and nothing else, is it normal when the pcv valve is hooked up in normal operation condition and the pcv valve is sucking up vapors into the intake through the carb while in park, the other side at the same time is sucking in air through the breather into the engine? If that is normal then I would guess I have no internal vacuum leak if I understand the way one shows up.

Think about it logically and not just what you read. The air that is being sucked out must be replaced. If not, your engine would suck itself inside out like an oil tanker rail car. So logic says the air will be sucked in thru the filter on the other side. There is no where else unless it sucks a gasket right out and brings air in that way. Blow by pressure only replaces some of what is being sucked out.
When you see oil coming out of a breather, it's usually after giving it the mustard on the go pedal and there is more blow by pressure than is being sucked thru the PCV system. Air pressure must go somewhere.

I have no idea how the PCV in operation can tell you that you have no internal vacuum leak.
It must be disconnected at the carb and plugged in order to do the test. The PCV has no bearing on your test.

Vacuum without any air getting in:

 

[eric32]

I don't know what else to honestly to say on the one thing. My apologies I don't know all the science about things here. I gave all the information on what I did in plain detail. I checked with the pcv unhooked from the carb and the valve cover where it goes plugged so nothing can go in or out.

I then took out my breather on the other side and as the engine was running I put my vacuum gauge over the hole plugging it with my gauge too see if any vacuum was being pulled and it showed no signs of that and the vacuum gauge slowly would build up pressure and once I pulled out my gauge I got a big woosh of air blowing out.

That was how I have seen done to test for internal vacuum leaks. Plug the one side,unhook the pcv valve from carb and plug the carb, then ran engine and took out the breather and while it was running put the vacuum gauge on the breather hole and see if any vacuum is being sucked in.

From my understanding if you get pressure when the other side is plugged then your good, but if you get vacuum pulled in with the other side plugged then you have an internal vacuum leak and most likely the intake is at fault pulling vacuum from the lifter valley area.

I only tested again to see what happened when my pcv valve was hooked up and I know that won't tell you if you have an internal vacuum leak and was just curious on that part and nothing else and when I saw that I had vacuum being pulled in that was what caught me off guard after all these years I thought one side was always pulling in and the other side was blowing out.

Just from one time in the past on a breather I saw vapors blowing out or I should say slightly flowing out at idle but never actually put my finger or a paper up to breather to see if it sucked in any air. That why I asked is it normal for the breather side to suck in vacuum while the pcv valve is hooked up. I just did not know if that was the normal way it would be and I guess coming to how I worded things I can see how I might have confused folks. My apologies there. I just wanted to make sure I was not missing something and reading something wrong as my limited experience on this one thing and testing for the first time caught me off guard.

I am not an expert on the function of the engine such as crankcase vapors and the effects of air being pumped in and the effects and other stuff. I kind of have an idea but have never really dealt into all that as I never had too. I understand the engine is like a vacuum pump and sucks in air to make power and works with all the other things and air is compressed in the cylinders and then let out the exhaust after combustion.

Appreciate your time and help and its much appreciated.

 

[1979Malibu]

Anytime I've seen an internal vacuum leak at the SBC intake, the corresponding spark plug or plugs showed signs of oil consumption in the cylinder or cylinders pulling the vacuum in from the lifter valley. A vacuum leak there is almost certainly going to pull in some oil.

 

[eric32]

Yeah plugs have all been dry and clean, just something going on and trying to diagnose things. Appreciate your time.