Do you have a fresh air inlet that connects to the engine that supplies the fresh air before the throttle blade? This probably isn't the problem since you mentioned you have the problem even with the PCV disconnected.

 

Do you have a fresh air inlet that connects to the engine that supplies the fresh air before the throttle blade? This probably isn't the problem since you mentioned you have the problem even with the PCV disconnected.

i do not have anything hooked before the throttle blade. I have a vac line running off back of intake to the oil fill tube but nothing before

 

On my 1989 Mustang, I had a vacuum source line going from the upper intake to the PCV valve. This pulls air from the crankcase.

I also had a fresh air inlet line connected from the engine air intake tube (after the MAF and before the throttle blade) that connected to the oil fill tube on the valve cover. This was for fresh air to enter the crankcase.

 

My pcv is hooked to back of intake. On my holley upper it has three ports on the back so i did one to the factory vacuum tree and one to oil fill and other to my fuel regulator? Crazy how many times i have redone these lower gaskets as soon as i fire it to set the timing it is sucking air like a shop vac. Even with all vac lines undone and i can put my hand over the pcv grommet and straight suction. Hope its not in my heads or lower end.

 

If you have a PCV valve pulling air out of the crankcase without a fresh air source hooked up to the engine then it will try pulling air into the crankcase from the valve cover gaskets, oil pan gasket, front & rear main seals, front & rear rear lower intake gaskets, etc.

 

If you have all the vacuum sources removed from the v-covers, etc then the only place a vacuum can get to the crankcase is through an intake port when the piston goes down.

There are two places this occurs: Between the head/intake or through the valve guides/valve seals.

1. Wrong intake gasket is being used..
2. Gasket is slipping out of position when tightening gasket.
3. Distance between the surface of the head and the intake is more than the gasket is thick..milled heads or intake or both can cause this..
4. Worn v-guides thus bad v-seals.

ks

 

So i have have redone these gaskets 6 times with the holley intake and i can see in the ports pretty well to align them as i set it down and torque it. Once i tried a set of cometic gaskets that are thicker because when i would remove the intake I noticed the china wall bead was paper thin. When i tried my gt40 intake set up i could not see down the runners but felt good about the gasket placement still no change though so i felt like i eliminated the intake being the problem. Everything is brand new except for lower end and heads but they only have 1200 miles. The engine did sit for 5ish years and when i went back in i did new head gaskets and studs. Hasnt been right since. Valve seals or guides maybe from sitting? Or am I really just missing something on this gasket install?

 

If you are trying to troubleshoot a vacuum to your crankcase then don't add anymore vacuum hoses. Unhook EVERYTHING to the intake. Every single tiny hose that either goes to the valve covers or to the lifter valley on the bottom of the intake, etc..

Once there is no vacuum source to the crankcase then start it up and see if there is a vacuum being pulled by removing the oil fill cover and put your hand over it. If there is still a strong vacuum then it has to be intake or valve guides.

With absolutely no vaccum source there should be a slight amount of pressure developing inside the crankcase that will puff out steam/smoke or ?? out of the oil fill hole.

ks

 

Ok. I have eliminated all vacuum over the summer with the holley on there. I will eliminate it all tomorrow and fire it again and check it. Good to hear there is no way its in the lower end it sounds like. Can’t believe this thing has beaten me like this.

 

You mentioned that you felt like the intake gasket was aligned but it's possible that if the heads were angled milled or something weird then the surface angles between the intake and head are not parallel causing the gasket not to sit flat thus not sealing.
I always use a thin film of silicone around all intake and water ports to help with any mis-match but not sure if you have done this.
Also, I never use front/rear intake manifold gaskets, instead I just use about a 3/8' tall bead of silicone to seal the end rails of the intake to the block. This guarantees that the intake doesn't sit too high on those end rail gaskets causing leaks around the intake ports.

ks

 

A broken bottom end (rings/piston, head gasket, etc) usually produces pressure and blows smoke out the breathers like a choochoo train.
It's definitely topend just need to isolate areas...

ks

 

Awesome! Guess i need to really concentrate on this upper area and find it. I will start by unhooking all vac lines and then do another leak down test to make sure valve seals and guides are good? Maybe blow smoke through the dipstick?

 

The vac line to your oil fill neck is your problem. That’s wrong. You’re pulling a vac on the crankcase doing that.

 

You need a PCV valve on one valve cover and a VENT on the other valve cover to allow your PCV to work correctly..
I am guessing your PCV is drawing a vacuum with NO source of air INTO the engine... I have seen this before..

 

Mostly correct. As written, that’s the typical arrangement for a mod motor. Locations don’t have to be on valve covers. A typical pushrod engine will have the PCV valve in the back of the intake manifold where it draws from the valley under the intake and the fresh air line to a valve cover (oil fill neck).

To generalize, a correct PCV system will have a PCV valve placed with access into the crankcase and have a hose running from it to a vacuum source. The fresh air tube will connect between a different crankcase location and a metered air source pre throttlebody (assuming MAF) that won’t see pressure if forced induction.

 

I noticed that the engine sat for years. Could it have gotten cold, froze and cracked a head from having water in it?

ks

 

It did sit for some years…in and out of the car. I really feel like i am doing the gaskets well and heads only have 1200ish miles so i would think the cracked head could be a real possibility. It passed a leak down and compression test but it still could have a crack i guess? Is there a way to test or they would have to come off and go to a machine shop? I also appreciate all your input by the way!

 

There is a thread floating around this sight about doing a smoke test to find leaks. I think it was more for testing turbocharger piping but this would also be a great way to find any vacuum leaks around the intake ports once you get that far.

ks

 

Flow of the PCV system-
The PCV cycles Fresh metered air through the crankcase and into the intake, pulling blowby with it.

that fresh air enters at the passenger valve cover. You have removed that source of fresh air and instead supplied a vacuum source there, so that no air ever enters the crankcase.

that is your only problem.
not the gaskets, not the valves, rings, heads, intake or bottom end.
it is the missing supply of fresh metered air.

Metered air ENTERS the crankcase at the passenger valve cover, is then pulled throughout the crankcase, up through the PCV valve and back into the upper intake plenum (the vacuum source).

Do Not connect the valve cover inlet to the intake, that eliminates any source of metered air from entering the crankcase, instead it applies VACUUM to the crankcase in 2 spots, the PCV valve & the valve cover.

Everything behind the throttle body is VACUUM.
You have to connect the valve cover inlet to something before the throttle body AND after the MAF.

 

From what I can tell he has vacuum in the crankcase with EVERYTHING DISCONNECTED to the crankcase.

I can unhook the pcv and all vacuum lines and have it immediately. It builds as it’s running and then starts with the humming noise as it pulls through the lower intake gaskets. Have redone these things 8 times and once i put a different upper and lower to make sure its not the intake.

His posts are a bit confusing causing people to go off on tangents so hopefully if he does my testing we will find out more.

ks

 

My Mechanic friend was having problems with a brand new rebuilt bbc that sounded like the engine bearings had NO lube to them... The screech was terrible...
He had nothing to do with the rebuild or install, it was just laid on his lap to fix the "screeching" noise.... This guy is one of the most competent mechanics I know and he could not figure it out....
Mechanic was just about to drop the oil pan to check the bearings when I showed up... No, I am not a master mechanic at all, but I had just read an article on PCV flow in an engine... I should say I am talking about carbureted engine here...
Car owner had a PCV in one valve cover and an airtight rubber plug in the other one that sealed it tight... I reached down and tried to pull out the rubber " oil fill " plug but it was being sucked so tight from vacuum I could not... Turned off engine, pulled the rubber plug, wallah it was fixed.... Installed a vented oil fill cap where the rubber plug was....
The screeching was the engine sucking at any spot where it could get air as the PCV valve was creating a vacuum within the entire engine..... When you say you have sucked in gaskets it reminds of this same engine as it would have surely sucked in gaskets eventually......

 

PERFECT! That's what I expected so the intake is sealed with no issues.

The "excessive" vacuum that you were experiencing was due to a vacuum line pulling a vacuum on the crankcase. From here it's a matter of getting the lines connected CORRECTLY to where they are supposed to go.

Question: At this time we will need to know what modifications to the intake and throttle body there are in order to know if the vacuum lines can be installed EXACTLY like a factory car has them or what aftermarket parts are on it so the lines can be connected correctly.

What I suspect, and what others have posted, is the PCV hose, the PCV itself, and a "fresh air vent" are not correct. So a pic of the PCV hose, PCV valve and the "fresh air" vent will help us see how the PCV system is set up.

ks

 

PERFECT! That's what I expected so the intake is sealed with no issues.

The "excessive" vacuum that you were experiencing was due to a vacuum line pulling a vacuum on the crankcase. From here it's a matter of getting the lines connected CORRECTLY to where they are supposed to go.

Question: At this time we will need to know what modifications to the intake and throttle body there are in order to know if the vacuum lines can be installed EXACTLY like a factory car has them or what aftermarket parts are on it so the lines can be connected correctly.

ks

This is crazy!! I can’t believe i have been doing this to myself!? I am a body/paint guy by the way lol. I should probably go back to the systemax intake that i had on here in the first place. But i have only the fuel regulator, brake booster, charcoal canister actuator, line that goes to dash, pcv, and oil fill that have vac lines. I do have the factory vac tree i use on the driver side apron too.

 

 

So where are you routing the hose from your Trick Flow fill tube on the valve cover?

What is your Vacuum gauge connected to? If you are connected to the crankcase and have no vacuum now, your issue is not within the intake gaskets.


As stated, the PCV system requires a LOOP with vacuum only being pulled from one side (at the PCV valve on the back of lower intake on an EFI 5.0).

Carb'ed vehicles with PCV systems simply had a breather on one valve cover (or a hose from the valve cover to the lower air filter housing), and a PCV valve on the other valve cover, with a hose from the PCV valve to the carb or intake vacuum source.

The 5.0 PCV system runs a hose from the PCV valve on the back of the lower intake to a vacuum connection on the upper intake. The inlet side is typically connected from the oil fill tube on the passenger side valve cover to a connection on the throttle body itself, or the intake tube prior to the the throttle body.

Either way, one side of the LOOP pulls vacuum, and the other side is just filtered air.


FYI, in the case of excessive vacuum in the loop pulling crankcase oil into the intake tract, oil/air separators can be installed in-line.

 

Agreed.


Again, the PCV system LOOP is rather simple:

1) Vacuum side being a hose from the PCV valve to the vacuum source.
2) Inlet side being a hose from your valve cover fill tube to filtered air prior to the throttle valve(s), and in your case post MAF sensor.

 

What year car are we working on so I can look up and understand the PCV routing?

ks

 

94

 

Here's a pic I found for the factory "fresh air" hose. As long as there is no "valve" in this line that meters fresh air then, yes, drilling a hole before the TB but after the air filter will be perfect like SLO 5-OH posted at Post #17.

ks

 

Got it…going to work on doing that tomorrow and will post my results asap! Super stoked!!🤘🏼

 

For the actual PCV "valve" you need a factory valve b/c generally they meter the amount of air that can flow through them. If you have a valve it would probably work fine, just make sure it's not a barb fitting stuck in a grommet. The system needs an actual valve.

ks

 

One way to try it is to remove the oil fill cap to let it breath good and see how it works.

Try and find out how large the stock one is and use something at least that size, larger is ok.

Also, make sure the PC valve is correct for your car.

ks