Needing some help finding a vacuum leak

[Pizzarolls4]

Yup most cars run around 45kpa at idle. If you have a larger cam installed it could be lower. I chased a vac leak forever cause my car was only drawing about 55-60 kpa at idle but I have a larger cam making the engine less efficient in that range so it is normal.

Engine and everything is stock as much as it can be on a Goblin. Well I guess only "mod" I did was I have the lnk/ldk oil pan so that I could run Powells trap door setup.

 

[Rauq]

I don't have an Aeroforce gauge but it should read vacuum and boost. Less than 101kPa (absolute) is vacuum, above that is boost. Stock LSJ should make around 12psi boost which is also about 185kPa absolute.

 

[Pizzarolls4]

I don't have an Aeroforce gauge but it should read vacuum and boost. Less than 101kPa (absolute) is vacuum, above that is boost. Stock LSJ should make around 12psi boost which is also about 185kPa absolute.

Is this right?

 

[Keckster]

Is this right?

that is pretty close to what most stock cobalts run at idle. I’ve seen anywhere between -17 to -20

could be a small leak but if it’s running well at idle it should be good

 

[Pizzarolls4]

that is pretty close to what most stock cobalts run at idle. I’ve seen anywhere between -17 to -20

could be a small leak but if it’s running well at idle it should be good

I revved it a bit and don't get boost to even go to zero.
It runs well till it hits about 160° coolant temp then squeak sound appears near bell housing removing and replacing oil cap makes sound appear and disappear.

 

[Pizzarolls4]

that is pretty close to what most stock cobalts run at idle. I’ve seen anywhere between -17 to -20

could be a small leak but if it’s running well at idle it should be good

And when I remove oil cap it sounds like pressure blowing out

 

[Keckster]

This

I believe your vac hose is on the wrong fitting on the left side of your bypass solenoid. The fitting with the metal clamp things should be open and vac should be on the bottom one.

 

[Pizzarolls4]

I believe your vac hose is on the wrong fitting on the left side of your bypass solenoid. The fitting with the metal clamp things should be open and vac should be on the bottom one.

View attachment 41513

There is a top and bottom port I have on the top port and bottom I always thought was open maybe a little filter if you're lucky

 

[Keckster]

There is a top and bottom port I have on the top port and bottom I always thought was open maybe a little filter if you're lucky

Its hard to tell in the photo, is the line connected to the port with the metal clamps or the one with out them?

 

[Pizzarolls4]

Its hard to tell in the photo, is the line connected to the port with the metal clamps or the one with out them?

The one without them
I have my daily lsj and this goblin lsj I just popped the pcv line off the intake nipple on the daily and compared to the goblin there is a drastic difference in how much suction I'm feeling on my finger on the end of the hose and when I put my finger over the goblin pcv line the noise gets way louder

 

[Keckster]

The one without them
I have my daily lsj and this goblin lsj I just popped the pcv line off the intake nipple on the daily and compared to the goblin there is a drastic difference in how much suction I'm feeling on my finger on the end of the hose and when I put my finger over the goblin pcv line the noise gets way louder

Hmm ok I’m. It sure then. Sorry for the rabbit chase.

 

[Pizzarolls4]

Hmm ok I’m. It sure then. Sorry for the rabbit chase.

You're good man thanks for trying to help

 

[Rauq]

(1 atmosphere) - (17.3 inches of mercury) =
42.7 kPa doesn't really indicate a vacuum leak.

I, too, was leaning towards the supercharger bypass controls being the source of the noise. There's more potential leak points on the top end/trans side of the motor there than about any other system.

However, the oil cap symptom does seem to point back to crankcase pressure. What's on your barb at the back left side of the valve cover? Can you cover and uncover that port with your finger and get any change?

 

[Pizzarolls4]

(1 atmosphere) - (17.3 inches of mercury) =
42.7 kPa doesn't really indicate a vacuum leak.

I, too, was leaning towards the supercharger bypass controls being the source of the noise. There's more potential leak points on the top end/trans side of the motor there than about any other system.

However, the oil cap symptom does seem to point back to crankcase pressure. What's on your barb at the back left side of the valve cover? Can you cover and uncover that port with your finger and get any change?

It's hose connected with the nylon tubing DF provides then goes to the brass piece in intake tube.
If I cover the port the sound gets louder.
Is there any harm in removing the pcv valve completely? Just to test if sound goes away

 

[Rauq]

Before you pull the IM, try removing that nylon tube and cap both sides. That's the primary entry of air into the crankcase for the PCV system at idle.

I can't see the harm in removing the PCV valve as long as you're not running the car hard with it out. I believe that in addition to the check valve function, preventing boost from pressurizing the crankcase, it's also a metering orifice, reducing flow so it's not sucking stuff up out of the crankcase like crazy. Might be interesting to try that with the valve cover breather capped off too.

Full disclosure, my suggestions are just shots in the dark, suggesting stuff I know is at least related, but perhaps not rooted in an actual diagnostic method. I'm pretty well stumped so far.

 

[Pizzarolls4]

The numbers

 

[Goblinfanclub1234]

sorry if this has already been mentioned but there is a check valve where the PCV routes back into the intake. is your check valve in backwards? maybe you dont have a check valve, I only know what is there for a turbo engine.

 

[Gtstorey]

So how sure are you that there is a problem?

 

[Pizzarolls4]

sorry if this has already been mentioned but there is a check valve where the PCV routes back into the intake. is your check valve in backwards? maybe you dont have a check valve, I only know what is there for a turbo engine.

This is the valve on an lsj engine u must remove intake manifold to access it. I installed a brand new one when it was off the first time before drivetrain went in.

 

[Pizzarolls4]

So how sure are you that there is a problem?

I'm pretty sure there's a problem because of the squeaking sound which is leading to excess crankcase pressure building. When removing oil cap on and off sound appears and disappears. I also feel it's a problem because I have 2 lsj's my daily and the goblin on my daily I pulled the hose on the intake tube to feel suction amount and it's drastically different. I worry excess pressure could blow seals out and this problem is only at idle boosting and high rpms seems even riskier.