[rcoe]

Been trying to track down a possible vacuum leak so I dug up my old smoker and started digging.

So I pulled off the intake tube just in front of the throttle body, put the bladder in and started pumping smoke. After a couple minutes smoke started coming out of the MM catch can.



So I let keep running for another 5 minutes or so. no smoke anywhere else. Pulled the filter off the catch can and it was full of smoke.

So I put the intake back together and pulled the line that goes from the procharger vacuum manifold to the catch can off at the can. I started pumping smoke through this line back toward the engine. Let it run for 5 minutes, no smoke anywhere from the engine but it was coming out of the wastegate on the bottom of the intercooler.

So I feel confident I have no intake leaks other than possibly the catch can. Now I do have the smoothboost installed and the wastegate that replaced the BOV does rest at open and stays open during idle, closing based on throttle position. I am thinking this is running correctly.

The catch can was plumbed differently when I bought the car but it smoked badly at idle so based on the best information I could find I changed it up. The large line runs to the drivers side valve cover vent and the smaller line goes to the procharger vacuum manifold. The pass. side valve cover vent goes to the OE vacuum box(?) just behind the catch can with the middle port of this box going to the end of the air filter and the 3rd port plugged.

Do I have this catch can plumbed correctly or is it the source of a vacuum leak? Or do I need to look elsewhere?

Problem I am trying to solve is a bit of rough idle and random misfires on all cylinders, only at lower rpms. Once I get on the throttle it runs great.

Thanks in advance

[rcoe]

You can see here how the rest of it is plumbed.

[Joshinator99]

It sounds like you have it right. If your smoker generated any positive pressure in the MM can, it’s job is to blow that off that pressure before it can damage your crank seal (or others) so that’s why you’re seeing the smoke. Big hose goes directly to the valve cover and small hose to vacuum.

[rcoe]

Originally Posted by Joshinator99

It sounds like you have it right. If your smoker generated any positive pressure in the MM can, it’s job is to blow that off that pressure before it can damage your crank seal (or others) so that’s why you’re seeing the smoke. Big hose goes directly to the valve cover and small hose to vacuum.

But if the small amount of pressure I am applying with the smoker is being vented out the catch can what happens with say 8lbs of boost, is that not going to be vented as well?

When King was doing my tune he kept thinking my belt was slipping but maybe I was bleeding some boost out of the catch can. I think I might need a check valve on this line that will allow it to pull vacuum but stop it from bleeding boost.

[cjperformance]

Originally Posted by rcoe

But if the small amount of pressure I am applying with the smoker is being vented out the catch can what happens with say 8lbs of boost, is that not going to be vented as well?

When King was doing my tune he kept thinking my belt was slipping but maybe I was bleeding some boost out of the catch can. I think I might need a check valve on this line that will allow it to pull vacuum but stop it from bleeding boost.

I checked my own routing and yours seems correct. There should be a check valve already on the line that goes to the intake. In my mind it should allow air to pass from the catch can to the intake, but close under boost and not allow air to pass from intake to catch can.

It should only vent the crank case, not boost from the intake. It should still "suck" air from the crankcase through the catch can under vacuum, but vent the crankcase to atmosphere under boost while closing off the line to the intake.

Hope that makes sense. Again, routing seems fine. Id check the check valve on the small line on the can. Should be in the small AN fitting on the can.

Also maybe check that the valley port, where PCV is (or was) is closed off.

[ctrlz]

Originally Posted by cjperformance

There should be a check valve already on the line that goes to the intake. In my mind it should allow air to pass from the catch can to the intake, but close under boost and not allow air to pass from intake to catch can.

I can't see the pictures here at work, but I don't recall seeing a check valve on other installations. I believe cj may be referring to the PCV valve, which operates a little differently. A check valve blocks flow in one direction. The PCV valve blocks flow in one direction, and meters flow in the opposite direction. The below diagram uses arrows to show the relative flow rates.

[cjperformance]

Originally Posted by ctrlz

I can't see the pictures here at work, but I don't recall seeing a check valve on other installations. I believe cj may be referring to the PCV valve, which operates a little differently. A check valve blocks flow in one direction. The PCV valve blocks flow in one direction, and meters flow in the opposite direction. The below diagram uses arrows to show the relative flow rates.

No not pcv, there's a check valve in the catch can exit. Says "super exit with boost check on all wild systems".

Link to instructions: https://docs.google.com/document/d/1...Id021vXYQ/edit

-6AN Super Check asm exit #2

Looks like maybe the mild systems don't have a check valve?
Do you have a "wild" or "mild" system?

[rcoe]

I think at one time the smaller fitting in the catch can did have a 1 way valve but it must not be working now.

I have a quality valve on the way which should solve this issue, but I do not think this is the cause of my underlying issue.

ctlrz,

Yes all of the ones I have seen are spring controlled that will meter air flow in one direction while allowing no flow in the other.

[cjperformance]

Originally Posted by rcoe

I think at one time the smaller fitting in the catch can did have a 1 way valve but it must not be working now.

I have a quality valve on the way which should solve this issue, but I do not think this is the cause of my underlying issue.

ctlrz,

Yes all of the ones I have seen are spring controlled that will meter air flow in one direction while allowing no flow in the other.

If the check valve isn't working... yeah, will probably solve the boost issue, but not the *potential* vacuum leak issue.

[rcoe]

Originally Posted by cjperformance

No not pcv, there's a check valve in the catch can exit. Says "super exit with boost check on all wild systems".

Link to instructions: https://docs.google.com/document/d/1...Id021vXYQ/edit

-6AN Super Check asm exit #2

Looks like maybe the mild systems don't have a check valve?
Do you have a "wild" or "mild" system?

I do not know which it has, been on the car since 2017 when the procharger was first installed so I know it is one of their older designs. But throwing an inline check valve should do the same thing.

[rcoe]

Originally Posted by cjperformance

If the check valve isn't working... yeah, will probably solve the boost issue, but not the *potential* vacuum leak issue.

Other than this there is not a vacuum leak, I pumped smoke into the engine for so long when I finally unplugged everything it looked like Cheech and Chong had stopped by.

Going to check for exhaust leaks tonight while I have the smoker out.

[ctrlz]

Originally Posted by rcoe

I do not know which it has...

From this thread, looks like "mild" has a 90 degree fitting on the can.
https://www.camaro6.com/forums/showthread.php?t=493636

[rcoe]

after digging a bit.

Can is a wild version. The vacuum side fitting on the can does have a very simple one way/pcv valve. The smoke machine just did not apply enough pressure to engage it, I would guess it requires a couple pounds and it snaps shut.

Exhaust side is sealed with no real leaks, the clamps from the headers to the mid pipes had a very small amount of leakage.

I did want to double check the vacuum side so I traced the large vacuum line from the front of the brake booster forward along the frame rail to a T where one line kept going forward toward the headlight and the other ran to the backside of the intake manifold, maybe to the hpfp. So I disconnected the line running back and ran smoke into the line going forward and smoke poured out from somewhere up by the radiator support, could not see exactly where but it was blowing right at the inside corner of the headlight.

Not sure if that is a open air vent. will need to find a schematic and see.

[ctrlz]

Originally Posted by rcoe

one line kept going forward toward the headlight and the other ran to the backside of the intake manifold, maybe to the hpfp.

My batting percentage has not been too high with this thread, but anyway...
I think one side of that T draws vacuum from the intake manifold. The part that runs up by the headlight goes to the electric vacuum pump, which is mounted next to the radiator. This ensures the brake booster always has vacuum. I would expect a check valve somewhere on that line to the intake to protect the brake booster from boosted induction pressure.