Carpokes Porsche Forum

johnb wrote: Tue Dec 02, 2025 2:55 pm It's possible but I don't think it's the most likely explanation. The AOS is connected to the j-boot, so technically yes a leak there can be a vacuum leak, but at idle the j-boot doesn't see much vacuum. The AOS has an o-ring in the oil filler cap, another one in the clip-on cap with the hose connection, and another 2 in the block connections. In theory any of these could cause a leak but I think it would be small as long as the o-ring is present. Unscrewing the oil filler cap with the engine running can make it run noticeably rough, but that's a gigantic leak.

Small leaks can make a big difference if they're downstream of the throttle plate, where the vacuum is strong.

NCGermerican wrote: Sun Dec 14, 2025 1:59 pm Revisiting this as I've finally gotten my new smoke tester (new Amazon cheapie) after my old Amazon cheapie refused to work.

I basically did a smoke test like you would a boost leak test - inject the pressurized air+smoke at the intercooler inlet. I let the smoke go for a number of minutes, but noticed that the smoke machine (with an internal air compressor and gauge, struggled to build pressure. Then, after about 5 minutes, smoke finally started to appear.....from the airbox and the turbo outlet????

I'm extremely confused with this. My small brain is trying to figure out the air pathways in the engine. How can smoke come out of the airbox (bottom section only still installed) and turbo when the smoke was introduced into the system AFTER the turbo?

The only things I can think of, where it would be possible for air to be introduced back into the pre-intercooler system:
1) Bypass valve (I have a Turbosmart TBS-TS-0203-1222 piston style BOV)
2) Thermo switch for the EVAP system (I installed a brand new, aftermarket one when I installed the new motor in August)
Is it possible to connect the vacuum lines incorrectly with this? Meaning - does it work like a check valve since one of the "bunny ears" points more at an angle?
3) EVAP control valve and/or EVAP vacuum valve
-I installed a new EVAP vacuum valve (all black plastic instead of having the clear plastic cap) about a year ago
-EVAP control valve is original w/ over 170K miles on it

Is it possible that any of these are bad (letting air/smoke through) and if so, any tips on testing them?

Tom wrote: Mon Dec 15, 2025 8:51 am

NCGermerican wrote: Sun Dec 14, 2025 1:59 pm Revisiting this as I've finally gotten my new smoke tester (new Amazon cheapie) after my old Amazon cheapie refused to work.

I basically did a smoke test like you would a boost leak test - inject the pressurized air+smoke at the intercooler inlet. I let the smoke go for a number of minutes, but noticed that the smoke machine (with an internal air compressor and gauge, struggled to build pressure. Then, after about 5 minutes, smoke finally started to appear.....from the airbox and the turbo outlet????

I'm extremely confused with this. My small brain is trying to figure out the air pathways in the engine. How can smoke come out of the airbox (bottom section only still installed) and turbo when the smoke was introduced into the system AFTER the turbo?

The only things I can think of, where it would be possible for air to be introduced back into the pre-intercooler system:
1) Bypass valve (I have a Turbosmart TBS-TS-0203-1222 piston style BOV)
2) Thermo switch for the EVAP system (I installed a brand new, aftermarket one when I installed the new motor in August)
Is it possible to connect the vacuum lines incorrectly with this? Meaning - does it work like a check valve since one of the "bunny ears" points more at an angle?
3) EVAP control valve and/or EVAP vacuum valve
-I installed a new EVAP vacuum valve (all black plastic instead of having the clear plastic cap) about a year ago
-EVAP control valve is original w/ over 170K miles on it

Is it possible that any of these are bad (letting air/smoke through) and if so, any tips on testing them?

Have a video or picture of where the smoke went in and came out? Having a hard time fully understanding those details. Maintaining meaningful pressure will be tough if valves are in overlap, and the machine doesn't have much cfm. If I'm understanding your smoke flow, it sounds like the ISV is the natural path for smoke to get back to that side of the turbo?

NCGermerican wrote: Mon Dec 15, 2025 11:16 am

Tom wrote: Mon Dec 15, 2025 8:51 am

NCGermerican wrote: Sun Dec 14, 2025 1:59 pm Revisiting this as I've finally gotten my new smoke tester (new Amazon cheapie) after my old Amazon cheapie refused to work.

I basically did a smoke test like you would a boost leak test - inject the pressurized air+smoke at the intercooler inlet. I let the smoke go for a number of minutes, but noticed that the smoke machine (with an internal air compressor and gauge, struggled to build pressure. Then, after about 5 minutes, smoke finally started to appear.....from the airbox and the turbo outlet????

I'm extremely confused with this. My small brain is trying to figure out the air pathways in the engine. How can smoke come out of the airbox (bottom section only still installed) and turbo when the smoke was introduced into the system AFTER the turbo?

The only things I can think of, where it would be possible for air to be introduced back into the pre-intercooler system:
1) Bypass valve (I have a Turbosmart TBS-TS-0203-1222 piston style BOV)
2) Thermo switch for the EVAP system (I installed a brand new, aftermarket one when I installed the new motor in August)
Is it possible to connect the vacuum lines incorrectly with this? Meaning - does it work like a check valve since one of the "bunny ears" points more at an angle?
3) EVAP control valve and/or EVAP vacuum valve
-I installed a new EVAP vacuum valve (all black plastic instead of having the clear plastic cap) about a year ago
-EVAP control valve is original w/ over 170K miles on it

Is it possible that any of these are bad (letting air/smoke through) and if so, any tips on testing them?

Have a video or picture of where the smoke went in and came out? Having a hard time fully understanding those details. Maintaining meaningful pressure will be tough if valves are in overlap, and the machine doesn't have much cfm. If I'm understanding your smoke flow, it sounds like the ISV is the natural path for smoke to get back to that side of the turbo?

I'm going to try and make a video of it and will post it on my YouTube channel. Not tonight though - I don't even think we're going to hit freezing as a high today so my unheated garage will be an icebox. We're not used to this in Raleigh.....

Should be bearable in the garage at night within the next few days. I'm going to try and block off the AOS and EVAP lines one at a time to see if smoke still passes through and I'll also see if there's a way to test the bypass valve.