I’ve been doing smoke tests on my fox and I’ve been through 3 different brand new EGR valves now and every one has leaked through the holes in the valve. Am I just getting that unlucky with these egr valves I’m buying or are they supposed to do that??
Mine leaked during the smoke test. Brand new NOS unit too.
First off, you’ll want to disconnect the vac line and plug it to ensure it’s not a diaphragm leak. This is a vac leak and you will need to replace the EGR valve
In terms of leaking from the internal passage of the EGR, I believe most if not all valves will probably leak this way. There’s no o-ring or internal seal where the plunger shaft passes through the body.
It's not technically a vacuum leak. Let's think about it for a second. Under normal operating conditions this EGR passageway is under positive pressure at all times. Any leak would be outwards, but it's not metered air. It's post-combustion gases which normally would be expelled through the exhaust. A slight positive pressure leak at the valve shouldnt really cause any issues because the volume of this gas is not controlled.
During the smoke test, with the engine off, the smoke travels through the vac lines into the intake and down through an open valve into the heads. The smoke will then travel up the EGR passageway to the EGR valve and eventually leak where the shaft passes through the body from the diaphragm. When the engine is running, this passageway is not under vacuum. It's under positive pressure.
I left the valve as is with the "leaking" EGR. Car runs fine.
After replacing the leaking unit the car ran perfect with no more vacuum leak. So there was no need to smoke it again.
If smoke injected into vacuum system is leaking out from somewhere other than the air filter, that is a vacuum leak. If you are doing this trying to find a leak, try running the engine with the vacuum line to the EGR removed and plugged to see if things change.