08 2500hd 6.0
Truck has code for small evap leak
Gas cap is new, smoke tested and no leaks, vent valve tested and it’s working properly. Purge valve held vaccuum and activates properly. Used scan tool to seal the system and pull a vacuum on the system. Was able to pull the vacuum down to the point the test kicked me out but it was holding vacuum. This leads me to believe there is no leak.
any suggestions?

 

best way to confirm no leak is to watch the flow meter on the smoke tester....if it zeros out after filling the system it 100% has no leak and no further test is needed to confirm this.

i believe the 08 monitor the fuel tank pressure sensor. it closes the vent, opens the purge and monitors the tank pressure....expects to see a drop of a set range....then closes the purges and monitors vacuum decay. monitor this sensor and confirm tank pressure sensor value changes.

 

The smoke machine I’m using is a cheaper one with no meter unfortunately, but I can confirm that the fuel tank pressure sensor does work

 

what is the code number

 

P0442

 

just looked over the diagnostic
vac test isn't a great way to check for leaks as if the vac is strong enough it will pull it down even with a leak present.
how many mmh20 does the sensor read with koeo and cap removed?

for giggles is the evap filter path clean and the cannister not restricted. these will effect how much vac is pulled in the tank/sensor reading.

 

To the poster of this post where is that located I may need to check mine cause I have the same issue from time to time

 

I chased something like this on my 2007 Suburban. I finally found the issue. The pins in the connector for the purge valve were loose. I took a needle and bent the pins then so they were good and tight. Problem resolved.