Mystery Vacuum Line - Can someone check theirs?

[03Alerosil]

That's interesting cuz when mine broke I code an emissions code for a small leak. Fixed it with some rubber vacuum hose. Simple and easy repair.

[a.graham52]

Originally Posted by 03Alerosil

That's interesting cuz when mine broke I code an emissions code for a small leak. Fixed it with some rubber vacuum hose. Simple and easy repair.

Hate to say it but no u didn't. If that line breaks it does not effect evap. If anything it would set bank 1 lean codes.

Now if u had a crack in your purge line and sealed that... That would do as u discribed.

[03Alerosil]

Originally Posted by a.graham52

Hate to say it but no u didn't. If that line breaks it does not effect evap. If anything it would set bank 1 lean codes.

Now if u had a crack in your purge line and sealed that... That would do as u discribed.

Yes I did. It was a P04.... code. I am in my second year of tech school and know what I saw on the scan tool.

[a.graham52]

Originally Posted by 03Alerosil

Yes I did. It was a P04.... code. I am in my second year of tech school and know what I saw on the scan tool.

And I'm in my 8th year as a full time GM tech. Plus two years at GMASEP. The only relation between the vacuum line in question (unless previously hacked up) and the purge valve/evap system is the intake manifold there attached to.

The evap system only has ONE line in this particular system and it goes between the purge valve and fuel tank. Vacuum is only applied when the purge valve is open. Manifold vacuum Does not effect the evap system and has no other means of being introduced other then through the purge valve.

Large and small leak tests are performed when our ecm seals the purge valve with vacuum inside the tank. The ecm monitors the tank pressure through the fuel tank pressure sensor and determines a leak when vacuum is lost within a set amount time. The ecm can also set another code for flow during non-purge which happens when the ECM sees vacuum increasing in the fuel system and the purge valve is commanded off.

To put it simply. Leak test are only performed inside the fuel tank/evap system. A leak outside of the evap system (vacuum signal lines, manifold leaks, ect) have no effect on the evap system diagnostics.