6.0PSD

Been trying to see if I can get vacuum at the fuel cap and have yet to hear it hiss... I currently have a full tank of fuel and after 30 minutes of idling and driving I go to screw out cap and nothing... Cap seal is not dry and fuller neck is smooth and clean so how long does it usually take to build up enough vacuum to hear it? Unless it is another issue that I am about to face with a vacuum leak somewhere.

salimshah

I have never heard suction or compression sound from RX fuel cap ... could be my hearing.

SC builds up pressure where the gas cap pops out.

Butane is safe to use as a test for vacuum leak.

Salim

6.0PSD

Interesting... Guess I am looking for an issue that probably doesn't exist, least I hope there's nothing wrong... Vacuum is strong at the pcv valve especially now with a cleaner valve cover, intake manifold and new pcv hose.

Been also watching for the flapper solenoid on passenger side of intake manifold to move and have yet to see it do anytging... What activates that vacuum line?

salimshah

Are you getting a CEL? or experiencing erratic high rpm on idle?

If not, you are worrying for no reason.

Salim

Baetke

Your looking for something that doesn't exist except under special circumstances. The evap system stores unburned hydrocarbon (fuel vapor) in a charcoal canister until specific driving conditions are met. Then the purge and vent valves are opened up to allow intake manifold vacuum to flush the charcoal canister and burn those vapors in the engine. A vacuum will only exist after the car is shut down and the ambient temperature drops. Since the purge and vent solenoid valves are both closed at this time a vacuum may be present due to the fuel volume in the tank contracting. This is the time when the ECU runs its small and large evap leak tests. Based on the tank pressure and temperature change the ECU can determine if the fuel system is sealed or is leaking. If you don't have a trouble code for a small or large evap leak don't worry about it.

6.0PSD

P0171 comes and goes...

P1153 and p0401 I just cleared 40 miles ago, they came up right after I installed new plugs and rear valve gaskets and have not come back so right now light has been off but am waiting for it to come back on to see what code comes up first...