Sanity Check: Evap Purge Valve Stuck Open?

[WhatAmIDoing]

I have a P0440 code but never paid much mind to it because no loss in fuel economy or rough running. Recently, I've been getting wild fluctuations in fuel economy. Driving the same route everyday, getting anywhere from 19-28mpg. The last few days I have heard a loud vacuum leak coming from the rear after running for 2 hours. When I remove the gas cap, hissing changes to a whistle with a loud rush of air coming from the filler neck.

ECU is reporting EFI-315 canister purge valve leakage and EFI-614 canister shut off valve flow fault.

I'm assuming since there is immense vacuum being pulled on the gas tank, then that means the evap purge valve is stuck open? Only the fuel pump (though I doubt it highly) or evap system could pull a vacuum on the fuel tank.

Is this a pretty good indicator of a failed purge valve in the always opened position? What is suppose to be the normal operating behavior of the evap system? I believe it's only suppose to be opened for a few seconds after startup and then go back closed? Is power at the valve suppose to translate to open or closed?

[RickHaleParker]

A stuck Canister purge valve would produce both of the DTCs.

During the test of the EVAP Canister shut-off valve, the Canister purge valve is pulsed. If the canister purge valve is stuck open the pressure drops too fast and the test fails.

The Canister purge valve is normally closed and opens when 12V is applied. Disconnect the wiring harness and hoses to the Canister purge valve and blow, it should be closed. If it is closed, look for a hose leak between the Canister purge valve and the Canister.

[abscate]

You suffered damage to the left fender , didn’t you? That probably took out the canister shutoff Valve

[WhatAmIDoing]

A stuck Canister purge valve would produce both of the DTCs.

During the test of the EVAP Canister shut-off valve, the Canister purge valve is pulsed. If the canister purge valve is stuck open the pressure drops too fast and the test fails.

The Canister purge valve is normally closed and opens when 12V is applied. Disconnect the wiring harness and hoses to the Canister purge valve and blow, it should be closed. If it is closed, look for a hose leak between the Canister purge valve and the Canister.

Will pull the hose and blow to test. I just don't get why there is such a high vacuum at the tank. Yesterday it was almost impossible to pull the gas cap off (which on the bright side means it's sealing good).

You suffered damage to the left fender , didn’t you? That probably took out the canister shutoff Valve

I inspected the canister and the hoses present, and all looked to be in surprisingly good shape.The tank seems to be under constant, full vacuum. I guess for that to occur both the purge and shut off have to be open?

[WhatAmIDoing]

Under what conditions are the purge valve and shut off valve suppose to opened and for how long? I just don't understand how the whole evap system is suppose to work, other than it collects fuel vapors.

[RickHaleParker]

I guess for that to occur both the purge and shut off have to be open?

Purge leaking or stuck open explains the "high vacuum". The Canister shut-off valve is normaly open it closes during some EVAP test such as Purge Valve test and the leakage test.

If the Canister shut-off valve where stuck closed and the Purge Valve stuck open, The intake manifold vacuum would suck the tank down to a low pressure. With the vent shut off, it would take a long time for the tank to return to atmospheric pressure.

It may also be just because the open Purge Value allowed the tank pressure to get so low. The time between shutting off the engine and taking the fuel cap off is not enough time even with a open Canister vent.

[WhatAmIDoing]

I guess for that to occur both the purge and shut off have to be open?

Purge leaking or stuck open explains the "high vacuum". The Canister shut-off valve is normaly open it closes during some EVAP test such as Purge Valve test and the leakage test.

If the Canister shut-off valve where stuck closed and the Purge Valve stuck open, The intake manifold vacuum would suck the tank down to a low pressure. With the vent shut off, it would take a long time for the tank to return to atmospheric pressure.

This seams to be the theory I have developed after doing a lot of reading, especially the attached pdf. I can hear a leak coming from one of the lines back by the tank, which in this case might be a good thing, as it allows the tank to return to atmospheric pressure within a couple hours. But I think your theory is correct as to why I'm getting negative pressure in the tank.

Big question, is this dangerous? Debating if I should disconnect the hose from the purge valve and plug it until I can sort this out. Also, what is the likely hood for the shutoff valve to fail in the closed position? Concerned this may be an electric issue and both solenoids are getting 12v all the time when they shouldn't.

[RickHaleParker]

Big question, is this dangerous? Debating if I should disconnect the hose from the purge valve and plug it until I can sort this out.

"Fuel tank (1)
To avoid the fuel tank deforming due to
negative pressure it has a reinforcement plate
screwed to its underside."

I am sure the engineer did the math and designed the tank and reinforcement plate for the worst case scenario.

[abscate]

Yes, disconnect the purge valve or remove the tank line and plug with a golf tee.

Hey, something useful to do with a golf tee!

[WhatAmIDoing]

Plugged off the manifold lines. Time to tear apart the evap system. Will report back with findings. Cleared codes and all that came back was P0440 (obviously).