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Chasing vacuum leak, is the evap canister purge supposed to go anywhere?
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Chasing vacuum leak, is the evap canister purge supposed to go anywhere?
I’ve been chasing down a vacuum leak on a fairly new to me third gen. It’s a 1991 305 TBI. I noticed the evap canniater AIR “nipple” looks like it was gnawed off by a mouse. Is this AIR port supposed have a vacuum line coming out of it? If so, where does it go? Could this be the source of my vacuum leak?
EDIT my title says purge, but it looks like this port is labeled “AIR”
Last edited by Smykster; Apr 27, 2025 at 07:24 PM.
Re: Chasing vacuum leak, is the evap canister purge supposed to go anywhere?
My understanding is the port labeled as "air" is an inlet. Once the NC purge solenoid valve is called to open by the ECM it draws air in through this port and mixes with the fuel tank vapors via the "tank" port. Once mixed, it draws into the throttle body via the "purge" port.
Now over time I'm not sure what happens to this port. My gut is that this "inlet" bleeds off vapors under any condition and thus would create a vacuum leak 100% of the time as you may be experiencing. Having said that it's easy enough to cap the vent tube from the tank and cap the vacuum port on the throttle body to see if it makes a difference. This should not throw a fault either and should help if its a suspected vacuum leak. Probably worth checking the operation of the purge valve as well with a 9vdc battery.
Would love to hear from someone who has torn one of these apart and completed a root cause analysis to the internals and their faults/flaws, with photos....?..
Re: Chasing vacuum leak, is the evap canister purge supposed to go anywhere?
Originally Posted by bennettcvcu
My understanding is the port labeled as "air" is an inlet. Once the NC purge solenoid valve is called to open by the ECM it draws air in through this port and mixes with the fuel tank vapors via the "tank" port. Once mixed, it draws into the throttle body via the "purge" port.
Now over time I'm not sure what happens to this port. My gut is that this "inlet" bleeds off vapors under any condition and thus would create a vacuum leak 100% of the time as you may be experiencing. Having said that it's easy enough to cap the vent tube from the tank and cap the vacuum port on the throttle body to see if it makes a difference. This should not throw a fault either and should help if its a suspected vacuum leak. Probably worth checking the operation of the purge valve as well with a 9vdc battery.
Would love to hear from someone who has torn one of these apart and completed a root cause analysis to the internals and their faults/flaws, with photos....?..
what a great response! So it seems the gnawed off bit on mine is number 2 in the diagram. If I’m reading that correctly, it pulls ambient air from the engine bay when the purge solenoid is turned on. So it seems that the number 2 inlet is always “open” which means the damage probably isint doing much of anything, right?
