EVAP system expert needed.....
Thread Starter
Joined: Nov 2001
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From: Schiller Park, ILL Member: #317
There is also a vent valve in the EVAP system, located near the fuel tank, but this valve does not control vapor flow to the intake (that's the purge valve's job), so I wouldn't suspect it as the culprit if you're having a similar problem.
Time to bump this up again!!!!
Can someone let me know when the Vent solenoid gets activated?
I'd assume it's only if there's excessive tank pressure and it won't vet enough through the purge valve.
My issue is that I'm getting positive pressure in my gas tank when I have half a tank or less. I figure that it's because the remaining air gets warm thus expanding and creating enough pressure to give me a hard time. To the point where I can't put gas in the car because the check valve gets locked up, until I wait a long time with the gas cap off or stick something down into the tank (through the filler) to force open the check valve and relieve the pressure.
Any info would be great. Thanks!
Can someone let me know when the Vent solenoid gets activated?
I'd assume it's only if there's excessive tank pressure and it won't vet enough through the purge valve.
My issue is that I'm getting positive pressure in my gas tank when I have half a tank or less. I figure that it's because the remaining air gets warm thus expanding and creating enough pressure to give me a hard time. To the point where I can't put gas in the car because the check valve gets locked up, until I wait a long time with the gas cap off or stick something down into the tank (through the filler) to force open the check valve and relieve the pressure.
Any info would be great. Thanks!
TECH Senior Member
Joined: Apr 2002
Posts: 6,080
Likes: 17
From: So.Cal.
Time to bump this up again!!!!
Can someone let me know when the Vent solenoid gets activated?
I'd assume it's only if there's excessive tank pressure and it won't vet enough through the purge valve.
My issue is that I'm getting positive pressure in my gas tank when I have half a tank or less. I figure that it's because the remaining air gets warm thus expanding and creating enough pressure to give me a hard time. To the point where I can't put gas in the car because the check valve gets locked up, until I wait a long time with the gas cap off or stick something down into the tank (through the filler) to force open the check valve and relieve the pressure.
Any info would be great. Thanks!
Can someone let me know when the Vent solenoid gets activated?
I'd assume it's only if there's excessive tank pressure and it won't vet enough through the purge valve.
My issue is that I'm getting positive pressure in my gas tank when I have half a tank or less. I figure that it's because the remaining air gets warm thus expanding and creating enough pressure to give me a hard time. To the point where I can't put gas in the car because the check valve gets locked up, until I wait a long time with the gas cap off or stick something down into the tank (through the filler) to force open the check valve and relieve the pressure.
Any info would be great. Thanks!
sounds like your vent is clogged.
I wouldn't understand the vent to atmosphere being left open if the idea is to burn all the fumes via fuel delivery. What am I missing?
Thanks for the info.
i would have to look it up in my manual for the camaro to be sure, but no vent solenoids should be left open. the gas tank would never be vented to the atmosphere, that defeats the whole purpose of what the system is supposed to accomplish.
I believe there are 2 solenoids, one vent that allows fresh air into the charcoal evap box and the other solenoid at the throttle body that allows intake vacuum to pull air through the evap box and purge it of fumes. you would need both solenoids to open and have air flow through to purge it, you can't just open the throttle body solenoid and not the vent solenoid near the evap box.
I believe there are 2 solenoids, one vent that allows fresh air into the charcoal evap box and the other solenoid at the throttle body that allows intake vacuum to pull air through the evap box and purge it of fumes. you would need both solenoids to open and have air flow through to purge it, you can't just open the throttle body solenoid and not the vent solenoid near the evap box.
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Verdad Gallardo Thread Starter
Joined: Nov 2001
Posts: 34,651
Likes: 2,577
From: Schiller Park, ILL Member: #317
i would have to look it up in my manual for the camaro to be sure, but no vent solenoids should be left open. the gas tank would never be vented to the atmosphere, that defeats the whole purpose of what the system is supposed to accomplish.
I believe there are 2 solenoids, one vent that allows fresh air into the charcoal evap box and the other solenoid at the throttle body that allows intake vacuum to pull air through the evap box and purge it of fumes. you would need both solenoids to open and have air flow through to purge it, you can't just open the throttle body solenoid and not the vent solenoid near the evap box.
I believe there are 2 solenoids, one vent that allows fresh air into the charcoal evap box and the other solenoid at the throttle body that allows intake vacuum to pull air through the evap box and purge it of fumes. you would need both solenoids to open and have air flow through to purge it, you can't just open the throttle body solenoid and not the vent solenoid near the evap box.
Purge valve draws fuel vapor from the tank using intake manifold vacuum, and the fuel pump draws out fuel....both creating tank vacuum. Vent valve/solenoid should only be "venting" vacuum, not pressure.
TECH Senior Member
Joined: Apr 2002
Posts: 6,080
Likes: 17
From: So.Cal.
. . .
I wouldn't understand the vent to atmosphere being left open if the idea is to burn all the fumes via fuel delivery. What am I missing?
. . .
I wouldn't understand the vent to atmosphere being left open if the idea is to burn all the fumes via fuel delivery. What am I missing?
. . .
- fuel pump (needs atmosphere to produce correct pressure),
- re-fueling (push out air from above fuel in tank as fuel level rises),
- air equalization (allow air to enter/exit tank as fuel level drops/rises).
The charcoal canister traps and prevents fuel vapor from escaping out thru the vent.
When the engine is running, the PCM opens the purge valve (at the intake manifold)... this allows air to be drawn in thru the vent valve, into the charcoal canister (pulling the trapped fuel vapors), thru the EVAP line, thru the purge valve and into the intake manifold.
The PCM closes the vent valve to test the EVAP system and fuel tank for leaks; at all other times the vent valve is open...
i.e. when the engine is not running, the vent valve is open (the charcoal canister traps fuel vapor from the tank).
Last edited by joecar; Jul 26, 2013 at 10:09 AM.
TECH Senior Member
Joined: Apr 2002
Posts: 6,080
Likes: 17
From: So.Cal.
The vent solenoid is NO (normally open)... when the PCM is off/shutdown there is no voltage to the vent solenoid, so it is open.
The service manual specifically says that the PCM closes the vent solenoid for the purposed of testing for leaks.
TECH Senior Member
Joined: Apr 2002
Posts: 6,080
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From: So.Cal.
If the vent was blocked, then when you attempt to add fuel using the vapor trigger gas pump, there would be no place for the air above the fuel to go, it would trigger the pump to stop, and you would not be able to add fuel.
Joecar, what you're explaining is exactly what I've suspected. But more detailed and clears other things up for me. Thanks so much for that.
I seemed to have cleared things up but wanted to go through a full tank and fill up with a hot car to make sure all is well. It seems to be so far.
All I did was pull the EVAP line going into the purge solenoid (under the hood) and pull and clean the electrical connections going into the solenoid. BTW the diagram for that line is on a sticker under the hood. Can't believe I never noticed.
Also, I used a siphon pump to push air into the line and pull air out of the line. I did that to check if it was clear and to smell the fumes to check that there isn't a clog to the gas tank.
After that I haven't had a check engine light and I just refueled the tank without any back pressure. I don't know if I cleared the line or unstuck the purge valve.. but something changed. Because I haven't been able to go through a tank without a SES light or back pressure in months.
I seemed to have cleared things up but wanted to go through a full tank and fill up with a hot car to make sure all is well. It seems to be so far.
All I did was pull the EVAP line going into the purge solenoid (under the hood) and pull and clean the electrical connections going into the solenoid. BTW the diagram for that line is on a sticker under the hood. Can't believe I never noticed.
Also, I used a siphon pump to push air into the line and pull air out of the line. I did that to check if it was clear and to smell the fumes to check that there isn't a clog to the gas tank.
After that I haven't had a check engine light and I just refueled the tank without any back pressure. I don't know if I cleared the line or unstuck the purge valve.. but something changed. Because I haven't been able to go through a tank without a SES light or back pressure in months.
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Joined: Oct 2008
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From: Anaheim Ca.
Joecar, what you're explaining is exactly what I've suspected. But more detailed and clears other things up for me. Thanks so much for that.
I seemed to have cleared things up but wanted to go through a full tank and fill up with a hot car to make sure all is well. It seems to be so far.
All I did was pull the EVAP line going into the purge solenoid (under the hood) and pull and clean the electrical connections going into the solenoid. BTW the diagram for that line is on a sticker under the hood. Can't believe I never noticed.
Also, I used a siphon pump to push air into the line and pull air out of the line. I did that to check if it was clear and to smell the fumes to check that there isn't a clog to the gas tank.
After that I haven't had a check engine light and I just refueled the tank without any back pressure. I don't know if I cleared the line or unstuck the purge valve.. but something changed. Because I haven't been able to go through a tank without a SES light or back pressure in months.
I seemed to have cleared things up but wanted to go through a full tank and fill up with a hot car to make sure all is well. It seems to be so far.
All I did was pull the EVAP line going into the purge solenoid (under the hood) and pull and clean the electrical connections going into the solenoid. BTW the diagram for that line is on a sticker under the hood. Can't believe I never noticed.
Also, I used a siphon pump to push air into the line and pull air out of the line. I did that to check if it was clear and to smell the fumes to check that there isn't a clog to the gas tank.
After that I haven't had a check engine light and I just refueled the tank without any back pressure. I don't know if I cleared the line or unstuck the purge valve.. but something changed. Because I haven't been able to go through a tank without a SES light or back pressure in months.
TECH Resident
Joined: Oct 2008
Posts: 801
Likes: 1
From: Anaheim Ca.
I also found this.
In general, here are the major issues that cause fill problems on ORVR (onboard refueling vapor recovery) equipped cars:
1) Bad ICV (inlet check valve): This is a plastic check valve located on the surface of tank where the fill hose connects. It has a spring that keeps it closed, but then opens when you start pumping gas into the tank. The ICV can get stuck shut due to plastic swelling/sticking issues. The ICV assembly is generally welded to the tank, so If goes bad, you have to replace your whole tank.
2) Bad FLVV (Fill limit vent valve): This valve is located on top of the tank or is integrated into the fuel delivery module. It will allow vapors to escape the tank at all times, until you fill up the tank to full, then a float shuts off the vent hole and that triggers the fill nozzle to shut off. Much like the ICV, the FLVV has plastic and rubber components that can degrade, swell...and stick shut. If it sticks shut, you won't be able to vent the tank vapors and thus won't be able to pump gas into the tank at a high rate.
3) Vent line attached to the top of the FLVV vent port leading off the tank is clogged or plugged; sometimes it's spider webs/insects or gunk from the tank.
4) The vent line then attaches to the CVS (Canister vent solenoid) and Canister. The charcoal in the canister can get all gunked up over time and not allow vapors to pass through it any longer. The CVS is a valve that is normally open and allows tank vapors to pass through it, however it is periodically triggered by the ECU to shut- which allows pressure checks on the Evap system. The CVS can malfunction and stick shut and not allow tank vapors to escape.
In general, here are the major issues that cause fill problems on ORVR (onboard refueling vapor recovery) equipped cars:
1) Bad ICV (inlet check valve): This is a plastic check valve located on the surface of tank where the fill hose connects. It has a spring that keeps it closed, but then opens when you start pumping gas into the tank. The ICV can get stuck shut due to plastic swelling/sticking issues. The ICV assembly is generally welded to the tank, so If goes bad, you have to replace your whole tank.
2) Bad FLVV (Fill limit vent valve): This valve is located on top of the tank or is integrated into the fuel delivery module. It will allow vapors to escape the tank at all times, until you fill up the tank to full, then a float shuts off the vent hole and that triggers the fill nozzle to shut off. Much like the ICV, the FLVV has plastic and rubber components that can degrade, swell...and stick shut. If it sticks shut, you won't be able to vent the tank vapors and thus won't be able to pump gas into the tank at a high rate.
3) Vent line attached to the top of the FLVV vent port leading off the tank is clogged or plugged; sometimes it's spider webs/insects or gunk from the tank.
4) The vent line then attaches to the CVS (Canister vent solenoid) and Canister. The charcoal in the canister can get all gunked up over time and not allow vapors to pass through it any longer. The CVS is a valve that is normally open and allows tank vapors to pass through it, however it is periodically triggered by the ECU to shut- which allows pressure checks on the Evap system. The CVS can malfunction and stick shut and not allow tank vapors to escape.
