The three hoses that connect to my evap vapor canister are disconnected and I want to test it. I have had serious evap emissions problems. It is easy to blow into the connector marked "purge" on the canister and I can also suck from that connector with a vacuum tool. I cannot blow or suck at all into the connector marked "tank", which is where the hose for the two fuel tank vents connect. I would think this indicates a canister failure but would like confirmation. I have not yet tested the connector marked "air", which is where the fresh air vent solenoid behind the spare tire connects to the canister.

Does the blocked "tank" connector mean a new canister is needed? Is there a way to open the canister or clean out a clog?

Also, I would like to know out of curiosity what the purpose of the second pipe that runs parallel to the fuel tank main filler pipe is. The second pipe has a smaller diameter and also ends up near the end of the main filler pipe. If the vapors generated from filling the fuel tank with gas exit through the tank vents that connect to the canister, what is the purpose of this second filler pipe?

 

Year, make, model, engine, trans, 2WD or 4WD, 2 door or 4 door? What trouble codes are in memory? I see you are in California, does the vehicle have California emissions? On the white VECI decal under the hood, it will specify 49 State, Federal, or California.


The canister is a sealed unit, no fix for it. The smaller line along the filler neck is a vent line that is used while refueling. Without it, refueling would take "forever". And yes, it is part of the EVAP system.

 

L35 4.3L Engine. M30 automatic transmission. 2 wheel drive. 4 door. The emissions sticker says "Conforms to U.S. and California regulations for 1996 model year and tier 1 certification standards in use in California..... SFI/EGR/TWC/HO2S".

History: The fuel tank was imploded from 18 down to 15 gallons when I got the vehicle years ago. I posted photos here:https://blazerforum.com/forum/2nd-ge...ploding-85275/ During this last year there has been pressure (not vacuum) escaping from the fuel tank whenever I opened the fuel fill cap after running. About a month ago stored codes "P0446: Evap Emission System Vent Control Circuit and P1441: Evap Control system Flow during non-purge conditions" appeared. Shortly thereafter the fuel tank developed a large metal fatigue flexing leak. I suspect the P1441 was caused by the fuel leak before I noticed it.

The fuel tank is now removed and will be replaced. My goal is to make sure all parts of the evaporative emissions system are working before putting in the new tank. So far I have confirmed that the solenoid air vent valve above the spare tire closes without leaking when energized (tested in situ) and is not blocked when open. It's hose to the canister was clear. There are two tank vent lines, one from the fuel pump and another from the vapor vent at the tank front, converging at a tee and then one line from the tee to the canister. The line from the tee to the canister was completely blocked and is now cleared. That alone could probably have caused the problems I've seen. I have confirmed the two lines leading to the tee are clear and the vent valve at the front of the tank lets vapor (not liquid) out and nothing back in. Remaining to be checked are the canister itself, which was the motive for this post, and then the purge line and purge valve on the intake manifold. Then I believe I can safely put in a new tank without it imploding or exploding.

Surprisingly, this vehicle has never failed a California emissions test!

Now I am trying to confirm that my vapor canister must be replaced because I cannot blow into the connection marked "tank", which is where the tank fumes vent into. In addition to what I reported in #1 above about testing the canister, I found that I could easily blow into or suck out of the canister connector for fresh air from the solenoid vent valve in front of the spare tire. When I blow in, it comes out the purge connector, which is what I would expect since air is provided to the canister through that valve when manifold vacuum is applied during a purge.

 

P1441 is the cause of the imploded tank. P1441 means that purge flow was detected during a time when it should not be purging the canister. Only two things can cause this: #1 the purge solenoid is not closing/sealing, which allows manifold vacuum into the EVAP system when the engine is running. Or, #2, the ground circuit for the purge solenoid is shorted to ground causing the valve to open whenever the ignition is in the START or RUN position.


The purge solenoid is supplied battery voltage when the ignition is in the START and RUN positions. The PCM supplies ground to the solenoid to open it, using PWM, (pulse width modulation).

Locate & repair the problem, clear all DTC's from memory, and perform the General Motors Driving Cycle. Connect a scan tool and make sure the EVAP monitor is complete. The EVAP monitor checks the entire EVAP system, including the canister.

 

Thanks, Captain, for the info. I will post my results when done.

I forgot to include an important part of the evaporative emissions system above: the gas cap. See the attached photo of the inside of mine. At the center of the "wagon wheel" is small round plastic valve attached to a spring which is attached to a rubber diaphragm. I cannot blow air into or suck air out of that valve. How is it supposed to function and how can it be tested?

 

Some research on my part has confirmed what I suspected for my 1996 (OBDII) Blazer LS, California emissions gas cap. That is, under normal operating conditions when the emissions system is not malfunctioning and there has not been an accident, nothing whatsoever is meant to pass either into or out of a properly screwed on and sealed gas cap. All normal operating pressure and vacuum relief goes through the evap vent valve up in front of the spare tire. That includes the vacuum generated by pumping gas from the tank to run the vehicle. This understanding came from the Stant #10836 replacement gas cap sales literature for my vehicle. That cap claims to have all the original factory features. It says:

"The cap prevents fuel vapors from exiting the fuel system under normal operating conditions. The cap allows an escape path for pressure in the event of an impact situation where the fuel tank has collapsed. It also permits pressure to escape if the vapor management system malfunctions. The cap allows an alternative path for air to flow into the tank if there is an obstruction in the vapor recovery or vapor management systems. It also permits the fuel system to normalize air pressure during natural vacuum situations." Does that mean driving up a mountain? I'm not sure what that last comment means, but it is certain that the cap is not meant to relieve the amount of vacuum generated inside the tank by the ECM to test for leaks in the emissions system under normal circumstances.

Since my factory cap did not prevent the implosion of my tank (earlier) or the generation of pressure every time I open the gas cap (currently), I have concluded that it is no longer providing the extra protection it was designed to provide under the extraordinary condition of a failed emissions system, which I have. It needs to be replaced even though it would work just fine under normal operating conditions after my emissions system is fixed. Anyway, no one can accuse me of just giving in to the urge to replace it without knowing that it was really necessary.

 

My fuel vapor vent valve is located on the left side of the front top of the fuel tank on my 1996 Blazer LS 4-Door California emissions vehicle. The output of this valve is connected to the line that goes to the charcoal vapor canister. This valve is not the same as the fresh air solenoid vent valve, which is above and in front of the spare tire. I tested a new fuel vapor vent valve to see how it works:

Valve right side up, bottom immersed in vapor: the valve is open and allows vapor to pass slowly out of or into the tank. If the flow is too fast, the valve closes.

Valve right side up, bottom immersed in liquid fuel: the valve closes and allows nothing to pass out of the tank, but allows vapor to pass in. This is probably to prevent liquid fuel sloshing in the tank from exiting through the valve.

Valve upside down: the valve closes and allows nothing to pass either in or out. This is probably to prevent fuel leakage in a rollover.

Whatever is inside the valve to cause it to close can be heard to jiggle shut when the valve is turned from right side up to upside down.