Typo or error in FSM?

[sdnative]

I tested my Charcoal Canister according to the tests in the FSM.

IH8MUD Forum - View Single Post - No power at altitude

It tested bad. My results are:

Per the FSM: Blow into the Tank pipe and air should flow without resistance out the other two.

My test: Blow into Tank pipe and air did NOT flow out of other pipes at all.


Per the FSM: Blow into Purge pipe and air should NOT flow out of other pipes.

My test: Blow into Purge pipe and air did NOT flow out of Tank pipe but did flow freely out of bottom vent line.

I didn't have access to the low pressure air supply specified, but I just blew into the hose as softly as I could, generating what I think would be less than 2.5 psi.


Does this make sense? It would almost be correct if you switched "Purge" and "Tank" in the FSM tests.

I found another low mileage one and asked the same test be performed, and it failed also.

Could there be an error in the FSM regarding this test, or is it just that common for these to fail?

 

[Jeeper]

It's not a typo, you should be able to blow into the tank pipe and have air come out the other pipes. As you may have seen, the FSM shows how to clean the canister by blocking the purge pipe and using compressed air in the tank pipe venting out the bottom.

There is at least one check valve inside the canister. I had limited success spraying carb cleaner into the tank and purge ports, and using compressed air repeatedly to free one up. Although, I'm still not sure that the canister can keep up with the fumes. I suspect the purge valve VCV isn't opening enough to purge the canister completely. Either that or these canisters were under-designed.

It's a common failure point and they cost north of $200 new. I've never heard of a canister failure in a Chevy or Ford, but they seem to fail often on 80s.

 

[azTony]

So what kind of problems are seen with a bad canister?

 

[sdnative]

The problem I am having is the gas tank is overpressurizing at altitude. I am suspecting the CC.

I am getting less than normal mileage, which may also be related to the CC.

 

[Brentbba]

The problem I am having is the gas tank is overpressurizing at altitude. I am suspecting the CC.

I am getting less than normal mileage, which may also be related to the CC.

HMMMMM........

Had horrible, horrible gas smell last summer up at Monache Meadows (altitude). As best we could tell the gas smell was around the CC in the engine bay. Opened the gas cap and had an enormous amount of pressure release and the sound like gas bubbling, almost like it was boiling! I've never tested the CC tho.

Sound similar to what you are experiencing?

Curious as I'm headed to Tahoe with the in September and don't want issues as she hates the beast anyway. :whoops:

One more thing to test this weekend after I install the used VAF I just purchased.

 

[sdnative]

Had horrible, horrible gas smell last summer up at Monache Meadows (altitude). As best we could tell the gas smell was around the CC in the engine bay. Opened the gas cap and had an enormous amount of pressure release and the sound like gas bubbling, almost like it was boiling! I've never tested the CC tho.

Sound similar to what you are experiencing?

Yes, exactly.

Others in my group smelled gas, so I stopped to investigate. Strong gas smell coming from the gas cap area. Removed the cap and the tank vented for a couple of minutes, then I could clearly hear the gas boiling in the tank.

This has only happened in Big Bear (7000+ ft) and not in lower elevations. What altitude is Monache Meadows?

 

[Brentbba]

Yes, exactly.

Others in my group smelled gas, so I stopped to investigate. Strong gas smell coming from the gas cap area. Removed the cap and the tank vented for a couple of minutes, then I could clearly hear the gas boiling in the tank.

This has only happened in Big Bear (7000+ ft) and not in lower elevations. What altitude is Monache Meadows?

OMG - exactly. Elevation of the meadow is 7850.

Dana Adams smelled mine. Thought his nose was only for diesel, but he and all of us smelled the gas. Thought the darn gas tank was going to explode from the boiling gas. I thought gas caps were designed to vent excess pressure too! There certainly was enough to do that.

I'll test my CC this weekend and let you know what I find. I think I can get my compressor output setting down low enough for the test you couldn't do.

 

[sdnative]

The tank is supposed to maintain some low amount of pressure. The CC is designed to vent the tank (by absorbing the gas and venting pressure to ATM) if the pressure gets too high. The engine will draw out the gas into the engine to be combusted through the purge port over time. So the CC really acts as a holding buffer for gas until the engine can purge it.

If the tank draws a vacuum, the gas cap contains a one-way valve to let fresh air into the tank.

At least this is how I believe it works...