‘77 280z smog test failed on fuel evaporative control funtionals

[240zadmire]

If the plumbing is tight, no leak, then blowing air from either ends (filler next or unplug hose from the charcoal canister) will have very high resistance or not able at all? 

[Dave WM]

well you will have to build pressure in the tank before very high resistance, you should not go overboard, just a few PSI really. the line from the canister could be blocked (mine was with rust on the metal line under the car) completely. This presents as a whoosh of compressed vapors when you open the fuel cap on a hot day. There is a considerable about of restriction from on that line from the canister to the overflow tank. IIRC there is a small restricter right at the end of the rubber tube near the canister that chokes down the opening, and there is a special designed device near the over flow tank as well. IF you can fill the tank with with out any issues when filling up with gas, and you get no whoosh when opening the tank on a hot day, then you likely have venting. the question is does the line from the canister to the overflow tank work as it should. Smoking out seems the only way to find a gross leak. Low pressure and smoke should find it.

 

[240zadmire]

I found the crack.  Hopefully that’s the only place.  It’s the big hose from the vent tank to the gas tank.  About 3” from the clamp.  The cut is about an inch, very clean.  Wonder how it cracked like that.  The hose is braided and I installed new.  About 18 months now.  

will try to get the test again and keep you guys posted.  Thanks for the help

and yes, 2 bicycle valves stem, soldering iron, a clear, 10’ tube with bicycle pump did the trick.

 

 

[Dave WM]

fyi I went back and looked at the fsm, the device in line between the overflow tank and the canister is indeed a check valve so you should check by injecting smoke at the fuel nozzel not the tube at the canister. You prob inject smoke at the fuel filler, should confirm that the smoke goes to tje canister line, if smokes then clamp it off and add some pressure to the tank (again at the filler neck), I would not go over just a few psi though. OR if you are pretty sure you found it I guess you could just go for a retest. 

Edited March 7, 2022 by Dave WM

[SteveJ]

And don't forget to perform this test as illustrated in the FSM.

I think if you get liquid, the test indicates failure.

[Captain Obvious]

It's pretty much the same procedure if you have to reinflate Otto.

[siteunseen]

3 hours ago, 240zadmire said:

I found the crack.  Hopefully that’s the only place.  It’s the big hose from the vent tank to the gas tank.  About 3” from the clamp.  The cut is about an inch, very clean.  Wonder how it cracked like that.  The hose is braided and I installed new.  About 18 months now.  

will try to get the test again and keep you guys posted.  Thanks for the help

and yes, 2 bicycle valves stem, soldering iron, a clear, 10’ tube with bicycle pump did the trick.

 

 

You can buy a 3/4" PEX coupling for a splice. Only a dollar at any hardware store. Use worm gear clamps or zip-ties to hold it tight.

[240zadmire]

Folks, the good news is that the car pass smog test, barely.  There seems to be still some leakage somewhere.

 

Definitely not from the canister as the technician unhook the hose and clamp tight.  It got to be somewhere around the gas tank and the vent tank.

 

one of these day, I’ll drop the tank and trouble check it.  Btw, all hoses were new, 2 years ago.

 

regards

 

[240zadmire]

Folks, 

with the current gas price seem to keep increase whenever I hit the gas station.  This gave me a great motivation to take a look at the whole fuel hoses.  I drop the tank and pay more attention to the hoses around the vent tank.  I replace all the hoses, again.  I have driven and emptied couple of tanks and noticed a nice swoosh sound when open the filler cap when the tank is close to empty.  I believe that’s the negative vacuum the fuel pump created as it pump the fuel.

I don’t smell a slightest fuel anymore.  What confirmed to me is that I’m getting more mileage for a gallon.  I used to get about 14-16 mpg and always thought that isn’t right.  Just never occurred  to me the fuel vapor could contributed to this low mileage.  Always thought vacuum leak or running rich and never able to pin point to anything definitive.  I was neglected this problem because gas prices was relatively cheap compare to today 😉

well, weather is getting hot everyday. AC is on most of the time and I’m getting 19-20mpg consistently for the last couple of fill ups.  I read somewhere people able to get 28mpg.  They must have tune the car to tip-top shape or always driving down hills 😉

 

anyway, I’m happy with the improvement and able to keep the environment a bit greener, especially my wallet is definitely greener.  That’s important these days 😉. 
 

just thought that I’d share.  I’m sure we all DIYers keep out toys tip-top shape

 

cheers