blakecharles

hello all, I'm new to the forums.
My name is Blake.

you can skip this part if you wanna
Just got my 1st camaro. I took it to get a smog (so I can get the title in my name). Every test passes with the exception on the EVAP test, I was told they started doing this in 2007. I know I'm not the only one with this problem.

The tech said the evap system would not hold pressure and suggested the problem was with the hose. He said pressure was being released somewhere (I thought the hose broke after using that clamp, I said nothing).

The way it was explained to me, when opening the gas cap, I should hear and feel pressure being released... like openinig a bottle of soda, lol. The tech is right, there is ABSOLUTELY NO PRESSURE. He told me to take it to a shop that quoted me $400. I wanted to punch him in the face.

My question to you is, what size is this hose? can I learn to replace this myself?

IrocZed

Hi Blake,
I have a 87 Z28 [ with the 700R4 ]. It has been a gift car and always smogged to 'perfection'. I failed this time on the functional Fuel EVAP test. Apparently the 'system' is not holding pressure.

I forgot to ask the tech as to how much pressure it should hold. A search here yielded that there is a blow-by vent valve remotely attached to the gas tank which allows air in when the pressure exceeds 8psi. So i think that's the benchmark for the pressure test during the Fuel EVAP test. Anything less than that would fail us. Anyone please correct if this is not so.

Then there is the definition of the fuel EVAP system in our cars. We have a vapour line from the tank to the EVAP cannister on the drivers front. The tech would normally pinch this vapour line just before it enters the cannister and apply pressure [ through an adapter ] through the filling neck.

The way i see it this test eliminates the cannister out of the equation [ good because the line from the purge valve is blocked on my car ].

Therefore the pressure can escape from the following places.
1.) leaking vapour line [ this is the line you are talking about ]
2.) the attachment [ hose ] `twixt filler neck & gas tank.
3.) the vent valve remotely attached to the tank [ i asked GM parts and this is discontinued ]; so i don't what the fix is going to be [ Parts guy asked me to look in junkyards ]
4.) leak from the fuel pump gasket or where the vapour line attaches to the tank.

I am going to apply for the test-eligibility credit from B.A.R and attempt to pinpoint the problem.

I have a general question . Can i use a tire compresor to feed pressurized air through the cannister tube [ feed air where the tech pinches it off during the EVAP test ] and try to detect the leak in the EVAP system

IrocZed

..another thing to watch for are the emmission numbers [ especially the HC ] . If HC's are on the limit of being maxed at any of the speeds [ 15 or 25 mph ]; fixing the EVAP system to pass the functional Fuel EVAP test would most probably fail the emissions [ HC test ]. This is because a corrected EVAP system will feed vapour fumes into the intake periodically enrichening the mixture. This would bring down NOX [ reduce exhaust gas temperature ]but increase HC levels.

A possible bypass solution would be to have a full gas tank [ eliminate fuel vapours out of the equation ]; fill the tank with a can of Seafoam [ or any denatured alcohol and or block the line from the purge valve internally [ s.t. it's not visible from outside ].
or run hotter plugs.