[DonSSR]

My engine light came on and the scan showed "Evaporative emission leak". My local shop cleared the code and it came back on about three days later. It was then suggested that I change the gas cap (13 years old) because the seal looked compressed. Changed the cap and cleared the code and about 50 miles later the engine light came on again.

The tech now suggests that I have the shop do a "smoke test". Apparently they put something in the system that will cause smoke will show where there is a leak.

So... any thoughts or suggestions?

Thanks!

Don

 

[abadssr]

Inspect canister if no cracking found I would do smoke test

 

[RG]

Just did the same thing.
About the same age and miles.
New Cap, Purge Vent Valve, Evap Valve, etc.
The NEW EVAP Canister from AC Delco had a hair line crack.
AC Delco would not honor their warranty.
So, I had to buy another one and pay to have it installed twice.
Dropping the Fuel Tank is expensive.
Also the Evap Feeder Line was ruptured.
Make sure that you replace that also.
I bought 2, only need one if you need it.
Since you have to drop the tank, I would also check the fuel pump
if it is the original and the fuel filler line at the back of the fuel tank.
I did everything so all is fine now.

 

[DonSSR]

Inspect canister if no cracking found I would do smoke test

Not to sound to dumb - but where is the canister located?
Don

 

[abadssr]

Down by fuel tank I believe

 

[xoxoxoBruce]

Canister replacement instructions in the manual at:
page 6-782 Engine Controls - 6.0L
page 6-800 Engine Controls - 5.3L

 

[Bobo57]

What was the code number?

 

[Autoprof]

An actual code number would be helpful.
Smoke test pushes low pressure chemically made smoke into evap system after using a scan tool to command normally open vent valve on canister to close, thus sealing evap system. You then use a high intensity light to find the leak. Realize the evap system is designed to do self test that can find fuel vapors leaking from hole of about the diameter of the lead in a regular wood pencil. If you spend enough time and money guessing on your own you will probably fix it. The purge valve is in engine compartment and could also be the problem. You can also risk damage to fuel tank pressure sensor if you pressurize system over 1-2 psi. So you have a very small leak between fuel tank and engine allowing fuel vapors to escape. Harder to find than a slow leak in tire. You could spend time and money replace one or both valves. If still not fixed spend the money for smoke test.
Additional note self test not performed every time you drive car AND light does not come on until it fails the third time it does fail.

I also don't believe you need to lower the tank on any model year to replace canister. Look at manual as suggested by Bruce

 

[Bobo57]

0449 in my Vette was cured with new evap emissions valve.
B

 

[Roadking69]

Replace fuel tank and filler neck under warranty. I had the same problem lucky the extended coverage paid for it. Tried all the fixes and nothing.

 

[DonSSR]

Thanks everyone for your suggestions/comments! Have booked a smoke test for Wednesday unless I find the problem before then.
Don