audijim113

I had been getting a CEL (emmisions). Light came off and on for a while and I smelled gas. Changed the purge valve (new Bosch OEM) and within a few days, the CEL came back on. I didn't smell gas until I filled up the tank today.

The car doesn't feel any different and I don't think it is affecting MPG, but I probably need to replace my O2 sensors anyhow.

Getting back to the CEL and smell, what is the next step? There was some discussion of the canister. If that is the next step, is there a "how to" and a cost estimate?

audijim113

Oh, it's a 2000 A8 L

TerminA8r

Do you have any codes? It would help narrow it down.

Before you get into the canister, have you done this yet:?

1.Make sure you hear at least 3-4 clicks when closing fuel cap. Try new fuel cap.
2.Check for fuel leaks where the fuel lines connect at the rails in engine compartment.
3.In trunk on passenger side under carpet, remove 3 screws, open lid and look for leaks.

audijim113

I believe it was evaporative emmisions, incorrect purge either P0442 or P0441.

I don't think i ever tightened the cap to 3 or 4 clicks, but always thought it was tight. Just went out and blew and sucked on the cap. It holds pressure but if I suck, I can feel it release with light suction.

Of note, I had the fuel pump replaced a couple months ago and it wasn't cheap. I trust the mechanic and asked if this might have caused it. He said no, the emmisisons evaporate system doesn't connect to the fuel pump but rather it connects to the engine. Is he blowing smoke at me?

He did tell me the purge valve was sticking, He said he cleaned it and if it continued to stick and i got a CEL, the purge valve should be replaced. He didn't charge me to look at it but gave me an estimate of $250. I wasn't sure where this valve was so I posted on here, found a source for $45 bucks and changed it myself in about 20 minutes. When I took the old one out, it didn't look like it had been touched, (road dust, etc).

I was going to check the valve I took out by putting 12V on it but haven't done that. I looked at the fuel rails but didn't see any leaks.

On #3 thing you said to check "remove screws/lid in trunk", what am I looking at under this lid?

silverd2

2 different codes that "could" result in gas smell for 2 different reasons...P0441 is incorrect purge flow...if purge valve would not release pressure from gas tank vapors, they could eventually be released to the atmosphere through a back-up release valve.
P0442 is a small leak in the evap system...still dealing with the same gas vapors...could be leaking outer ring seal on the gas cap (not necessarily the gas cap check valve you tested) or any leak in one of many points (hose connections or hose breach) in the evap system...at canister, hoses to the leak detection pump, etc.

An autoparts store can read the code for free..probably P0442 (small leak), if the purge valve is OK.

The mechanic was pretty much correct...only blowing gas vapor
The fuel pump deals with liquid gas and it's hydraulic pressure through liquid lines to injectors. The evap system deals with the air space above the liquid gas in the tank and dealing with venting it to the purge valve, which releases it to be burned through the air intake circuit (intake manifold)of the engine.
So actually 2 different systems, only indirectly connected. BUT if the gasket is bad or incorrectly installed where the entire pump/level sensor assembly is inserted in the tank, there could be an evap (vapor) leak.

"#3" under the cover is the fuel pump and connections...you should not see or smell gas under here...should be totally sealed here...liquid lines AND larger outer sealing ring, which seals in tank vapors when assembly is installed...if this large seal is not perfect, it will bleed off vapor, esp when leak detection pump is activated during every start. The tank and all associated vapor lines (evap system) should not bleed off extra pressure put on them by leak detection pump too fast or leak code is produced...the system times how long the extra pressure is held.

TerminA8r

P0442: EVAP Emission Control Sys: Small Leak

"I resolved this by replacing the O-ring and cap at the top of the fuel sender unit in the trunk. This was an easy job (though I was surprised at the thick layer of dirt on top of the old one) and required part 4D0-298-135-B, which cost $15."

Always tighten fuel cap 3 or 4 clicks.

You are looking for fuel vapors, not necessarily fluid, can be hard to detect. Your nose is your friend here When you smell it go looking for the source right away.

A8CT

Most likely the seal on the sending unit in the trunk. There was a recall for this reason.

Bob

BrianC72gt

I would also check the fuel level sending unit on the right side in the trunk by removing the access cover. Three screws on the floor of the trunk up near the back of the back seat. The tank has two fuel level sending units. one all by itself on the left side, and the one you want to look at on the right side incorporated into the fuel pump assembly. When they re-install the pump, they also have to reinstall the sending unit. It is about the size of a large pharmacy pill bottle (a one foot tall pill bottle).

The top is a bitch to tighten fully. Flashlight in hand, you are looking for alignment marks, arrows, tabs or ...memory fails me at the moment...but if this isn't fully tightened, you will get fumes and a small evap release because the tank won't be a sealed system. Absent a special tool, a needle nose pliers and a box wrench to turn the pliers should do it. Just be sure to hold the needle nose pliers firmly so it doesn't slip.