Fuel Evaporative Controls functional check results = GROSS

[Erffalotte]

1990 XLT 2.9L V6 failed smog check. It has never failed before this. All emission control systems passed but, Fuel Evaporative Controls functional check results: said GROSS.Thought It might be the fuel filler neck and replaced it. Went back for a retest and got same results. Has any one had this problem? Do I have a leak somewhere?

 

[ZMan]

This is a tough one. I haven't had to do emissions checks on my ranger for 6 years now. Where do you live that requires emissions in a 33 year old vehicle?

Did the testing facility offer any advice? You could check the vapor canistors and gas cap, there's not much to these things really.

 

[Uncle Gump]

IP addresse say Cali...

I moved you to the correct forum.

There isn't much to the EVAP system... check for a full canister.

 

[RonD]

Welcome to TRS

Get a short hose and damp rag/towel
A Helper would be good

Remove gas cap
Put hose in the opening and wrap rag around the hose to seal the gas tank
Blow into the hose
Listen for leaks

DO NOT use an air compressor for this, you WILL blow off hoses
Human lungs can generate, at most, 2psi air pressure

 

[Erffalotte]

This is a tough one. I haven't had to do emissions checks on my ranger for 6 years now. Where do you live that requires emissions in a 33 year old vehicle?

Did the testing facility offer any advice? You could check the vapor canistors and gas cap, there's not much to these things really.

I live in Sonoma county in Northern California. The gas cap is good and I also installed a new fuel filler neck.

 

[Roert42]

How are they checking the evap system? Something built into the computer with the OBDI or something else?

I’m assuming they are saying there is a major leak in the evap system, but just calling your truck Gross isn’t very specific.


If it is an evap leak you have to pull the bed and check all the hoses and connections for leaks. Not much else to it. Could use a smoke machine if you had one.

 

[4x4junkie]

How they check it (this is for 1995 & older vehicles):
What they do is clamp the vapor hose going to the charcoal canister under the hood to block it off (preferable would be to remove the hose & plug it, but some smog techs might potentially take issue with this because so much of this shit is controlled by the state and has to be done "by the book"). Then they attach a machine to your fuel tank that pressurizes it (I assume to around 2-3 PSI, but I'm just guessing), then the machine stops and sits there for a couple minutes to check that the tank does not depressurize at all. If it does, then a leak exists = fail.

A cracked filler neck hose is by far the most common culprit on these things, but another fairly common spot is the gasket around the vapor vent on the top of the fuel tank (or sometimes the vent itself goes bad). The seal around the fuel pump assembly is also another possible failure point.
As said, it'll be easiest to pull the bed off so that everything about the fuel tank is right there and easy to get at.


I modified an old gas cap (mostly just by disassembling it so that the one-way valve is exposed) that way I can press a piece of hose against it to lightly pressurize the tank and see if it holds pressure. After leaving it sit for an hour or two, I say a little prayer in my head while I press my finger on the valve and listen for it to hiss. I do this just to make sure there's no leaks before I take it in.

P.S., I was told it is best to do a smog check with a full tank. I guess the lower air volume in the tank is less likely to trigger a failure than if there's a lot more air in there.
As for "GROSS", I wouldn't have thought the evap system would be anything but "Pass" or "Fail". Did they tag your truck as a "Gross Polluter" ?