Had a "gross" failure of "Fuel Evaporative Controls Functional" today, and the smog tech suggested it's often a failure of a hose to the tank, but can sometimes be a failure inside the tank. Is anyone familiar with the "inside the tank" failure that can result in this error? I attempted to pull vacuum (mighty-vac) on the hose to the charcoal canister, but I can't maintain vacuum -- I'm not sure this is a valid test, either.

It's in the sig, but the truck is an '87 EFI 22R-E.

I replaced both low-pressure fuel hoses on top of the tank and will re-test. The same failure occurred two years ago, and I had a mechanic fix it -- he said he just shortened a hose by a little and it fixed it, discarding a cracked end.

 

I'm not sure where you're pulling vacuum, but that usually doesn't test anything on the evap system.

First, here's the FSM page for a '93 22re. http://web.archive.org/web/201109110...17evaporat.pdf It may give you some insight, but there are those on this forum with the correct manual for an '87.

Second, the usual problem with the evap system is that it will not hold pressure. The vented gas cap assures that the tank will never be under vacuum, but it is supposed to hold pressure (not much, like 1-2 psi). Typically, the tech will clamp off the fuel return line and try to pressurize the evap line (back to the tank). That whole system has to hold that small amount of pressure, and yours didn't.

In the Rust-Belt (not you and me), slush gets on the top of the tank and rusts out everything. Two years ago, you had a bad flex hose somewhere. You might be able to find it visually (it wouldn't surprise me if that's all it took 2 years ago), you might be able to put a little pressure on the evap line and find the leak with soapy water, but the "classic" method requires a smoke machine.

 

Ah, there's the error in my experiment. The tank is put under pressure, not vacuum. I had assumed the sound I hear when I take the gas cap off is air being sucked in, but it sounds like it's air rushing out. Thanks.

 

Correct. A correctly-working gas cap will not let the gasoline vapors out, instead pushing them into the evap cannister. But when the temps drop and the vapors condense, just a very few psi of vacuum could crush the fuel tank. There's no pollution risk by admitting air into the tank, so that's what the gas cap does to equalize the pressure.

If you have a leak in the evap line or even the fuel return line (or the top of the tank), when the tank pressurizes with rising temperature the vapors leak out into the atmosphere instead of making their way to the evap cannister. A big source of HC pollution. So our trucks get the extra-cost test of the evap system. (Vehicles built since about 1996 have their own air pump that is triggered by the computer to test the evap system on its own.)

 

So...I changed the two hoses above the tank, and the hose to the evap canister, but the tech says it still fails. Next I ran a pressure test at home with a fish tank air pump to the hose to the canister by removing it. I can pressurize it to about 1.5PSI, and it drops to 1.25PSI after 38 minutes. From what I can see on-line, the official tester will put 14in H2O pressure on the tank, and then ensure it doesn't drop more than 1in after a minute. Seems like from my test (17% drop after 38 minutes) it should pass. I've soap tested the top of the tank and the bottom of the filler & vent hoses, and no bubbles.

Do folks think my test is valid, and should be enough to pass? FWIW, this truck failed the same test two years ago, and I took it to a repair shop. All they did was shorten the vacuum hose out of the top of the charcoal canister, put some paper inside it to make it tighter to the canister, and then retested at a different shop and it passed. I'm wondering if the smog shop where it fails has an issue, or if the other shop's passing test was sketchy now.

Thoughts?

 

Well, 14 IWG (inches of Water Gauge) is about 0.5 PSI, so your fish tank pump is actually putting in 3 times more pressure than the test calls for.
I would say your test may be overdoing it a bit, buuuuuut.....
People don't realize, but 1 IWG is actually a very small amount of pressure. I used to work on a very large helium balloon, where 3.5 IWG was getting up to the danger level. I wonder if that tech is actually reading a 1 IWG drop, or if it's just a small drop when his pump stops running, or he pulls the connection to your system off. Something like that.
He should turn off his pump and wait a few seconds before checking the pressure. A 1 IWG is a very small drop, so maybe it's his testing procedure?

Just a thought...
Pat☺

 

The smog testing machines are all automated. The tech pinches the evap hose and hooks an adapter in where the fuel gap goes, and then presses the GO button. The machine then later says PASS or FAIL.

The 14in H2O pressure and 1in drop after 60s is the test the machine needs to pass to in calibration, so theoretically the vehicle's fuel system doesn't have to be any better than this at most.

And yes, my test pressure is about 3X what I think they use in the smog shop, but I don't think there's any risk with 1.5PSI on the fuel tank.

 

I would try a different smog shop. It took me a few tries to find one that is knowable, I like, and will work with me on small issues that come up.

 

Follow the evap lines all the way from the tank to the charcoal canister. There are several sections of rubber lines that span the entire run. Replace all of the rubber lines.

 

Actually, I think there's only two sections of rubber hose: at the tank, and at the charcoal canister. I believe it's hard-line from engine bay to just before the tank. And in the OP I stated that all hoses were replaced, and the system pressure-tested successfully.

Tested at another smog shop -- passed without issue. Tech says he never sees a Toyota fail the evap test. I'm writing this off to bad equipment @ the original test site.

 

Well, remember he's with us in Sunny California. My truck has lived a coddled life, but I have heard of plenty of Toyota trucks in the Rust Belt that accumulate slush atop the tank, and that can rust through everything.

 

FWIW, my baby spent the first decade of its life in the Salt Belt, but yes, it now lives in suspended animation wrt rust so it's not too awful. Plus I forked out extra $ for undercoating when new, which hopefully buys it some extra time.

But yes, not much rust here on the Left Coast. Unless you're right on the left coast, and then it's bad.