BOSSFC

iTrader: (2)

Still trying to pass DE inspection on my 1990 N/A FC which runs great but can't make state inspection for emissions and fuel tank pressure. The techs at motor vehicle tell me that my tank is not holding pressure.

The way they test is by clamping the lines at the top of the charcoal canister then use a device to pressurize at the fuel cap area.

In order to fix this i blew air into the line at the charcoal canister that goes to the fuel tank and followed the line back and checked for leaks. Around the check and cut valve there was a leak on the line that goes back towards the front of the car (which I assume is the normal pressure relief area anyway) so I plugged this up and could no longer feel any leaks.

When I went back they still failed me for the tank not holding pressure. The tech tells me it is like when it is a hot day and I release my fuel cap it hisses. I have owned 3 FCs now and none of them ever hissed did nor have I ever had this problem with inspection. It would be great if anyone has ever solved this problem to give advice or comments, even a quick fix just to get me to pass is fine.

Thanks.

j9fd3s

iTrader: (3)

yeah they are doing this in CA too. did they get the right line? the only difference between the FC and every other us emission car made since 1967 is that the line to the tank is the small one.

in CA they put pliers on that line, and then take the gas cap off and put the pressure thing on the gas cap, so it can't be the gas cap (we test that separate)

i haven't had one fail yet, but step 1 is to go look at the pic/diagram of the system, there aren't that many places it can leak from.

BOSSFC

iTrader: (2)

I was suspicious of them clamping the right line I was sitting in the car when they did the test both times, but now that I think about it they were clamping from the passenger side of the vehicle. Next time I go back I will step out and make sure, I will be upset if this is the case, but glad to find out the problem.

j9fd3s

iTrader: (3)

the big line goes to the engine, clamp that and it'll fail.

i only noticed it, cause we rigged a 10ae to pass, and i just ran the big line to nothing! it was just tucked behind the intake, and he went to go clamp that, i was like NOOOOOOOOOooooooo!

clamp small line, passed the vacuum test!

toplessFC3Sman

iTrader: (1)

So... the tank is supposed to pressurize? I noticed that my tank seems to draw a vacuum since it seems to get more severe if I fill up when the gas level is lower. I've never actually checked whether air is blowing out or being sucked in, but my other car ('06 Saab) doesn't make any noise or seem to build up any pressure.

j9fd3s

iTrader: (3)

its supposed to be sealed, and the vapors are stored in the charcoal canister and either returned to the tank, or burned by the engine.

toplessFC3Sman

iTrader: (1)

Yea, thats what I thought; that any increase in pressure would force the fumes through the charcoal canister and into the intake (not just vent them); not that the tank would actually pressurize. I need to check if my charcoal canister is clogged up then.

j9fd3s

iTrader: (3)

ive never really tested it, but i think on a hot day, it'll be pressurized.

a plugged charcoal canister will do weird things too, the fuel basically is being replaced by air, and if it cant do that, it'll stop pumping fuel. if the canister was plugged you'd know it. ive never seen an FC canister plug, but ive seen other cars do it, symptoms are really weird

BOSSFC

iTrader: (2)

Thanks - j9fd3s next time I went I found out they were clamping the wrong hose and I passed no problem.

Also In order to pass emissions I bought a new cat and rerouted the air pump straight to the split air pipe and passed emissions as well.