Gas tank venting (Page 1/1)
bergertime NOV 24, 02:05 PM
I finally got my 88 GT back on the road. The PO replaced the the fuel pump(earlier this year) before I got it after sitting for 20 years. It runs great and everything works as it should, except I get a ton of pressure in the gas tank. I have to leave the fuel cap loose when I Drive it or you can hear the tank popping as the pressure build and on a hot day, even not driving it, it will build a ton of pressure, I'm not talking a slight release of air, but hurricane type air movement. It's got 80,xxx original miles. My canister is good, the expansion tank looks good. I can blow air freely from the expansion tank to the canister. But I can't blow it from the line from the canister to the fuel pump. I'm a little confused. I can fill the tank just fine, so the filler vent must be working ok, so why am I building pressure? Why are there two venting lines? If one vent lines works, why do you need the other. My pump also starts to whine pretty good after about 15 minutes on a warm day and 30 minutes on a cool day (regardless of fuel level). I really don't want to drop the tank, but I'm thinking the line from the fuel pump to the to the expansion tank is clogged? I tried running a coat hanger from the expansion tank to the gas tank with no luck. I also sprayed a ton of carb cleaner in the line and blew 200 lbs of pressure in the line hoping to unclog it, with no luck.
theogre NOV 24, 04:48 PM
Factory Fiero EVAP system have free flow of air thru the canister.

If tank gets pressurized then carefully disconnect the EVAP can vent line, the biggest line, & see if problem stops.
If stops the canister is plugged very badly.

no help then...
The vent line goes to aux tank hidden in right rear next to the battery then have another line to the tank.

This Vent line has a "metered" restriction somewhere & can get plugged w/ crap/rust. I think is part of the aux tank not in the lines.

This assumes PO didn't do something dump for an engine swap or remove the EVAP canister or other "fixes" like installing F-pump wrong then sold the car knowing have problems.

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
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theogre NOV 24, 05:03 PM
Double Post.

[This message has been edited by theogre (edited 11-24-2023).]