I just replaced my fuel pump and sending unit this week an noticed that the gas vapor line going to the that tin can thing on the pass side of the car is plug? , i disconected both lines from it an still no air comes out , it fills with air but comes back out. is the way it works? the book is limited on this subject along with me lol thanks for any help on this )

quote Originally posted by lemonhead: ...that tin can thing on the pass side of the car

The only "tin can thing" I'm familiar with is the Cruise Control vacuum tank on the driver's side of the car/engine bay.

[This message has been edited by Patrick (edited 11-09-2019).]

Fuel expansion tank on 87-88, located outboard of spaceframe in front of passenger rear wheel liner.
It is working as designed, based on the OP's description.

Yes, 87-88 Fuel "overflow" tank is in right rear ¼ panel in front of wheel well.

No air flow likely mean lines to it are block somewhere.
I'm not sure if one tube into the tank has a "metering" hole that's way smaller then tube connected to it.
If there, The small opening maybe block w/ rust.

Older main fuel tanks has this on vent line in the tank. Not sure if is true for 87-88 main tanks or if move to overflow. If is in overflow then likely in the output to the EVAP canister.

Even w/o tube blocked, small hole can seem blocked because of limited flow.

Small hole is there to prevent Liquid fuel getting to EVAP canister because Liquid Fuel will kill them.

Try using a hand pump w/ gauge to pressure 2-4 pounds and see if pressure drops like tire w/ small leak.
Maybe could try w/ hand vac pump w/ gauge but don't try to pull biggest vacuum you can make.
If you try either, leave 1 tube open to air first. Then repeat tube sealed. Second test is to make sure overflow tank doesn't have rust holes starting to leak too.

------------------
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quote Originally posted by theogre: Yes, 87-88 Fuel "overflow" tank is in right rear ¼ panel in front of wheel well.

Another example of why it's advantageous (should actually be mandatory) for the year of the Fiero to be mentioned when advice is sought.

quote Originally posted by Patrick: Another example of why it's advantageous (should actually be mandatory) for the year of the Fiero to be mentioned when advice is sought.

Many have tried that in 20 years here alone but is ignored etc.
Even before internet... people call parts stores the want alt and so on and don't even know what model, engine, or whatever needed to say have one in stock or not.

sorry forgot to say its a 87 gt , im going to try some spraying some carb cleaner or wd-40 in the lines an let it set over night .

I don't think you will detect air movement in those lines. It is an overflow tank, so the only time air is moving would be when you are refueling.

well after some soaking with carb cleaner and a few good blast from the air gun i was able to get the expasion tank to unclog . i got alot of rusty dusty stuf an bits that came out of the othe line an it now seems to breath. Now i can connect the line to the gas tank vapor line and the other on the expansion tank to the charcoal canister and hope i pass the smog test. Thanks for the help an ideals guys, thank god we have the PFF

quote Originally posted by lemonhead: well after some soaking with carb cleaner and a few good blast from the air gun i was able to get the expasion tank to unclog . i got alot of rusty dusty stuf an bits that came out of the othe line an it now seems to breath. Now i can connect the line to the gas tank vapor line and the other on the expansion tank to the charcoal canister and hope i pass the smog test. Thanks for the help an ideals guys, thank god we have the PFF

Most Smog Test for Fiero EVAP is done on two things.
1. Tester block large line to EVAP canister then Test machine pressurize the tank. (Maybe 1 to 2 PSI max) Test machine sees air leaks then will fail. Block Overflow tank and vent lines should not matter.
2. Tester puts the Fuel cap in a adapter and does same. Problem is Often they use wrong adapter or adapter have problems.

Depending how this is reported.... some fail and don't tell you why. others will tell you 1 2 or both failed.
If 1 fails then best is a smoke test to show the air leak.
Yes, You can leak air/fumes w/o leaking liquid fuel. Very Small air leaking anywhere will often fail even if you can't smell fuel.
Harden fuel line hose to EVAP canister can fail too because testers try to clamp that hose but hard hose won't seal.

If 2 fails get new cap. If fails again the show is a new cap w/ a very recent receipt and challenge the test machine and operator. These machines are likely Decades old and little to no maintenance and the test lines/adapters wear and leak.

1 can fail for iffy test machine but harder to challenge w/o having gone thru smoke test etc.