Smell raw fuel when car is parked - time for new gas cap?
 

13b 6-port
Dellorto 48dh
RB full exhaust
low press. stock gsl fuel pump

Car has been parked in the garage for about a month now, and when i'm down on the ground doing work on her I'm smelling raw gas. Sniffing around the car, its coming from the filler / cap area.

Carb smells fine. Great actually *huff puff* mmmmmm
Exhaust smells like exhaust.
Gas lines are dry
FPR is dry
Engine bay smells like an engine bay.

Gas cap smells like raw fuel.

I noticed theres a little tiny hole drilled in the center of the cap - so i figured that might be it. I pulled the cap, stuffed a rag in there, and put some silicone over the hole. I let it dry for a day.

Interestingly, while the cap was off and the tank plugged with a rag, the smell went away! I put the re-sealed gas cap back on and it smells again!

So i'm thinking - bad gas cap gasket? I think i'll be ordering a new Mazdatrix gas cap for good measure, but why the heck was there a hole in the gas cap - i thought it was supposed to be sealed?? It looks exactly like all other OEM gas caps i've seen otherwise..

Probably a PO did that because the vent system was plugged on the tank. Make sure your
vent system works or you will be trading a smell for another issue.

See when the vent doesn't vent, gas can't be sucked out after awhile and you get a lean stall.
Can be very frustrating to track down but now you've been warned!

Well its a GSL-SE, not sure if that makes a diff, but i know it has a sealed tank / cap.

I put a new cap on there - no longer smell gas. Seemed legit, so i road tripped it this weekend, put on about 200 miles, and she ran great!

By "venting system" do you mean the charcoal canister?

yes, the tank goesinta the charcoal canister

The symptom to watch for when the venting is screwed up is pressure build up on a hot day or
a vacuum hiss when the cap is removed after cruising for a long ways. Sounds like your good to
go for now.

Yah, but then isn't that how a sealed tank works?

I smell raw gas every time I drive my 7. Of course, it's usually when I back up into my cold exhaust.

Yeah, that's why there's a charcoal canister. The system is sealed, the canister connects to the fuel tank and a vacuum line to draw the vapors into the engine while running. The canister also has a vent that allows it to release pressure on a hot day. The charcoal neutralizes the gas smell so you don't notice it.

OK then everything's working the way it should. I've never heard the charcoal canister referred to as the "Venting System" but thats what the FSM is calling it as well.

So if when you take the gas cap off after driving for a few miles and a fare amount of air comes out would that mean my charcoal canister is stopped up and not venting properly?

Yep, if t he vent is working there should be no sound when you open the cap.
Air pressure on both sides should be equal.

So yeah - the first day I had only replaced the gas cap - would go pfffsh when i opened the cap. Then I replaced the known bad small vacuum tube going into the canister - no more pfffsh. AND no more raw gas. Yay!

well don't forget that the fuel pump is removing liquid from the tank and not replacing it, so there can be a small about of low pressure on in the tank, after driving. i do mean small too

My rule of thumb is if I can hear it, there's a pressure difference and a problem.

Well, glad I popped into this thread! Just learned a lot from you guys about the equal pressure necessary in the fuel system.

Glad to hear the cap solved the issue too, nice relief for your car ioTus. I'll look for that chrome trim piece tomorrow morning I promise!

kinda of an old thread, but i'm having these issues... extreme pressure under the fuel cap, and fuel smell. anyone have pics of the line to replace on the canister? and what's a reliable cap to track down?

Well I suggest just getting the OE replacement gas cap from Mazda, which you can get through a dealer, Atkins Rotary, or Mazdatrix. The cheapo caps from O'Reiley's work well too, but the gasket isnt as high quality and I doubt will last more than a year or so.

The line that I replaced on my canister was just the skinny vacuum line that jumps to the hardline. I'm still getting massive pressure build up - so I'm fairly certain my charcoal canister is clogged.

Damn boys- I ddnt know I had a problem til I read this. Cool thread-hell I might even can fix this one. Lol

Wait so how do you fix this if there is no charcoal canister? Apparently i have this problem too but my cars pretty stripped. Should i put a vacuum line to the intake manifold?

You fix it by installing the charcoal canister - that is its specific function: to vent the gas tank via manifold vacuum and eliminate the odor at the same time.

Skinny line goes to tank - thick line goes to intake mani.

You can test if the lines are clogged by blowing into them.

Almost thinking I should dig into my system now.

I never really notice pressure, but I do remember being low on fuel last week, and when I filled up I got a good whoosh from the cap.

So hot day/long drive/low fuel = normal wooshing?

Did it whoosh in or out?

In = long drive consumes fuel and lowers gas level in tank and therefore less pressure. Opening tank normalizes pressure by sucking in. Seems to me not as big of a deal as:

Out = ambient temperature increases, pressure increases as gas fumes build up (not venting), pop the cap and it normalizes by blowin gas atcha.