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Hi

I am doing some work on my sisters 92 Ford Tempo, and well it has a really bad gas smell in the car that only appears when the gas gets down to below 1/4 of a tank. When you take off the gas cap to fill the tank lots of gas vapors come out for almost a full ten seconds. I have check for leaks but can find none. I was wondering if anyone might be able to point me in the right direction to fix this problem?
 

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When I seen the post title , reminded me of a trip in the car away back when we took my in laws dog with us .That dog could fart !!!!! All the way there and back with all the windows down and head out at times when it let go .
 

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Not fuel cap, it is illegal for them on US spec models to vent to the outside, all pressure venting goes to carbon canister. Fuel cap can only vent to vacuum not pressure.

Something is wrong with the evap system in the car. Overfilling the fuel tank can do it by saturating the carbon canister with overflow fuel from a tank too full. The last airspace in tank must be preserved, the system uses that for vapor storage.
 

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Not fuel cap, it is illegal for them on US spec models to vent to the outside, all pressure venting goes to carbon canister. Fuel cap can only vent to vacuum not pressure.
I know (same here in OZ; they only have a vent that allow air into the tank so the pump can suck fuel out) but if that inlet vent fails it will sometimes effect the working of the vapour carbon canister system as it tries to suck air in through that system instead of failed cap inlet valve.

There is also a high pressure relief valve in many caps to prevent the tank rupturing in it is hit in a collision.
 

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'There is also a high pressure relief valve in many caps to prevent the tank rupturing in it is hit in a collision.'

No longer, they do everything they can to keep the fuel in tank. Pinto taught them to do that, the cars lit on fire when gas came out of the tanks. Cars now have rollover valves even to stop all venting of fuel if car flips over.

There used to be an extreme pressure cap relief valve that opened at unusually high pressure but EPA has made that even illegal. ANY fuel getting out at all even in vapor is not allowed.

The carbon canister has a one way check valve that opens (under vacuum) I believe to allow venting when the canister purge valve in engine bay opens to allow vapor to flow to the motor. Nowadays even that check is an electronic valve so two to watch now.

Fuel tank now is made to stand the pressure provided someone does not overfill it, the necessary airspace is the expansion space in extreme heat say. Barring that the overflow goes into carbon canister to fluid lug it and ruin it.

Any smell there means a flaw in piping or other in the system somewhere, can't smell it if all capped up as it should be. May need a smoke test to find it.
 

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When I seen the post title , reminded me of a trip in the car away back when we took my in laws dog with us .That dog could fart !!!!! All the way there and back with all the windows down and head out at times when it let go .

If you switch up the food on a dog they will have some foul ones. My Parents were moving with horses. My brother in law was hauling for them and the dog got into afterbirth of a new horse.. OMG she was ripping some rank ones for most of the trip. I'm glad I didn't go on that one...:muha: One time, we found a lost young dog in our neighborhood and fed it. We took it to the vet to see if was chipped. Sure enough it was but the cute receptionist thought I had the gas..:HAHA:
 

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Do check your fuel tank carefully for leaks. While researching the venting issue I came across a few reports of fuel tanks in these cars leaking at the fuel pump gasket under the seat as well as the tanks leaking at the seam and in some cases corroding and leaking. There were also reports of the steel lines under the seat cracking. Some previous owner may have cut a pump access hole like this: https://www.youtube.com/watch?v=MPGMZO85UY4 A questionable practice. If a hole must be cut it should be made a round as possible and sealed with a large round gasket/grommet.
 

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I have cut holes in both my Focus cars for fuel pump changes, but much more careful a job than the hack butchery shown in that link. My Contour has an OEM hole under the back seat but like many things Ford, incompetently done, it must be opened up another inch before you can get the pump assembly out and I did that one too. You can put a nice looking cover over the hole after done that does not look bad at all and no leaks either. It beats the crap out of yanking entire tank with as many as ten hoses or wire harnesses on it in different places, they often are damaged at pulling the tank and you will not find replacements easy now. Best way to have evap code problems there is.

I saved that vid just for pump location in case I cut a hole in mine, I use a dremel to cut a nice neat hole, usually square so it fits in easily with the corrugations in the chassis plate there.

Done correctly no issues at all, mine have done well after the work.

The gas caps are vented but for vacuum ONLY not pressure, take one apart and study the valve setup there. Here they pull and pressure test the gas caps at inspection time, they cannot leak pressure at all or an emissions fail.
 

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DOT Regs Regulations Section | Federal Motor Carrier Safety Administration

(8) Safety venting system. A liquid fuel tank with a capacity of more than 25 gallons of fuel must have a venting system which, in the event the tank is subjected to fire, will prevent internal tank pressure from rupturing the tank's body, seams, or bottom opening (if any).

(9) Pressure resistance. The body and fittings of a liquid fuel tank with a capacity of more than 25 gallons of fuel must be capable of withstanding an internal hydrostatic pressure equal to 150 percent of the maximum internal pressure reached in the tank during the safety venting system test specified in paragraph (d)(1) of this section.

(10) Air vent. Each fuel tank must be equipped with a nonspill air vent (such as a ball check). The air vent may be combined with the fill-pipe cap or safety vent, or it may be a separate unit installed on the fuel tank.
 

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Note the use of the word 'usually', there are exceptions. Also the 25 gallon tank amount. The bigger the tank the more a need to vent it.

They use HC sniffers here, if the tank cap so much as leaks the tiniest amount you fail emissions. Common to sweep the sniffer around the cap area. That includes the cap and they remove and pressure test them at inspect like I said. Cap is hooked up to a small compressor that pressurizes the cap and gasket. They do it to my '88 and '94 Tempos every year. Can't get a clean inspection without passing it.
 

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Discussion Starter #15
Hi

I checked the Purge Valve solenoid and it seems to be OK, but I have No idea how to check the EVAP charcoal canister. I figure I should check the easy stuff first before I start checking the fuel tank. I also checked around the fuel filter, the fuel rail, & the injectors. The smell seems to be coming from the front of the car and only when the car is running.
 

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Change the gas cap; they are cheap and at worse it will eliminate one possibility. (i.e. that the inlet vent on the cap has failed and it is trying to draw air in through the evap system causing the evap system to malfunction and vent gas vapours through the inlet hose in the engine bay).
 

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That leads back to the purge canister, are you sure that the purge valve is actually opening and closing?
 
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