I don't remember about our GTV6's but the later V-6 cars, Milano and 164, certainly have pressure in the tank at all times as designed.

 

http://www.alfabb.com/bb/forums/alfetta-gtv6-1975-1986/52068-gtv6-gas-tank-noise.html

 

Fuel tank pressure in a GTV6 is completely normal.

 

Thanks for the link. The reason I asked was because while I've always had some pressure in the system, I've never had enough to blow the gas cap out like a champagne cork!

 

I had the same problem this past socal summer and finally remedied it with a new fuel pressure regulator. Why it worked I am not sure but my cap no longer pops off when refueling. It was so bad it broke the weld on the vapor recovery neck.

 

I developed the same problem after Oregon DEQ mandated year round ethanol use. My problems showed up in summer months. Gas tank expansion on hot days caused starting problems and loosing the cap the and performing a hot start temporary solved the problem.

Pulling up the rear carpeted deck and reeming out the metal sleeve restrictor on the fuel vapor line after the vapor / liquid separator solved my problem of vapor expansion not pushing forward to be burned by engine. (long term maintenance is to purchase pure gas or anti-ethanol additives)

 

My regulator is practically new. The again, so is my vapor valve thingy. The pressure hasn't damaged my filler neck (geez Louise, by the way), but it did blow the cap off, maybe 10 feet, when I last filled up.

 

I had the same issue with my Spider, it would blow hard when you pulled the cap and you could hear the tank creak from the pressure release. Fixed when I discovered someone had installed the relief valve in the wrong direction.

 

Renewing an old thread here.

It is summer time, so with that comes lots of fuel tank pressure. I am trying to figure out what is normal and what isn't on a GTV6. Tonight, with a nearly empty tank, I went to fill up and slowly loosened the gas cap. The pressure release was highly audible (like a backpackers camping stove if anyone is familiar) and lasted for the 8 or so seconds I spent slowly taking off the gas cap. Literally Ross Perot's "giant sucking sound" (for those old enough to remember that).

Is that normal, or do I have work to do? If not enough info, maybe next time I'll take some video and post it.

 

Nah, most likely quite normal as was with my two GTV6s. With the tank mostly empty, that's a larger air volume to hold more compressed air/fuel vapor, esp in hot weather.

I assume the car is running well.

 

I drilled a 1 mm hole in the gas cap, underneath the tumbler. It is big enough to vent the tank but not so big that it stinks. It enabled me to get rid of the canister and associated plumbing.

 

Never had a problem with my GTV6s, Milano, or the 164s. The system is designed to have that pressure in the tank for a reason.

 

See post 6. Check that capillary tube for rust or blockage. If that's clear, any pressure should flow forwards to the carbon canister and there should be minimal pressure in the tank.

 

My experience has been that there is always some after the engine has been shut off. Pressure when the engine is running? Don't know, haven't removed the cap when the engine is running.


"Got the car back on the road and pumped a few gallons with some Techron. "

Suspects it take several fillings to start to make a difference with something like Techron.

 

Maybe a little pressure but there shouldn't be much. The Spider has a check valve on the vent system that takes a little pressure to open, so it can have like 1PSI in the tank normally (which doesn't sound like much, but over the tank volume can make a bit of a hiss). The Milano doesn't have a check valve, and I don't think the GTV6 does. There's just a hose that runs fuel tank -> liquid separator tank -> carbon canister -> intake hose

When you park, any tank pressure should just vent through this hose. During running the hose/tank should be under slight vacuum from the intake hose & intake manifold (at least to the point where the inlet check valve opens and bleeds air in to compensate).

If you look in Section 4 of the service manual there's a good diagram of the system. Like I said, check that capillary tube.

 

My all original, one owner '82GTV6 has done that for, well, years. Still starts fine, runs well enough for a car with 164,000 miles.
I just remember to have my catcher's mitt with me at gas stations.

 

My two GTV6s (81,86) all had significant sounding internal tank pressure, when refueling, for all their miles, and both ran flawlessly.

 

Can someone post I diagram showing the valves to check. My 82 does the pressure thing and floods the engine when hot making starting hard . The remedy is to unscrew the gas cap releasing the pressure if you stop somewhere for a while. Without the pressure, no flooding or starting problems when hot. Just gotta remember to unscrew cap if you stop anywhere.

Would like to fix though.

 

follow link in post # 3 of this thread. Then in the referenced thread, post #8 has diagrams and resolutions. As Gubi points out, reeming out the "brass pressure regulator" between vapor recovery tank and inlet check valve will solve the problem. You will need to remove the backseat bottom and back and remove three screws holding the black carpeted deck cover to access this fuel vapor recovery system.

It is a very simple fix. Links also point out a short circuit for the charcoal canister for MY 1984 onward.

cheers.

 

Have been reading this thread,from the beginning to see what solution others might come up with.

Maybe this might help.. 1984-1987

GTV V6 Australian Cars.

Had a car that had a bad fuel smell and worse when went around RH corners with plenty of fuel in the Tank.
Thought it was the Fuel cap,,but still smell and leak of Fuel.
Then found the steel filler neck had a hole in it,so removed and welded the hole.
Then Major Pressure in the tank when fuel cap removed.after above fixed.

Someone drilled a hole in the neck to stop the pressure and the fumes appeared.

Removed that shelf behind the rear seat + cleaned out the hoses + tubes and canister,but no problem found,,but thought the problem might have been fixed,as done to the 2 litre 4 cyl cars.

Still pressure build up.

Followed the line from the back of the seat to the engine bay area.
Blew air in it= restriction,
Where it finishes at the engine= no air coming out from the back of the seat.
From the engine,followed the line to the RH Front guard==rear of front guard.
Removed the splash shield.
Oh,,another canister with lines.
Blew air from back seat area to where it went into his canister..No restriction.
Blew air into the canister and other lines and removed restrictions

Blew air from back seat hose to engine= no restriction.

Problem solved= no pressure.

Is it only Australian delivered cars or all GTV6s that have the extra canister under the RH Guard.



Hope this helps.

Robert

 

Some interesting replies above for discussion.

Problem 1 some have= fuel tank Vacuum= sucking when fuel cap released.

When fuel tank gets low in fuel,,the valve on top of the rear seat alllows air in the tank to stop a vacuum.
If vacuum exists,,fuel will find it very hard to get to the engine,,so the one way valve above the rear seat is required and no restrictions

Problem 2= pressure in the tank when fuel cap removed.

Fuel and fuel fumes do expand,,especially in hot conditions,,so when do we release the pressure.
From the fuel tank,,to the canister above the rear seat,,to the canister in the RH guard,,to the engine.

Pressure and vacuum in a fuel tank are both bad conditions to have.

Some say its normal and Ok.

I don't agree.

Your thoughts..

Its just a discussion guys,,so don't go crazy.

Robert

 

The drilled hole was too big. I drilled a 1/16" hole through the filler cap and it smelled. I plugged it and drilled a 1mm hole and it does not smell. This enabled me to get rid of the canister and a couple of hoses under the hood. I blocked off the vent tube from the tank.

 

Hi alfaparticle.

Did you do this modification due to pressure or Vacuum.
Does your car have the canister under the RH guard ?

Would you suggest others to drill a hole,or to fix it properly ?

 

Don't have much experience here... Some models of cars need a vented fuel cap that aren't obvious upon examination... swapping out caps and not taking that into account can cause all kinds of issues with pressure build up etc if they aren't right... I've even heard of carbs starving and the car dead in it's tracks over this simple matter.. Keeping an original cap (not a repop) can cross that off the list. Seems like alot of drilling and filling holes can lead to misleading trails too which might add confusing signals to the solution .. just my opinion..

 

Hi alfaparticle.

Did you do this modification due to pressure or Vacuum.

Both

Does your car have the canister under the RH guard ?

Not any more

Would you suggest others to drill a hole,or to fix it properly ?

I consider drilling a hole to be a proper fix. That is how most cars were before the government got involved.

 

It is sufficiently complex and unreliable that pressurized tanks are a common problem. It is over-engineered if you do not have to comply with emissions regulations.

 

Effect on engine performance

First off, I was wrong when I thought that my 1mm hole in the gas cap would do the trick
Second, fuel tank pressure will affect performance. I was doing WOT runs in my GTV6 today - logging the rpm, AFR, MAP and throttle position. The graphs indicated that the motor was rich so I reduced fuel and repeated the test. Whatever I did it was too rich. The problem was my gas tank was almost empty and the ambient temperature was on the rise and the pressure in the tank caused my AFR to decrease by one whole number, say from 12 to 11. I unscrewed the gas cap and the AFR went back to normal. I now have a much bigger vent!