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Discussion Starter #1
Got the car back on the road and pumped a few gallons with some Techron.

The stumble/stall still happens pretty regularly. Clearly I didn't fix it, although it's running a good bit smoother! Air leak must've been part of the problem.

When I got home I unscrewed the gas cap and it literally blew off the car with a fair bit of force.

The breather valve is new, from Greg Gordon. The cap is original.

Just curious if all that pressure in the system wasn't causing some weirdness?
 

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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.
 

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Discussion Starter #5
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!
 

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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)
 

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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.
 

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Discussion Starter #8
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.
 

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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.
 

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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.
 

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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.
 

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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.
 

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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.
 

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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.
 

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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.
 

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But Mad North-Northwest
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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.
 

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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.
 

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

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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.
 

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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.
 
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