strange event

[siii8873]

Cousindave,
that's great that this post helped you. That's a great thing about this forum.
Bob

[cousindave]

Siii8873: just drilled my cap after reading this post. My rig runs much much better. I also had replaced my fuel cap with a new one that sealed too well!

[SafeAirOne]

My only concern with the hole in the cap is getting moisture in the tank over time.

Forgive me if I misunderstand the above statement, but it prompts this response:


I believe that any fuel tank that vents to the outside air poses that risk.

Note that ALL fuel tanks are somehow vented to the outside air (or else they'd all develop vacuums as the fuel is being used, as you know).

I can't think of one that uses a desiccant or other type of air dryer, so I doubt your in any more moisture danger than all the other vehicles on the road by venting your gas cap.

The non vented gas caps still had vented fuel tanks--They were just vented through a charcoal canister.

[siii8873]

My only concern with the hole in the cap is getting moisture in the tank over time.

[bkreutz]

I must have a rarity then, all the vent stuff is there. If you have a blanking plate, you could take it off, drill a hole and tap it for a barbed fitting, then run a vent hose somewhere (higher than the filler neck) and put a foam filter on the end of it. Or you could get fancy and put a valve that allows air in but doesn't allow fumes to vent out, but with my luck the first thing that would happen is the valve would get stuck closed. Or you could just leave the cap vented, They were all that way until the EPA got involved. (I'm not recommending this, just in case the "vapor police" are reading this.)

[siii8873]

I've had two SIII's and this system was gone on both of them. My first one had the hoses running behind the seat box and a canister in the wheel well behind the drivers seat and a bracket in the engine compartment where another canister was located. The supply to this system was blanked off. There are no remnants of this system on this truck just the blanking plate on the tank.
These systems were a evap system, which I have seen in the green bible but never in service on a truck. The parts are NLA and usually just blanked off (RN sells the blanking plates for this).

[bkreutz]

I did exactly as noted I drilled a small hole in the center of the inside of the cap. Still need to test drive to confirm (if there is such a thing with these intermittant things). There was enough of a vacuum in the tank that I have some confidence it could have overcome pump capabilities.
That's a good idea to get a second cap for summer.
BTW this is a SIII with the three prong sealed cap. I checked they don't make a vented cap in three prong.
Hope it all was this simple!!

How is the vent system on your tank currently configured? Stock there should be a plastic line from the tank to a canister on the drivers side of the frame, then a vent line from that forward. I would think that system is presently blocked if you're building up a vacuum in the tank, maybe you could repair (or modify) that system to function.

[siii8873]

Took the truck for a drive tonight all was well. Last time I said this the problem came back..... I think this was it this time.

[siii8873]

I did exactly as noted I drilled a small hole in the center of the inside of the cap. Still need to test drive to confirm (if there is such a thing with these intermittant things). There was enough of a vacuum in the tank that I have some confidence it could have overcome pump capabilities.
That's a good idea to get a second cap for summer.
BTW this is a SIII with the three prong sealed cap. I checked they don't make a vented cap in three prong.
Hope it all was this simple!!

[SafeAirOne]

If it's a 2-priong cap, a replacement vented cap is only $8 if you shop around.

Looking at the picture of an un-vented 3-prong cap, you may be able to drill a small vent hole through the center of the inner liner and it'll vent through the channels on the outer shell, just like the vented 2-prong cap.

[LaneRover]

Did releasing the vacuum solve your problem?

Cold would make it worse because cold air makes everything smaller (anyone who swims in the ocean off of Maine can vouch for this). Not so much the gas itself but the air in the tank really contracts.

I would try driving with the cap a bit loose - or get a 2nd cap and drill a small hole in it. That way in the summer you can still have a nicely sealed gascap.

Think of the good part of this - now you know your cap seals well!

[siii8873]

what's the best way to "vent" a newer style cap? The old style cap will not fit on SIII.

[bkreutz]

I decided to top off my tank and add some drygas as a first thing to try before I go crazy changing parts. I may have found something while doing this. When I removed the gas cap there was quite a vacuum in the tank. I had replaced the cap a while back. Law of physics can only pump out what air is allowed in. Not sure why the cold weather would make this worse. Is there a good way to vent the tank? I know the siii's originally had a vent system of hoses, charcoal canister, etc. What did the older vehicles use before this system?

They used a vented cap.

[siii8873]

I decided to top off my tank and add some drygas as a first thing to try before I go crazy changing parts. I may have found something while doing this. When I removed the gas cap there was quite a vacuum in the tank. I had replaced the cap a while back. Law of physics can only pump out what air is allowed in. Not sure why the cold weather would make this worse. Is there a good way to vent the tank? I know the siii's originally had a vent system of hoses, charcoal canister, etc. What did the older vehicles use before this system?

[jimrr]

at first it sounded like ignition prob but what you describe on the last couple pages is definatly fuel and you get enough to fill the fuel bowl but when you start working the engine it eventually runs out.........
ususally, almost always, this indicates insufficient flow to the carb. plugged intake, pump issue etc.