Gas cap question ?
09-10-2013, 05:33 AM
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Positive fuel tank pressure (from fumes when the ambient temperature rises) is "vented" through the canister. The "vented" fuel tank cap only allows air in (as the fumes cool and condense), not vapors out. That's part of the reason why you get a rush of escaping fumes when you remove the cap on a warm day.
"Too much vapor" will just increase the pressure in the tank, helping the fuel pump. Until it exceeds 44psi (the tank would have exploded long before that) the fuel system is not affected. Too little pressure (a clogged vent in the fuel cap -- very rare) means the pump is pulling a little harder, but since the pump is designed to pump up to at least 44psi, adding a few psi of "vacuum" in the tank isn't likely to affect anything.
And you're right; driving without the fuel tank cap will not cause the truck to run rough. It will add considerably to the pollution emitted, though.
Positive fuel tank pressure (from fumes when the ambient temperature rises) is "vented" through the canister. The "vented" fuel tank cap only allows air in (as the fumes cool and condense), not vapors out. That's part of the reason why you get a rush of escaping fumes when you remove the cap on a warm day.
"Too much vapor" will just increase the pressure in the tank, helping the fuel pump. Until it exceeds 44psi (the tank would have exploded long before that) the fuel system is not affected. Too little pressure (a clogged vent in the fuel cap -- very rare) means the pump is pulling a little harder, but since the pump is designed to pump up to at least 44psi, adding a few psi of "vacuum" in the tank isn't likely to affect anything.
And you're right; driving without the fuel tank cap will not cause the truck to run rough. It will add considerably to the pollution emitted, though.
Last edited by scope103; 09-10-2013 at 05:35 AM.
09-10-2013, 07:20 AM
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But if you're really wondering about the canister, by all means check it. http://personal.utulsa.edu/~nathan-b...76evaporat.pdf
(If your evap system is not working, a much more likely culprit is a broken TVV. Sometimes possible to repair, but they're about $65 at the dealership.)
09-10-2013, 11:39 AM
#7
Now are we talking about a few miles like Darn I left it sit on the roof and drove away.Just lets not use a gas cap anymore ??
Big difference .
Weather get a bunch of grit and dirt in before you know it if it is raining .
I have seen driving without a gas cap take out fuel pumps and clog filters .
I always carry a extra gas cap for those distractions like really Hot women
bottom line a few miles you should be ok many more who knows how much crap might get in there.
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09-10-2013, 03:26 PM
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That's because you always fill up in the middle of the day (when it's warm). Try taking the gas cap off first thing in the morning.
But if you're really wondering about the canister, by all means check it. http://personal.utulsa.edu/~nathan-b...76evaporat.pdf
(If your evap system is not working, a much more likely culprit is a broken TVV. Sometimes possible to repair, but they're about $65 at the dealership.)
But if you're really wondering about the canister, by all means check it. http://personal.utulsa.edu/~nathan-b...76evaporat.pdf
(If your evap system is not working, a much more likely culprit is a broken TVV. Sometimes possible to repair, but they're about $65 at the dealership.)
Thanks, That is a very good guide.
09-11-2013, 03:07 AM
#9
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"Vapor Lock" is what i have heard it called. two things can happen-
A. Cant fill up gas tank past a certain point, because the vapor has no way to be pushed out. Caused by a blockage in the EVAP system. (had this happen to me)
B. I have read that under certain conditions it can some kinds of weird depressurization or something to that effect and cause the fuel pump to starve itself momentarily, causing a rough idling/driving issue.... Like i said, thats what i read when i was searching for answers to the above issue, i have no clue if that holds water (or in this case fuel) though.
A. Cant fill up gas tank past a certain point, because the vapor has no way to be pushed out. Caused by a blockage in the EVAP system. (had this happen to me)
B. I have read that under certain conditions it can some kinds of weird depressurization or something to that effect and cause the fuel pump to starve itself momentarily, causing a rough idling/driving issue.... Like i said, thats what i read when i was searching for answers to the above issue, i have no clue if that holds water (or in this case fuel) though.
09-11-2013, 01:49 PM
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No, vapor lock is something completely different. http://en.wikipedia.org/wiki/Vapor_lock A fuel line (usually at a point close to the hot engine) gets a bubble of vapor. On a carbureted engine, the fuel pump is at the engine end of the fuel line. That bubble hits the pump, and it can't pump anything. Your truck has fuel injection, the pump is in the fuel tank, so vapor lock is almost a thing of the past.
"Almost." Your truck has a pressure-up system http://personal.utulsa.edu/~nathan-b...ne/99fuelp.pdf and http://www.autoshop101.com/forms/h22.pdf in the event a bubble is formed all the way up in the fuel rail. It raises the rail pressure under certain conditions (hot-start) to improve drivability
Uh, no. The vapor is always pushed out through the filler neck (in parts of the country where we worry about air quality the gas pumps always have a "vapor recovery nozzle" to pick up those escaping vapors and put them back in the underground tank.) The canister doesn't empty unless the engine is running, so if you needed the evap system to release a full tank of vapor you could never put gas in. If someone told you that a clogged evap system meant you couldn't "fill up [the] gas tank past a certain point," well, I hope you can get your money back.
A clogged evap system can cause you to smell fuel vapors (usually on the passenger side).
The fuel pump is always under fuel, so "starving" the fuel pump just isn't an issue (until you're out of gas). But you read something and came away with some understanding; you just can't remember where you read it. That's why you can post links. Maybe someone can help explain it.
Or, maybe, I'm full of baloney. (If you've got a reference that says other than what I say, I'd sure be interested in reading it.)
"Almost." Your truck has a pressure-up system http://personal.utulsa.edu/~nathan-b...ne/99fuelp.pdf and http://www.autoshop101.com/forms/h22.pdf in the event a bubble is formed all the way up in the fuel rail. It raises the rail pressure under certain conditions (hot-start) to improve drivability
A clogged evap system can cause you to smell fuel vapors (usually on the passenger side).
Or, maybe, I'm full of baloney. (If you've got a reference that says other than what I say, I'd sure be interested in reading it.)
09-11-2013, 03:34 PM
#11
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No, vapor lock is something completely different. Vapor lock - Wikipedia, the free encyclopedia A fuel line (usually at a point close to the hot engine) gets a bubble of vapor. On a carbureted engine, the fuel pump is at the engine end of the fuel line. That bubble hits the pump, and it can't pump anything. Your truck has fuel injection, the pump is in the fuel tank, so vapor lock is almost a thing of the past.
Uh, no. The vapor is always pushed out through the filler neck (in parts of the country where we worry about air quality the gas pumps always have a "vapor recovery nozzle" to pick up those escaping vapors and put them back in the underground tank.) The canister doesn't empty unless the engine is running, so if you needed the evap system to release a full tank of vapor you could never put gas in. If someone told you that a clogged evap system meant you couldn't "fill up [the] gas tank past a certain point," well, I hope you can get your money back.
A clogged evap system can cause you to smell fuel vapors (usually on the passenger side).
The fuel pump is always under fuel, so "starving" the fuel pump just isn't an issue (until you're out of gas). But you read something and came away with some understanding; you just can't remember where you read it. That's why you can post links. Maybe someone can help explain it.
Or, maybe, I'm full of baloney. (If you've got a reference that says other than what I say, I'd sure be interested in reading it.)
Uh, no. The vapor is always pushed out through the filler neck (in parts of the country where we worry about air quality the gas pumps always have a "vapor recovery nozzle" to pick up those escaping vapors and put them back in the underground tank.) The canister doesn't empty unless the engine is running, so if you needed the evap system to release a full tank of vapor you could never put gas in. If someone told you that a clogged evap system meant you couldn't "fill up [the] gas tank past a certain point," well, I hope you can get your money back.
A clogged evap system can cause you to smell fuel vapors (usually on the passenger side).
The fuel pump is always under fuel, so "starving" the fuel pump just isn't an issue (until you're out of gas). But you read something and came away with some understanding; you just can't remember where you read it. That's why you can post links. Maybe someone can help explain it.
Or, maybe, I'm full of baloney. (If you've got a reference that says other than what I say, I'd sure be interested in reading it.)
No one is saying you are full of baloney, i'm sure as you probably know, some wikipedia and forum info is not correct or relevant, so i'm not going to waste everyone's time posting links that possibly mean nothing or that may confuse people more. I'm just speaking from experience, hoping that it might help the OP in some way. I had a clogged evap line and couldn't put gas in my tank because the nozzle kept clicking... replaced the line and volia, gas goes in the tank..
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