GM Fuel Pumps - Wires exposed in Gas Tank/No Kaboom ???

Hi Folks, Last year my 1986 cadillac Deville FWD fuel pump went out so I took apart the gas tank and the fuel pump that was in there has all the wires and connections exposed. This is the way GM fuel pumps and I
think all cars are supposed to be. Well even the New Fuel Pumps instructions shows the wiring exposed to the gasoline in the gas tank. Strange why their is no explosion. Now im thinking - Gas tanks Sweats when it gets hot and there could be on the top of the gas - or even a film of water. If the gas tank gets low on fuel - water would throw a spark from the wires and Kaboom. but is has never happened - well not that I have heard. Strange why GM and Ford submirse the fuel pump wires and all in the gas tank. But it seems to work fine - No Explosions but a PAIN IN THE ASS TO REPLACE THE PUMP !!!.
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In order to have an explosion, you have to have a critical concentration of air in the vapor phase, and you have to have a spark.
Water doesnt float on gasoline. If you had a short circuit under the surface of the gasoline or even in the water phase, nothing would happen, except you might blow a fuse.
But if you have air in the vapor phase, and a short circuit there, it WILL blow... Normally, not much air enters the fuel tank, by design. That is one reason you can get a warning lamp if you do not have the gas cap on properly.
But, take a look at the Boeing 747... a pinnacle of engineering prowess, but they have lost plane due to fuel explosions in the center tank. Nothing is foolproof
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The same amount of air enters the fuel tank as it ever did. The tank doesn't operate under vacuum except during the times when (if so designed) an OBD2 vehicle is running an evap monitor, and at that time, the vacuum is measured in inches of water. If you have 1/4 tank of fuel, rest assured, 3/4 of the tank volume will be air.

No, that's not the reason at all. By law, the tank is only allowed to vent thru the evaporative canister, if the gas cap is left loose, the evaporative system is being bypassed, allowing an alternate path for hydrocarbons to escape. Gas caps also still have a vacuum relief valve that allows air into the tank should the normal venting mechanism in the charcoal canister fail, preventing tank collapse.

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wrote:

Technically true... Not much air ever entered the tank.
The vapor pressure of the gasoline is so high, it does a reasonable job of purging the tank when you refill.

So you are saying that if you leave the gas cap loose on a late model GM product, you are not likely to get a warning light?? Why did I get one?
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I was responding to your statement that the cause of the warning light was because of air entering the fuel tank. The light comes on because the law says that hydrocarbons are not allowed to escape the fuel tank, not because of air entering it.
Why did I get one?
Because your gas cap was loose enough to allow hydrocarbon emissions to exceed the pre determined allowable level, not because air was entering.
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Is it not the case that the hydrocarbon level is high because the pressure in the tank could not be maintained, and the hydrocarbon level was excessive at the cannister?
Ill admit, I am not totally up on these, but it seems that one is a factor of the other
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Yes.
No. It is the job of the canister to store hydrocarbons.

When the Evap monitor is run, the vent valve closes and the purge valve opens, a pressure sensor mounted in the fuel module measures the vacuum level achieved, the purge valve is then closed and the vacuum decay is measured. if the vacuum level is not reached or the decay is to fast, a trouble code is set. Once the monitor is run, the vent valve is opened, the purge valve may then be open or closed depending on the operating mode of the vehicle, but when the vent valve is open, the tank is essentially vented to the atmosphere.
What happens in a climate where is is hot during the day and cold at night. Fuel that may have been 90+ degrees cools, if the tank weren't vented, the tank would collapse due to the pressure differential inside versus outside.
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Thanks for the explanation Aarcuda
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On Sat, 16 Dec 2006 14:57:52 -0600, aarcuda69062

I once left the cap off a 98 Blazer under warranty and never got the light. Took it to the dealer and they found no codes set, said it was fine. Now when I remove the cap there is no longer a whoosing sound like before. Something failed but it runs ok so I just forgot about it. wrenden
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There is no danger in having a sealed motor submerged in gasoline. The liquid is not flammable, only the vapors. Gas pumps today need higher pressure for fuel injectors than they needed for carburetors and there is a constant flow of fuel through the system.
If there is any water in the tank, it certainly won't be floating on top since oil is lighter. Nor have I ever heard of water throwing sparks. Do a little reading on the chemistry and physics of fire for a better understanding. Yes, it is a PITA to change out a pump.
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snipped-for-privacy@webtv.net (Brian Bower) wrote:

Nothing strange about it at all.

I've washed the tops of thousands of 12 volt automotive batteries with water and have never seen a spark. Not even so much as a sizzle.

Nothing strange about it at all.

That's why it's a skilled trade.
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Brian Bower wrote:

The flammability range of gasoline is between 1.4 and 7.6%. If the ratio of gasoline to air is less than 1.4%, then the mixture is to thin to burn. The mixture cannot burn when it contains more than 7.6% gasoline because it is too rich to burn.
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It is worse than that. If you would have disected the old pump you would have found a conventional DC permanent magnet motor with armature and carbon brushes. A normal characteristic of this type of motor is to have sparks of varying sizes produced at this point. The fuel actually flows over these sparking brushes in the fuel pump. While I have never consulted a definitive source on the matter, I assume there is absolutely no danger due to the fact that the fuel is normally in a liquid form with no oxygen available for combustion. But it seems to me that there might be more danger as the pump starts to suck air, such as when the fuel tank is nearing empty. But again, the fumes in the tank are probably too rich to ignite.
Live wires in the tank are nothing new, any car with an electric gas guage has been using them for decades. But it does make you think when you pull a pump and find the wiring melted leading down to it.
Lee Richardson Mech-Tech Evansville, Indiana

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To have an explosion or fire one needs the proper fuel/air ratios. Gasoline vapors burn but only if oxygen, in the proper amount, is present. Gasoline will not burn in any event.
mike

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No Kaboom ????
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