Ran the car with the fuel cap off and the fan fuse off (no fuse had a fp name) and no fusable links had fp written on them (surprise the fusable links aren't named) and the car never died. I unplugged the battery figuring at worse, i'll get sprayed. So with safety glasses on, I unscrewed the fuel filter the way the haynes manual says to. No spraying, just a lot of fuel running out of the filter. Ok, i'll let it drain till there is no more pressure. Fast forward 5 minutes later and there is no sign of the fuel stopping. To sum it up, all of the fuel in the gas tank drained out with no power to the pump.

Now you'd say, why didn't you just shove the new filter in there and cap it back up, you'd get messy but at least you wouldn't lose all that fuel. I'd say, I didn't expect all of the fuel in the gas tank to drain out, so i was willing to risk some fuel loss rather than smell like gas for a day. Suffice it to say, I will not make that mistake again.

What the hell is wrong with my gas tank that it would allow gravity to drain it of fuel. There was no pressure left in the lines and the pump was off. I know the previous owner changed out the fuel pump, but i'm not sure if the gas tank is original or not. I definitely know it is nothing like the haynes manual's camaro and nothing like anyone's I've read in here talking about a fan/fp fuse under the hood or under the dash in the cabin. Luckily I saved enough fuel to make it to the gas station, but I ended up losing a lot due to having to catch it in unclean containers. Also luckily i decided to change the fuel filter when my tank was below 1/8th full.

Not a happy first fuel filter change on the `92 camaro... much easier on the otherwise hard to get to grand am gt `01.

 

Mine did the same thing, no clue. I toughed it out and shoved the new filter in while the crap dripped down my arms.

 

Left the fuel cap off didn't you?
Gravity does tend to do that. That's how you drain fuids out of places such as pools, tanks etc. Start the flow and put the outlet lower than the other end of the hose/tube or in this case line. Sometimes you get lucky and the f/p will stop just so and you'll have no problems after the initial trickle.

 

Its called siphoning. Happened a little bit to me when I changed mine. The smart thing to do would be to tie a rag around your elbows so it doesn't go any further than that. I didn't do taht, but that'd be the way to do things.

 

So thats why.

 

And that concludes today's Physics lesson!

You kind of nailed it...gravity. The filter and input line are lower than the tank, it creates a natural siphon and will drain the tank.

 

duh, but why do none of the manuals and other people who have done it mention it draining the entire tank? Why is it so easy and simple and stops clean like it's "supposed to" I know gravity is why my tank drained, I want to know why mine is so different from theirs.

 

Because they left their fuel caps on, making a vacuum in the tank.

You didn't and it allowed air to displace the gas as it left the tank onto the ground, thus creating a syphon.

When you were a kid did you even stick your straw into a glass of water, put your thumb over the end and pull it out, and the water would stay in the straw? Same thing, just larger and with gas.

 

Then why do lots of people in this forum suggest taking the gas cap off to relieve the fuel pressure. Are you saying that all you need to do is remove the gas cap and all of the fuel pressure is relieved in the lines.

Now that i think about it, the people who suggest removing the gas cap to relieve the fuel pressure in the lines dont make much sense, since the gas cap would just relieve gas pressure in the tank, the lines have a totally different fuel pressure.

 

Not unless you have a vented gas cap. It's all about pressure differential, assuming non-vented cap. When you unhook the lines, pressure in the tank is greater than the atmospheric pressure. That forces the fuel out. Venting the cap more or less equalizes the pressures. Then you place the cap back on and a vacuum is created.

 

Fuel is supposed to be forced through the lines via pressure from the fuel pump, not the static pressure caused by the gas fumes in the gas tank. Fuel in the lines is pressurized by the pump, not the gas tank's pressure, that merely keeps the fuel from evaporating.

So even if you took the cap off, all that does is equalize pressure in the gas tank while the cap is off, once you put it back on, it goes back to being higher pressure than atmosphere. Thus, syphoning would still occur with the cap on, since as the pressure is lowered in the gas tank due to loss of fuel, the fuel would evaporate faster, never allowing a vacuum to exist.

So what I was saying was, the people who recommended taking the gas cap off did so saying it would remove the pressure from the fuel lines , causing the gas to not spray out under force. That it effectively would cause the engine to die if you took the gas cap off (where pulling the fuse didn't seem to cause the car to die). This is wrong, since third gens dont have pressure relief valves in the fuel lines, you have to either run the car with the pump off or just unhook the lines and bite the bullet. The gas tank's fume induced pressure has nothing to do with pushing the gas out through the tubes, since if that was the case, the pressure caused by the gas would do that whether the cap was on or not (you'd never get your vacuum) because when you put the cap back on, the gas tank increases in pressure again, not decreases, the gas will continue to evaporate and fuel will continue to spill out of the lines until it's empty.



This doesn't remove the possibility of syphoning but it does mean that if all else is equal, the cap off or cap on would not effect the syphoning, since the gas tank pressurizes . So, since obviously, it's possible to change the fuel filter without losing all your fuel, something has to be "unequal" with our two setups. Either the fuel pump is the cause of the "problem" or something else is different. It's possible that the stock pumps block flow when they're off. It's also possible some other method is at work with stock setups to block the flow of fuel. it's only a guess. I have no freakin clue what was done to this car in the gas tank when they replaced the pump and with what type of pump. All i know is apparently, getting sprayed with fuel isn't the only possible consequence for not depressurizing before taking the fuel lines apart, causing a syphon effect is another. Perhaps if i had been able to find the fuel pump fuse and run the car, the syphon effect would have never been able to occur (since syphon effects require a vacuum to be started outside of the source it's going to flow from and that would have been the fuel pump's pressure being released when i opened the lines).


Thanks for the ideas though. Basically, the moral of the story is to find the damn fuel pump fuse or relay whatever is needed to disable the fuel pump, then run the car until it dies. Now i just have to figure out how to do that.

 

Same reason lots of people on this forum cut a hole in their hatch floor so they can cut the fuel lines to pull a fuel pump and then use rubber hose to reconnect the new fuel pump without doing a thing to the lines to ensure safety.
No. The pressure would be releived in the tank.
More or less.
No, you are assuming a flash evaporation rate of the fuel and not taking into consideration the level of saturation of the atmosphere in the tank. Doesn’t happen like that.
No, as the pump would continue to do it’s thing even with the cap off (if it were still running). Cap on or off, the car would die once all the fuel in the lines was spent. You have to run the fuel out of the system. You probably did not allow enough time for the system to run it’s course.
You then open the cap to relieve any built up pressure, then you put it back on to impede the fuel flow when you crack open the line. You are not evacuating the cavity of the fumes and as such already start with a saturated atmosphere in the fuel tank. Fuel more than likely will still dribble.

As for the rest, I think I covered everything but the relief valve. Yes, the system does have one, off the tank, usually mounted on the drivers side of the car somewhere near the lca mount IIRC. Been quite a few years since I had to replace one.

hth.