This is my first Saturn. It has had this problem for a while now. It runs out of gas at 3/4 tank. You can only add a couple gallons and the tank is full. The tank looks perfect and not bent up. When you add gas the car will start up but runs rough for a minute or so. You have to press on the gas pedal until it smooths out. It does have the check engine light on. Error code p0449. I have changed the purge solenoid. The light has not gone off. It's been six months since I changed it. Any ideas?

 

When's the last time you changed the fuel filter?

 

My daughter had it replaced about a year ago. It was doing this before she had the filter changed

 

This is only a best guess. I suspect a leak in the fuel pump assembly that would allow it to draw air instead of fuel

 

Do you hear a full tank sloshing around in the tank if you rock the back of the vehicle up and down?

Might the tank only have a few gallons in it?

Traditionally, the Evap tests are only run if the tank is between 1/4 and 3/4 full. The question then becomes where does the ECM get the fuel level from? The same signal that drives the gas gauge?

Maybe the code set when the tank was actually between one and three quarters full. The code set, but even though you replaced the part, the tank dropped below 1/4 and the Evap test routine has not run since.

I suspect there is an issue with the EVAP vent valve/solenoid. or the EVAP charcoal canister.

The EVAP vent valve is normally open and lets fuel vapors from the tank get absorbed by the charcoal canister.

The solenoid only closes the valve during the test cycle when the entire system is closed and pressurized.

However if the vent valve sticks closed or gets clogged (functionality stuck closed), the air in a mostly empty gas tank has nowhere to go when you try to fill the tank w gas. The result: tank pressure builds quickly and triggers the pressure cutoff switch on the gas pump. If you wait for the pressure to bleed off, you should be able to add more fuel until the same thing occurs.

There is an internal fuel pressure sensor inside the tank that is monitored during the Evap tests to detect system leaks.

You MAY be able to monitor that pressure sensor with a scanner that provides real time data. The only question is whether or not that pressure sensor is being red when the EVAP tests are not being run. I do not know the answer.

If data for the pressure sensor or available, you could put the key in run, monitor the PID for the fuel pressure sensor while a buddy tries to fill the tank like normal.

The other common culprit is that the EVAP charcoal canister timer designed to absorb gas vapor, actually ends up full of liquid gasoline phone too many attempts to top off the gas tank. So if the EVAP vent is functioning properly, a canister full of liquid gasoline cannot absorb the air and vapors from the gas tank that are pushed forward in the system when you try to fill gas into the tank.

I believe someone else should come along and explain how to test and determine which one is the issue. Based on the fact that you have not thrown a code for the EVAP vent, I suspect it is the canister but don't quote me on that. The purge solenoid code might have actually been triggered bye the presence of the fuel in the canister.

But now I am totally guessing and we'll stop.

I expect someone else will come along to help you narrow down which of the two scenarios is the most likely or whether there is another scenario and I am way off.

 

There is also some kind of gas cap issue with these vehicles. Not sure if that's causing your problem or not. But it does trigger codes. It's been about a year and a half since I got the car so I can't remember everything or the exact code numbers. But I do believe maybe more or less severe depending on the vehicle possibly like rolling the dice. Because mine didn't cause any major problems but I did try a couple different gas caps that fit and didn't have any more codes after that.

 

On a side note based off of what I know in General on how things work oh, I have a little Theory or idea popped in my head. Now if someone was to let this gas cap issue go for a long time. It will be constantly running a sensor or Monitor and trying to tell the owner has something's wrong here I need fixed. Now seems to me that something like a sensor or monitor is not supposed to be running all the time. So it kind of makes sense that maybe it's messed up your computer or burned out the sensor. Basically if you're running something constantly that only supposed to engage periodically or when needed eventually it's going to wear out. I think this is an example of how something simple may actually cause a bigger problems and then you're stuck figuring out what's wrong and then possibly even when you fix it it's not fixed or you keep having problems periodically. Hopefully this is somehow helpful to you or anyone else

 

Depends on what device and what its functionality is.

The evap test is run over and over when the car is moving and has between three quarters and one quarter of a tank of gas. This is done to ensure that any leak is immediately detected since the point of the whole system is to not let fuel favors escape into the atmosphere. So in this case, the test is constantly run by Design.

But to your point not true for everything.

 

Thank you for adding to this derf. I was following basic mechanical logic with that tangent. It was kind of weak I was grasping. Very true that my statement not always true. I'm still developing my vehicle knowledge. But out of curiosity could the notorious gas cap issue possibly have any way of causing the issue or affecting something else kind of one thing leads to another type of thing.

 

Leak at gas cap o-ring seal us6uall is evap small leak, unless you totally leave the cap off in which case you'll get an EVAP largel leak code the number of which is somewhere in the vicinity of p0455.

Sometimes the ring is just shot and doesn't seal, sometimes there is a thin layer of corrosion so to speak that builds up on the mating surface to which the o-ring seals. I have used very very high grade Emory to wear that off without taking any metal with it period if you do get into the metal it will never seal right. So take your time. Usually the best fitting gas caps are the OEM ones so bite the bullet the first time, put out for the good gas cap. It should seal properly and if that does not solve your problem you can rule that out.