Wont start after fueling

[GENNY429]

About 3 weeks ago, I stopped to get gas and filled up. Wouldn't start. Had to pump the gas pedal like an old carb to fire it up then rev it a few times. Then it was fine. Didnt do it again until next time I got gas. Now it does it every time I get gas, fill up or not. Has never ever done this outside of getting gas. I do have CEL with the code for evap solenoid, but that was on long before this problem. Any thoughts? 2012 non-RSpec 5.0 sedan.

 

[mikec]

I'd get that evap solenoid fixed first. Normally, such solenoids open when the engine is warmed up and running so intake manifold vacuum can draw gas fumes out of the charcoal canister. If your valve is stuck ON, or leaking when it should be OFF, then that is similar to a vacuum leak which makes started difficult for pretty much any car.

When you add gas, you are opening the fuel tank so any vacuum that accumulates in it, as fuel is drawn out by the engine, gets lost. Normally fuel tank vacuum builds up a bit, then the gas cap's spring-loaded valve opens for a moment to let fresh air in, reducing the vacuum. The computer monitors for this pressure cycling; when it doesn't see it you'll get OBD-II codes. When you open the gas cap and eliminate ALL vacuum in the tank, the leaking evap solenoid can let air from the fuel tank & charcoal canister (evaporative emissions system) parts into the engine, resulting in low vacuum at start-up. Basically, rather than drawing air through the air filter, throttle plates, etc. (i.e. the normal way) the engine is "breathing" through the evap canister. Once you've driven a bit, vacuum collects in the gas tank again so there is less air in there... the engine has to "suck air" through the normal path: air filter, throttle plates, etc. past the sensors that the computer uses to measure airflow.

I'd expect just opening the gas cap - without adding fuel - would cause the same symptoms. Try it as a test. If the car starts properly after opening the cap, then the bug is something else... like gas getting into the evaporative emissions control system flooding the engine. Holding the throttle wide-open helps because you're adding a lot more air this way. Over-filling the tank can let gas into places it's not supposed to be...

mike c.

 

[GENNY429]

I'd get that evap solenoid fixed first. Normally, such solenoids open when the engine is warmed up and running so intake manifold vacuum can draw gas fumes out of the charcoal canister. If your valve is stuck ON, or leaking when it should be OFF, then that is similar to a vacuum leak which makes started difficult for pretty much any car.

When you add gas, you are opening the fuel tank so any vacuum that accumulates in it, as fuel is drawn out by the engine, gets lost. Normally fuel tank vacuum builds up a bit, then the gas cap's spring-loaded valve opens for a moment to let fresh air in, reducing the vacuum. The computer monitors for this pressure cycling; when it doesn't see it you'll get OBD-II codes. When you open the gas cap and eliminate ALL vacuum in the tank, the leaking evap solenoid can let air from the fuel tank & charcoal canister (evaporative emissions system) parts into the engine, resulting in low vacuum at start-up. Basically, rather than drawing air through the air filter, throttle plates, etc. (i.e. the normal way) the engine is "breathing" through the evap canister. Once you've driven a bit, vacuum collects in the gas tank again so there is less air in there... the engine has to "suck air" through the normal path: air filter, throttle plates, etc. past the sensors that the computer uses to measure airflow.

I'd expect just opening the gas cap - without adding fuel - would cause the same symptoms. Try it as a test. If the car starts properly after opening the cap, then the bug is something else... like gas getting into the evaporative emissions control system flooding the engine. Holding the throttle wide-open helps because you're adding a lot more air this way. Over-filling the tank can let gas into places it's not supposed to be...

mike c.

On a waaaay stupider level, this is kind of what I thought. My thought was by opening the cap, I was reducing pressure in the tank, and thinking maybe my fuel filter was a little clogged, that this no pressure situation was causing not enough fuel to get through the filter. Youre answer was more than I was hoping for, so THANK YOU. I have actually removed the solenoid previously to see if banging on it would break it free to work, but no dice. It's in the trunk and is a bear to get at, cause after 20 bolts you have to get under the car and bend your wrist in really unnatural ways to get around the axle, but for $75 I can get the part and do it myself. Thanks again. I actually learned quite a lot about the evap system from your reply.

 

[GENNY429]

On a waaaay stupider level, this is kind of what I thought. My thought was by opening the cap, I was reducing pressure in the tank, and thinking maybe my fuel filter was a little clogged, that this no pressure situation was causing not enough fuel to get through the filter. Youre answer was more than I was hoping for, so THANK YOU. I have actually removed the solenoid previously to see if banging on it would break it free to work, but no dice. It's in the trunk and is a bear to get at, cause after 20 bolts you have to get under the car and bend your wrist in really unnatural ways to get around the axle, but for $75 I can get the part and do it myself. Thanks again. I actually learned quite a lot about the evap system from your reply.

you have to pull the whole canister system out and then take the solenoid off of the whole contraption. Your answer makes sense for another reason. I have an OBD reader that will clear codes until the computer cycles. When I first got the code, it would stay off for a while and then come back after a few cycles. Now it comes back almost immediately. So I am assuming that the solenoid "was failing" and now "has failed".