I have a 2014 Silverado, 5.3 liter. I have noticed twice, when I fill the truck up, then try to keep filling the tank up, topping it off, I will get a code on the charcoal canister system. The code will clear after several weeks of running. So now I do not fill it up full. the first click of the nozzle is all I do now. As for running rough, I have not had any problems.

 

The first click is only as full as you should be going, anyhow. All gas tanks are designed with extra space at the top to allow the EVAP system to work properly. The space needs to be there to allow for fuel and tank expansion/contraction with changes in temperature and pressure.

If you fill it beyond the first click, it reduces the space, which can cause problems such as:

1) CEL with codes for the EVAP system.

2) Allows liquid fuel to get into the charcoal canister which can break down/dissolve the charcoal depending on how long it’s exposed; eventually the charcoal can work it’s way into the engine via the purge valve. This would be the equivalent of sand and dust getting past the air filter.

3) Kill a fuel pump depending on how the system is set up, because instead of the tank venting properly, the vents are plugged and the fuel pump actually creates a vacuum in the tank as it runs. The pump then has to work harder to deliver the correct quantity of fuel.

4) If the above scenario doesn’t kill the pump first, it can cause the fuel tank to collapse and then kill the pump. I’ve seen this once on a work truck for an excavation company. This truck was just a job site tool truck and always caked in mud. They towed it to us because it wouldn’t start - I found the fuel pump wasn’t running and verified it had good power and ground. When I removed the tank shield, the bottom and sides of the tank were sucked inward. I found that not only was the fresh air inlet for the canister plugged, but so was the filler neck vent hose. The gas cap as well was full of dirt, so in effect, this tank was completely sealed. I ended up not only putting a tank, pump and all new EVAP components, but also flushed the filler neck hoses and purge line with water and compressed air to make sure it was all clean.

Granted, that was a worst case scenario, but it gives you an idea of how bad it can get.

If you’re someone who has to see an even dollar amount on the pump, only add enough to go up to the next dime or dollar.