i sometimes fill my truck up while running and when i do i notice when i let the pump run for w while then stop it ( to hit the desired price) the motor drops in idle, or when i am filling up and over fill it, it bogs down and soemtimes stalls, why is that,

 

I would think because you have the gas cap off

 

Mine is really weird with this.

I can't even run it w/o the gas cap...I think my fuel pump is going bad.

I used to fill it up with the truck running all the time...no problem. Then one time I went to fill it up like that and took out the gas cap and it just stalled. I to this day can not fill it up while running. Weird

 

Your not supposed to fill while running, it starts to throw codes, not to sure about acting funny but i know a guy that did this with his new f350 and it threw up 33 different codes.

 

well it doesn't throw codes with mine, never has, but I have always filled all my vehicles while running...atv's, dirtbikes, lawn mowers, trucks, cars, etc.

 

me 2, is it a suction thing??

 

Maybe the vent for the tank gets covered or something while at the fullest the tank can be. Get a vapor lock going on and the fuel pump can't pump the fuel, thus causing an odd dip in idle. but idk...

 

sounds right

 

well i filled my truck right up (while shut off) and it started and i got on my way then my tac dropped and it almost died, told my dad and he said his f150 does the same thing when filled right up.

 

Not a good idea, due to evap reasons and static electricity would be my answer. Why would you leave your vehicle running while filling up? You're getting 0MPG while sitting there filling up, if it's because you just like to watch your gas gauge then just leave the ignition in the "ON" position and it'll work exactly the same as having the engine running. BTW, Has anybody ever heard of the horror stories of static electricity causing fires at the pump? Do a google search if you need more convincing.

 

Why fill up with the truck running? Your truck is off for a max of 5 minutes, if that, and the air temp on the inside won't drop that drastically.

Like BJ said, if it's for the gauge, just leave the key on, but turn the truck off. Or better yet, why not just wait until you get in the truck to find out how much gas you have?

 

you guys are even in FL, its not cold down there, I see no reason to leave it running when filling up, its a waste.

I never have and never will, diesel, gas, etc...

 

9 times out of 10 i leave my truck running and it doesn't phase it.

 

Its the opposite...it's hot out. I always used to fill while running, I stopped doing it after my truck wouldn't stay running...now I'm against it after I saw a few videos...sucks it took that for me to realize it though

 

i do it just to do it, not really a big deal, i was just wondering y it did that, hell i would like to fill up my truck running, b4 filling my truck up while the azz hole next to me is smoking while he fills up

 

I don't see the point either, you can run the AC with the truck off.

 

Yes and he'll be the one getting the heat for doing so if it were to start a fire. Why 'add to the fire', to sort of speak?

To answer your question, research your truck's evap system, i'm willing to bet it has something to do with why you are experiencing what you are.

 

What? No. The truck has to be on to turn the compressor.

 

Leaving the truck running is not a fire hazard. Some people seem to have evap system problems but other than that, there is no danger in leaving it running. Cell phones aren't a fire hazard either despite what the internet says.

Static electricity from getting in and out of the car and fueling cans in the trunk or on plastic bed liners is a real fire hazard. That's about it. Oh, smoking too. That's not a good idea either.

 

that is a lame excuse. go to another station!

 

I said it wrong, I'm too busy, you can still keep air circulating, its not like your trucks going to get hot again sitting there for 2 min as you fill up.

 

I agree, its not gonna get hot. Ignition on, it is fan only.

 

As pretty much everyone else in this thread mentioned why would you leave the truck on while fueling up..

 

When i was selling cars we had a few trucks on the lot that had dead batteries and were running on fumes. We would jump them and drive to the gas station. But the batteries didn't recharge enough to start the car back up so we would leave them running when we put in a few gallons of gas. But aside form this situation I see no need to leave your vehicle running.

 

The Vapor Management Valve is attempting to purge the canister using engine vacuum. When you leave the fuel cap off during purge, it effectively creates a large vacuum leak that can cause a rough idle or stall.

Every gasoline pump has a sign that tells you to turn off the engine while refueling. So does your owners manual.