When I shut off my truck around 20 to 30 secs later I get a loud bang. It sounds like someone is hitting the gas take with a hammer. Does anyone know what this mite be
Thanks Mike

 

It's the Prius owner you last ran over stuck up in the undercarriage...

Maybe the fuel tank pucking, like a 2 liter coke bottle does when you squeeze it out of shape and set it down then it pops (no pun intended)..back into shape...I think and I'm sure I'll get corrected here too..that the emissions system pulls a small vacuum or pressurizes the fuel system to check for leaks...this makes the fuel tank pucking sound you maybe hearing...But like I said..I maybe talking out my *** too...FSTOP..here's your chance...

 

LOUD BANG!!!!!! Damn and I thought you were referring to my date last weekend!

 

Actually, your idea could work, if the system is not working correctly, and in fact, it used to happen years ago when little red spiders plugged a vent hole in the canister.
As the vacuum from the fuel being pumped into the engine increases, a vent allows fresh air to enter to equalize the pressure. Now the PCM runs different tests to see if there is too much vacuum (checks for plugged lines, vents, etc.)or if there is not enough pressure (checks for hydrocarbon leaks to the atmosphere) if the tests don't pass the PCM should signal for the service engine soon light to come on.
if it is the tank, and it could be, there is something wrong with the electronics too.

To be honest, unless hearing it, it could be hard to figure it out. Sometimes, exhaust systems pop, but usually not in a loud bang.
I checked the bulletins and found nothing.

 

Hey....I know HER!!!!!