My daughters mustang chuggs and puffs black smoke when i am filling up the fuel tank...It runs fine otherwise runs out fine...but as soon as you start pumping fuel...if the car is running it will chugg then puff a lil black/grey smoke.
i have to run the car to fill it...if you shut off engine..the filler neck backs up and the pump shuts off....
what area should i look at to fix this issue..? charcoal cannister? evoporative system?

it does have a slight high idle between shifts...in other words it doesnt lower or drop off in the time it takes to shift gears..(manual 3.8)..its annoying to someone who is used to driving a stick...like myself.. and since i fit the repair bills...its surely taking away clutch life..as it slips the clutch since the rpms dont match the gear selected on up shifts...
but i digress...
Anyone have any clue how to go about diagnosing this?

02 3.8 v6 5spd.

 

Ouch keeping it running while fueling that's taking quite the risk there. I would take that thing in to find the problem.

Black smoke could be anything from not being properly tuned. Which could mean it's getting excess fuel in the cylinder heads that it can't burn off correctly.

Also take a look at the oil dipstick and see if the oil has a chocolate milk look to it if it does its getting contaminated.

 

no runs ok or no smoke when running or driving this issue must be in the evac or recirculation system in the tank?
like maybe a clogged return line or something..but like i say...it wont fill when engine off..it will only let me put 1 gallon in then it runs up the filler and kicks the automatic off the gas pump.....no matter what speed i pump..or attempt i try to make...
it will only take on fuel if the car is running..
and as soon as i start pumping...you can see .feel and hear the car begin to chugg then black sooty exhaust starts...

again other than the high idle or slow idle return..it runs fine...