Car's sputtering (very strange problem)
 

So real quick i have a 04 cayenne v6 with 77k on it.

On tuesday i picked up my car from the body shop from getting the bottom lips painted. there was between a quarter tank of gas and empty. so i went ti get gas and i filled it up with the car running (i was in a hurry). i believe i pressed 93 octane but to this day i still am not 100% sure. so put gas in and get in my car and the cars off. i start it up again and then the car starts sputtering idling up and down and dies out again. luckily i live right down the street from the station the basically coasted home. the car just kept dieing out. i would start it and it would go right away then start bogging out. so i thought maybe i put bad gas in it so i got some octane booster and put it in. that helped a little bit but not too much. so my cousin who is a mechanic comes over and says let me try this. so as the car is on and sputtering barley running he gets down and hits the gas take with his hand a couple times. all of a sudden the idle goes back to normal. CRAZY! so i drive it around and it was perfect again. this morning the same thing was happening so i hit the gas tank a couple times and boom idle went back to normal and i was good to go to work lol

Whats your guys opinions?

fuel filter?

fuel pump?

bad gas in the tank still?

fuel pump

might be a stupid question but is there 2 fuel pumps?

From previous threads it does look like a few fuel pumps have been replaced -- So it surly could be that -- and hitting the tank is an interesting

But I will tell you that my 06 CS will sputter if I leave it running while fueling. When first purchased -- I was filling it up running and it started to sputter like crazy and I turned it off. I did not make the connection until it happened again.

I do not know the why this happens -- maybe air getting into the fuel system?

Before I put a new pump in it I would drive it a bit.

To those more knowledgeable:
What do you think hitting the tank accomplishes -- Do pumps partially fail? I would understand it if the car would not start at all and hitting the pump got it going.

Can the pumps get air in them?

If you fuel the vehicle while running, I would expect a CEL.

Check valve

I would guess that this is your problem too but weird you had no CEL. Fuel system is pressurized and that includes the gas cap making an air tight seal. I had this problem with my audi several times if I didn't close the gas cap tight enough. It should self correct though after several key cycles.

I fuel with the engine running a lot in winter, never had a problem until the check valve went, it keeps the fuel system primed and pressurized while you fill up, if the problem changes how the car starts after fueling then its the check valve on the engine, $42 part and an hour diy

It was my understanding that the gas tank had to have multiple cycles to trip the CEL. On a couple of my cars this longer cycle trips a warning to check the cap - no CEL. Never had a CEL filling a running car.

I never got a CEL with the check valve BUT while driving if the fuel cap seal is broken then you will get a CEL on almost all German cars

My Mercedes flashes the fuel reserve warning light on the fuel indicator. My Jaguar has a pixel display for the warnings and will tell you to "check the gas cap".

We fill up in New Jersey all the time -- cheap gas and no self serve - but the kids pumping don't always put the caps on all the way. This happens on our Nissan all the time and that one will eventually trip the CEL - no pre warning

For the OP -- has he ever run regular in the V6. I always run premium in my CS so I can not comment on operation with regular. Some cars will not compensate all that well running regular gas -- although if it is running OK some times it sounds like it must be something else.

There is a recall on the high pressure fuel pumps in some models. You might want to check with the dealer. I just had mine done last week, and it smoothed out acceleration, especially on cold starts. Free factory repair, at least on my '08 CS, which is well out of warranty at 80k miles.