I work at a Volkswagen dealer and our owner has a 2008 Bentley Continental GT with the W12 engine. The vehicle has a slight misfire at idle and sets misfire DTCs for mostly cylinders 1 and 2 but has set codes for all bank 1 cylinders in the past. Using our scanner (telling it the car is an Audi with a W12) I can monitor fuel trim on both banks of the engine. Bank 2 is okay at close to 0% but bank 1 (master ecm address 01) is -15 to 20% at idle. I can unhook and plug off the big vacuum port on passenger rear side of the intake and my fuel trim values come back to normal and idle smooths out. I also tried swapping mass air flow sensors from side to side with no difference. Does anyone know what all the passenger side vacuum line goes to? I tried pinching the vacuum line to the fuel pressure regulator in case it was leaking fuel with no difference. Tomorrow planning on unhooking the EVAP system to see if possibly something is allowing fuel to enter the vacuum lines. Also planning on smoking the boost system on the passenger side to check for leaks. Am I missing anything? Does anyone know what all the passenger side vacuum hose hooks to? Oh BTW the engine was removed and the vacuum pipes were replaced at a shop in Vegas. Appreciate any advice!

 

Does anyone know what all the passenger side vacuum hose hooks to? [/QUOTE]


Hidden near the passenger side wheel well shield is a vacuum pressure sensor. This sensor's vacuum line junctions to the 13mm vacuum port on the passenger side rearword of the engine. The sensor branches to a black ridged plastic line going under the car towards the rear. That vacuum line controls the exhaust flaps and T's off to the evap canister. The evap canister is under the plastic rear undershield. Without much fuss one could pinch off the rubber vacuum line under the passenger wheel well at the sensor and see if the condition persists.

 

I found the hose you're speaking of. I pinched the hose off and the engine starts idling normally. I followed the line up the right fender and found that it went to the evap purge valve. I checked and the valve had a small leak (just like Volkswagens do!) I gained access under the coolant tank and found the part number of the valve. We happened to have it in stock! I replaced the valve and test drove again. When coming to a stop vehicle starts idling poorly again. I block off the line and vehicle idles normally. I traced the line to the rear of the vehicle to the charcoal canister. I've never monitored the evap vent filter while an engine was running but you can see gasoline fumes coming from the filter on the leak diagnosis pump. This seems odd to me but as I said I've never watched the evap vent while an engine was running. Any ideas?

 

I pulled the charcoal canister and it is full of gas.

 

Yes, was going to suggest checking the charcoal canister for fuel Ingress . Topping off the gas tank leads to that problem as you are aware of. Now explain that to the big guy.

Anyhow, that particular vacuum line is used to do periodic air tightness tests of the EVAP system. Indeed the Bentley is a over-sized Volkswagen.

 

Thanks for your help @1eapplebaum ! If I can ever return the favor please let me know!

 

Vwtech,
Glad it worked out. You're welcome, anytime.
E

 

Great call @1eapplebaum ,
Would the gas cap play any role in this malfunction, such as improper venting ?

Johnny

 

The gas cap missfitment would throw a large evaporative system leak trouble code.

The charcoal EVAP system has a vent tube inside the filler neck. Topping off the gas tank like we did back in the 70s forces petrol down this tube into the charcoal canister.

There is a warning on most modern vehicles including the Bentley [inside the gas cap cover flap] not to top off.

Thx Johnny

E

 

Thank you @1eapplebaum and @Vwtech ,

I had a similar problem this past Friday, I took the B for a ride and figured I would fill up at the Shell station, they just installed all new pump stations with advertising screens, pumps, hoses, and nozzles, I state this as I thought it was the cause of the issue while trying to fill up the tank, the attendant could not get it to fill at normal speed, as it kept clicking off, so I set it on the first notch which felt like it took 15 minutes or so to put 14.93 gallons in the tank, as it still kept clicking off at the first notch, and as in NJ we are not allowed to pump our own gas, the attendant wasn't to happy with me touching the nozzle, I even ask to move up to the next pump to see if that was the issue, but he didn't care or want to run my card again in the next station pump, so, because of the constant clicking off I am not sure if I over filled it, it did spit back a very small amount putting the first 5 - 8 gallons in, and he rotated the nozzle around the clock to try and find a sweet spot, but all positions behaved the same, and yes the engine/vehicle was shut down during the fuel filling.

I then drove the vehicle to the bank, and then back up to the garage were I have been completing my rebuild, I parked it for about 20 minutes and then decided to go for another quick ride around the area then park it for the night, well, 3 minutes into the ride I got tremendous backfires that sounded and felt like they were in the exhaust system right by my seat, when I pulled up to the driveway and let off the throttle it backfired about 6 more times, I scanned it to find misfires on cylinders 1-4, and a evap code that I can not remember at this moment, I cleared the codes and drove it out into the parking lot where are seamed fine, but I pulled it back in and called it a night, I will be scanning again tomorrow sometime.

What would be the cause of the lack of normal fuel filling time ?

Thank you for any thoughts.

Johnny

.

 

Johnny,

This situation reminds me of a Ford Explorer which the charcoal canister had been repeatedly contaminated by overfilling. Eventually the charcoal became a solid mass and would not allow the passage of pressure while refueling. The end result was painfully slow refueling.

However, there is a small possibility that the vent solenoid that is normally open to allow refueling is stuck closed. The only time this solenoid valve is closed is for a self check of the evaporative system's air tightness. The evaporative self check valve arrangement is where the vacuum line at the rear attaches to.

One possible way to confirm blockage ie. canister or solenoid valve is to remove the vent line from the purge valve next time refueling.

A third scenario is the purge valve which is near the engine compartment on the Rt side is defective allowing fuel vapors into the intake manifold while refueling. This too can cause backfiring and/or difficulty restarting the engine. However the purge valve would not affect refueling time.

JH,
Your rebuild project is looking good!!

 

Haven't checked the Bentley fuel fill neck, but I've seen other cars with a rollover valves inside the fuel fill neck that gets stuck closed if the vehicle has been sitting for some time. When you fill the tank the fuel backs up into the EVAP system vent and causes misfire / backfiring. A bad or loose fuel cap will cause CEL codes due to the failure of the EVAP pulling vacuum on the system indicating a leak.

So I'm guessing if you have a check valve or rollover valve in the fuel neck that would cause these issues.

 

I know this is an old thread but I think I've got exactly the same issue on my 2012 Continental GT...

What was the resolution? Did you replace the canister or were you able to empty it?

 

He replaced it. Once contaminated the charcoal element is impermeable.

 

OK that's great to know; thanks!