clickman

I'm having the all-too-common problem of the tank not filling to the top. Constant clicking off of the pump nozzle. Filling the tank with the fuel handle at every angle of 360 degrees didn't work. Pushing the little tab that's normally depressed by the cap didn't work (although the tab is looking kinda worn). This has been going on for a few years, and I'd talked myself into thinking this is just a Porsche thing, but now I want it fixed. It did work, so there's something wrong. No CEL/MIL. No difficulty starting after filling.

After a ton of research, it finally sunk into my pea brain that there are two systems: the main Evaporative Emission Control System (EVAP) that captures stray fuel vapors while operating and sitting, and the intermingled Onboard Refueling Vapor Recovery system (ORVR). It's the ORVR that vents the tank during fueling.

Pushing the fueling nozzle into the filler hole moves a flap that activates a reed switch on the filler pipe. This switches operation from EVAP to ORVR, activating two valves:

- the ORVR valve on top of the fuel tank

- the "fresh air" valve located in the front right wheel arch

With those two valves open the tank can vent to atmosphere during fueling, through the carbon canister.

So why is mine not working?

Some people have a problem with Fuse E6, which powers the ORVR system (grounds out from a telephone connector in the center console). Mine is fine. So next is the two valves. I pulled off the wheel liner to get to the valve in the wheel arch. I can hear and feel it activating. Then I pulled out the battery and the lid under it, getting to the fuel tank. The ORVR valve there I could also feel activating.

Assuming the valves are actually doing something, that leaves the carbon canister and the interconnecting hoses/pipes. The atmospheric line from the fuel cap area seems like a potential culprit and it's subject to collecting debris. My question: how is the line disconnected from the valve plenum without damaging it? See pic

Assuming the lines aren't plugged, and the carbon canister is plugged, wouldn't this set off a CEL/MIL? It is part of the EVAP system as well.

Then there are a couple of potential mechanical issues not related to ORVR air flow. The spitback valve at the end of the filler tube could be sticking or blocked. But woudn't the tank be difficult to fill in its entirety, rather than just near the top? Then there is the issue with the flexible fuel hoses inside tank obstructing the spitback valve. Porsche issued a TSB: Fuel Tank Hose Modification 5/99 2015 or 03/99 2015 (different numbers from different forums) - tie fuel tank hoses out of the way of filler pipe flap. I couldn't find the TSB. Is it applicable to cars past 1999? Does it make sense that like in my case it started about 15 years after the car hit the road? Can this be determined by putting a scope down the filler pipe or would the spitback valve get in the way? I did try this but got chicken and stopped when the scope got to a section of the pipe that looked corrugated.

So my questions, for those of you kind enough to help:

1. How is the pipeline disconnected from the valve plenum without damaging it?

2. Wouldn't a plugged carbon canister set off a CEL/MIL?

3. Does anyone have the TSB? What years is it applicable to? Can this happen many years after the car is sold?

4. Have I missed anything as far as potential failure mechanisms or is there any other advice?

Thanks!

2001 base, manual

zoomster1776

Thanks for doing all this research. I have the same prob (2000S) but have learned to live with it over the years but today I am taking it to an indy shop and have asked them to look at it. I will keep you posted. I do wonder how much I am willing to spend on this 'problem'.

clickman

Thanks. Yes please let me know how it goes for you.

swmic

My 02 Base track car also has this issue. I get around it by turning on the ignition when fueling. Discovered it by accident.

zoomster1776

interesting. but this does not work for me. tried it multip0le times. This problem is more complicated than I thought.

zoomster1776

"...the ORVR valve on top of the fuel tank...". They (the indy shop) simply 'cleaned' this item. car fills just fine now. and as always YMMV. btw, ti cost me 200$ so you could DIY. The shop also said that someday the ORVR may have to be replaced if the old prob resurrects itself. Interestingly, the indy folks did not seem the least bit surprised by the problem or the fix

clickman

Zoomster: Excellent info. Thanks for closing the loop. It didn't seem to me that getting that valve out (sitting on gas tank tucked under the metal access port edge) would be that easy. Might be beyond me to get it out and clean it.

I had to fill up the other day so I tried the upside down fueling and it seemed to work pretty well (this time). For fun I also held a small piece of tissue paper near the vent exit, and it did blow aside while I was fueling. So there was at least some air flow! Which means that both valves are open to some degree. But could maybe stand the cleaning you refer to.

ZuffenZeus

I've had this problem on my last 996 and it was a fuel vent. Got some good advice from a master tech. Simply told me to NEVER over fill these cars with gasoline by clicking over and over again. When it clicks off, don't keep pushing gas in it. Well, when I bought the 996, I couldn't even go 30 seconds and the pump would click off. So the advice I received was to try to slowly put gas in the car with the fuel pump nozzle NOT inserted all the way. This would allow more air to escape from the tank. It worked! Was able to fill the tank up. However, if I pushed the fuel in the tank a full speed, it would still click off over and over again. However, over the period of 6 months of doing this simple procedure, the vent/canister corrected itself and was able to accept gasoline a lot faster. I guess the 996 was subjected to years of bad fueling practices?

Now, my daughter's car was experiencing the SAME problem. She has a Volvo XC60. After a while, the car displayed a CEL. I scanned it and the DTC pointed to the charcoal canister. I removed the Bosch charcoal canister and it was saturated in fuel. I replaced it with a new OEM part and the problem was solved. I guess the moral of this story is don't keep pushing fuel in the tank when it's completely full. When it clicks off... STOP.

As a side comment... I found out that all of my family was doing this poor practice of over clicking fuel into their cars. Why? I suppose because the cost of fuel, they were trying to get the most for their money. They'd use a one-time discount that gave them .25 -.50 cent off per gallon. Therefore, in their minds, they wanted to get the most for their money.

Same thing goes for using cheap gasoline. They think they're saving money but in the long term, they're hurting the engine. I'm a poster child for this... my wife use to run Kroger or Ingles gasoline all the time with her new Tahoe with DFI. She clogged all the injectors. Thankfully the two fuel pumps survived. She did it again with her XC90 and started getting a CEL. Traced the DTC and it was point to fuel. Started putting Shell V Power in it and the CEL went away and hasn't been back.

Learn from me people!!!

clickman

Thanks for your thoughts on refueling procedure. I have tried going slower once it gets past the initial full-flow click-off, which didn't help. I'll give it a shot at doing the entire refuel more slowly.
What fuel vent are you referring to?

tcora

The R&R operation seems pretty straightforward.

ZuffenZeus

On the 996 it was the vent (or bleeder) valve. #12 in the diagram.