I've been tracking down a fuel pressure problem with my '08 Cayenne 3.6 for about a week and have touched way more parts of this thing than I really wanted to now
Anyway, I had been having odd hesitation and stumbling issues off idle for a while and it finally got serious. It will idle and putt about just fine but any acceleration leads to heavy stumbling and while it will eventually get it to speed it's really undriveable.
I tossed my PORII on it and got code P2293 (fuel rail pressure). Running the live data stream the fuel pressure at idle is about 500psi but pulling away fro m idle gets up to maybe 800 psi then starts bouncing around between just 80psi and 800.
Through searching in a hurry I was convinced it was the high pressure fuel pump so I ordered one up and replaced it...no dice. Then I found some having the same issue with the low side pumps so I did the fuse pull trick and found it would not run at all on just the primary (drivers side) pump. So I ordered both low side pumps, in tank regulator and the filter. After replacing those still no change. I then decided all that was left is the high side pressure sensor and the pressure relief valve so I ordered both and installed the sensor but the valve is on a slow boat due late this week. In the interim I pulled the intake and inspected the injectors (looked fine but I replaced the teflon seals and all orings then reinstalled).
*I did find a broken actuator shaft on the vacuum operated varioram assembly so at least that wasn't a total waste.
So now here I sit waiting until Friday or Saturday for the part and I'm wondering if it would be bad form to mechanically block the relief valve just to test if that solves the problem. I'm not sure if the high pressure pump is internally (electrically) regulated or if it relies on this valve for normal operation on the high end. The risk would be over pressurizing the the high side and popping something like a fuel rail or injector.
The valve is a simple mechanical poppet that diverts pressure back into the low pressure supply line but I can't say for sure if it's part of the normal cycle.
Yea I know I basically threw parts at this rookie style but live and learn...anyway, here is the valve, thoughts? If not this what else could it be? Blockage in the low side pickups or lines? I'm running out of parts to replace
Thanks and apologies for the novel. Here's the valve (which I have removed, cleaned and inspected but it's not something you'd see the issue on unless it was an oring which it wasn't).
