Porsche may have pulled their campaign for WB 08. Might be worth calling PNA with your VIN and seeing if your VIN was part of the campaign the HPFP was swapped out.

Thank you for the lead. I called PNA and they had me contact my local Porsche Dealer/Service Center. They said that the HPFP was replaced before I bought the car at 13,000 miles (I bought it at 18,000). I had no record or knowledge of that! Separately, I did another test this am following the one suggested by Petza914 where I turned the key on all the way, then off, and this time only waited about 10 seconds before then attempting to start. Boy -it was an incredibly tough start and struggled to life and then stalled and then struggled to life and only stayed lit when I goosed the gas. From the ideas above, this seems to implicate the HPFP I think?

The reason I had you wait 15 minutes between attempts yesterday is that there is countdown timer for the fuel pump where it won't prime a second time within X amount of minutes of the first one, I based this information off my DFI 09 Cayenne and the Cayenne actually primes the fuel pump when you open the driver's side door, but it won't do it a second time for 10 or 15 minutes. Not knowing the trigger the 997.2 uses to prime the pump (door, key on, etc) I wanted to make sure we covered all the possibilities yesterday during that test. Cycling the key a 2nd time before you tried to start it today was no different than just starting it the first time because of the priming delay. Did it smell like raw fuel or a rich mixture again when it finally started - if so, and the car runs fine once you get it started, I'm still leaning toward leaking injectors more than the HPFP. You know there's also a low pressure fuel pump that feeds or supplies the HPFP and that could be a suspect also. If the HPFP doesn't have fuel to pump when you first turn the key, it could be because of an issue with the LPFP or the anti-drain back valve in that pump (if it has one), especially since your HPFP was already replaced once.

Have to say, this is a fun website and I feel like I've got access to the Oracles of Porsche! So when I cycled the electrical and alternator on this am for a few seconds, then off, but tried to start in 15 seconds and it struggled mightily (worst yet!), I didn't pick up any fuel smell during or after it started but once again, the car does seem to run fine once started. The low pressure pump would be a pleasant surprise now I've been looking at $900 HPFP parts costs and have learned from this site that it's a very labor intensive replacement.

My non-DFI GMC pickup is having this same problem, which is why I've become familiar with the circumstances and its the anti-drain back valve in my fuel pump that's not holding pressure when the car sits, but it runs perfectly once started and it's 18 years old so I'm not inclined to drop the fuel tank to replace the pump just because it's taking 2 short starting attempts to come to life each morning. If it were on of my Porsches having this same issue it would get fixed but the DD pickup what sits outside all the time doesn't get the same level of care.

Look into the LPFP.

Mr. Petza isn't the only Rennlister with cool information. For example, I discovered all on my own, that if stand next to the passenger door of your locked 911 with your key in left hand.... well just look down.... you will have left your wallet on the seat. Happens all the time.

Peace
Bruce in Philly

You may not know that was engineered into the design of the seat bottom to prevent you from losing your wallet in the bar and so the guy with the Porsche doesn't have to pick-up the check. Those Germans are something else.

Something to consider. get it diagnosed and if ut is the hpfp, get it replaced soonest. Why, you ask?

When the hpfp was replaced on my cayenne, part of the procedure is to pull the fuel rails and injectors to inspect for metal contamination due to the failing hpfp. As this was done under warranty, porsche got lucky. All was clean.

My car had the similar issues last winter. It end up being a battery issue.

Nope, it’s not the LPFP. If that were faulty there’s no way for the HPFP to be fed fuel and the engine would not run at all. Another feature on the 997.2 engine is that no excess fuel is returned to the tank. Fuel regulation is part of the HPFP.

The LPFP could be working fine when it's running, but when it's off, it's allowing fuel from the pressure side that's not supposed to go back through the pump to actually go back through the pump where the line between the LPFP and HPFP is losing its prime. This is essentially what's happening with my truck except I'm losing the prime to the motor instead of the prime to a second pump. I'm not saying the LPFP has completely failed, I'm saying it's possible that some component in it has failed that's allowing this loss of prime phenomenon to occur.

This makes a lot of sense to me and seems to fit the symptom where it restarts fine after a short sit, but takes 6-7 seconds after it sits all day or overnight (really takes >6 hours before it's too noticeable).

The one test I did that I don't understand if it helps corroborate this is when I cycled the key on all the way without depressing the clutch so the dash lit up, alternator came on, etc., then shut it all off for about 15 seconds, then tried to start it. This was the most decisive isolation of the problem and the engine struggled to fire for about 8-9 seconds, struggled to catch, stalled, then started. Just cycling everything on and off did something which magnified the problem dramatically.

If the problem is the seal on the LPFP is letting fuel leak back to the no-pressure side and it's losing its prime, would that be exacerbated by this test?

That should really have no effect. Try what you did again and see if it's repeatable or if it starts the way it has been - struggling, but not excessively struggling.

OMG... and I have been using the console shelf all these years, so I remember to take my wallet :banghead:

Cheers!

I had nearly the exact same symptoms, and progressive degradation, with my 997.2. It turned out the be the high pressure fuel pump. Had the pump replaced under the CPO warranty and the car was back to roaring to life with the first turn of the key. Good luck.