Maybe somebody has had the same issue and can point me in the right direction. I have a 2011 Porsche Panamera 3.6L.
I replace the original battery a year and a half ago with a DieHard AGM. I recently started noticing that the car was taking a little longer to start these last couple months. The car's lucky to be driven once or twice a week. One day after the car been sitting for a week or so, I went to start it and there was nothing. I charged the battery and got the car going. A few more days later and the car was almost dead again. I took the battery in to the auto parts store and had them test it and they claimed it was "within specs" and would not warranty it out. They also tested the charging system with their scan tool and said the car was charging and that there must be some other issue.
It's still taking taking longer to start, maybe 3 or 4 seconds and then sometimes it would run rough upon starting until I touch the gas and then it smooths out. Now I'm getting engine codes and reduced power. It would clear up if I turned the car off and restarted it, but now its doing this every time it starts.

Last week I took the car in for an alignment to a German Motorsports repair shop who primarily works on Porsche. I asked him what it would cost to scan and check for codes. He said $175 so I decided to buy my own scanner and scan myself. While I was there, I questioned him about the hpfp. After seeing how it was acting, he said he was almost certain that it needed the high pressure fuel pump replaced.

Purchased my scanner and scanning, it shows p1031 and p1026. I decided to go ahead and make the plunge. I replaced the high pressure fuel pump (hpfp) today. I used my code scanner to clear all the codes before starting. The car is still takes 3+ seconds to start, rough idle, check engine light, reduced power on dash and code p1026 is still showing up (I haven't seen the p1031 again....not yet).
What next LOL???

I know, I probably didn't follow all the correct protocols to correctly diagnose, but after the shop advised that they felt I needed one based on the symptoms and everything that I'm reading online, I figured that's what it would be.
Side note, I had to purchase the cam plug from Porsche before installing the new pump which was $80!
80 bucks for some stupid little piece of plastic grrrrrrrr!!! Porsche should be ashamed of themselves!

Anyways, does anybody have any recommendations? I was honestly thinking battery voltage related from the start, but I have not made any headway on getting the auto parts store to warranty out the battery. I'm reading that these cars are extremely sensitive the voltage changes. The car's been sitting for a week and the AGM is reading 11.4 volts at rest. When I start the car it's reading 13.5 due to the charging of the battery.
Not sure where to go from here. Any suggestions or recommendations would be greatly appreciated.

 

I decided to leave my tail lights on for a bit just to see how the battery reacts, and within 30-35 minutes, the voltage is now 6.17v.
I wouldn't think that the ignition on without air conditioner or accessories going and just LED tail lights, that the voltage would drop that much that quickly unless there was a battery issue. Anyone agree with me on that?

 

Warrantied out the battery which had what we believe to be a bad cell. New battery installed and the same issues. Cleared the code and when I start the car it's rough idle, reduce engine power, and the code is p1026. Anyone have any ideas?

 

P1026 is a fuel high pressure reading implausibility, which could be a sensor issue. Might make sense to try changing this out as well?

 

Thanks for suggestion. This is the pressure sensor under the intake correct?

 

Yes, on the fuel rail. Looks like the work is the same for the V6 and the V8, but it's in the stickied engine document under "WM 240919".

 

There is an O-ring on the HPFP and the pressure sensor that also may be loose or leaking. Replace those too.

 

I recently replaced the high-pressure fuel pump (HPFP) Car just turned 50k. The new HPFP came with a new O-ring seal, so I bbelieveI should be good there. However, I am still experiencing the same check engine light, reduced power, and no improvement in the car's performance. The initial codes before the new HPFP were P1031 and P1026, but now I only have the P1026 code. I am considering changing the fuel pressure sensor and O-ring to see if that resolves the problem. If not, I would appreciate any other suggestions you may have. I am trying to manage these repairs on my own, as a local shop quoted me $350+ just for diagnostics which they said they would connect to the cars fuel system, drive it for 30 minutes, and monitor the car and fuel flows to see if they could pinpoint the issues. Thank you for any other suggestions!

 

Old car. Throw parts at it.

O2 sensors
Fuel pressure sensor(s)
Cam position sensors
Spark plugs
Ignition coils

Is there a lift pump fuel filter in or near the tank? If yes replace it. Might require dropping the tank.

 

Based on the reply, I'm thinking that your not very familiar with the Panamera....

 

It’s an old car. Are you throwing parts at it?

Which part on the list above do you object to?

 

Sorry, I took it as you were suggesting I just start throwing parts at it....older car, yes...relatively low miles at 50k for '11....abused or excessive use, no. Car is wife's, who doesn't know that the accelerator can be pushed more than half way to the floor LOL
I would like to be able to isolate the issue so that
I'm not just throwing parts at it, but actually figuring out the problem. The hpfp was expensive enough....and it's replacement hasn't completely resolved my issues.
I was in hopes that someone had experienced the same symptoms/ codes / problems and had some recommendations and what fixed their situation.

 

Did yo try replacing the fuel sensor? Any update on what you did? Thanks.

 

My .02 cents and without direct evidence to support...

I believe the low pressure fuel pump (located under the rear passenger seat) are often the reason the HPFP fail. Why? At start up, the low pressure system is needed to provide head pressure to the HPFP, which then takes it from there. Once the LP system is compromised, the HP side suffers and pumps 'dry', which destroys internal vanes, creates cavitations, and other bad things. And yes, I've read many, many threads stating the "LP side reads proper pressure" - well, let's face it... any time a reading is taken it's merely a snapshot in time. Meaning, the LP pump could be failing during start up, then coming 'back to life' when actual data is being observed on a scan tool. And all this time, the HP is directly impacted and slowly degrading.

Here is what Rick (me) is doing... as a preventive measure, I am replacing the LP pump and filter (about $800 parts) on my '15 PTS with 60K miles. I am doing this with the hope my working theory is correct, thereby extending the life of the much more expensive HPFP. Will it work? No idea... but, my car is now pushing 700HP at the crank and it needs all the help it can get with fuel pressure - and any weak link in the system will have problems downstream and affect other parts. So, I am swapping out a 'perfectly good' LP system (which arguably is not as efficient as day 1), just like I replaced a 'perfectly good' PDCC reservoir because an internal non-serviceable filter. I believe these small actions, which I perform myself, will assist in prolonging issues. Both HPFP and PDCC (power both the power steering and hydraulic sway bars) pumps are several thousand each, so focusing on extending their mutual lives. Same with the PDK system - I replace the pan & fluid at 40K intervals... again, believe this sage advice to avoid a $20K plus replacement.

As noted, I perform my own maintenance and enjoy attending to the car. That said, I am also a realist and understand parts wear and parts fail. I also understand these cars are true performance cars and not your standard 'run of the mill' grocery getter. Thus, needs to be viewed through that same lens. When I worked at GE Aviation, understandably preventive maintenance and scheduled parts replacement was a given for obvious reasons. The observable condition of aircraft parts is irrelevant - they get changed at scheduled intervals. So... there are moments when we need to replace 'perfectly good' parts to extend longevity of others, while ruling out possible causes.

I will be changing my LPFP and filter next month, with the expectation of it being unremarkable... good part out, new part in. No drama...

 

@huskeric

Great practice to preemptively replace components.

Does the LP pump project require dropping the fuel tank? How does it come out?