Need help diagnosing high pressure fuel pump issues

Tiny
HAMFIST
  • MEMBER
  • 2008 PORSCHE CAYENNE
  • 3.6L
  • V6
  • 4WD
  • AUTOMATIC
  • 119,000 MILES
Cayenne with VW VR6 3.6 direct injection. My first car with DI. I recently did the valve cover gasket and PCV membrane because of running lean and idle hunting. Had to disconnect lower fuel rail to remove manifold, what a process.

That was 2+ months ago.

Fast forward to last week. Getting raw fuel smell through vents on hot start and idling at lights.

Hesitation under load on highway at 2,500 RPMs, feels like a misfire or ignition cut, bump bump bump, downshifts, RPMs goes up to 3,000+ and no issues.

No check engine light, no codes. I feel like i'm losing about 10-15% of normal power at all times. No MPG loss.

Before I rip off that manifold again and replace to $300.00+ pump, how can I confirm the issue?

I have a Foxwell with Porsche software so I can watch pids.
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Tuesday, September 14th, 2021 AT 9:14 AM

7 Replies

Tiny
DANNY L
  • MEMBER
Hello, I'm Danny.

I've attached a picture below with the fuel pressure specification. You should verify this first. Does your Foxwell have the same capabilities as the PIWIS tester? Let us know and we'll go from there. I've attached the specification below. Hope this helps and thanks for using 2CarPros.
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Tuesday, September 14th, 2021 AT 12:50 PM
Tiny
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I just went through every menu, no fuel pressure reading on pids. Grrr

I did find fuel rail psi on my torque app. At cold start it was low, then 350psi at idle, average 550 PSI at 50 MPH, downshifts brought 800 PSI.
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Wednesday, September 15th, 2021 AT 4:43 AM
Tiny
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  • MEMBER
Tiny bit confusing though, when you go to graphing it adds a zero, so watching the graph for 40 minutes, it went from 5,500 to 8,000 on downshift, 3,500 at idle.

I don't know what to think, when it coughed, I saw no drop.
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Wednesday, September 15th, 2021 AT 5:52 AM
Tiny
BORISKOP
  • EXPERT
Hello,

Your vehicle has 2 fuel systems, a pre-supply system from 2 in tank fuel pumps which will supply a low pressure of around 5-5.5 bar. These are the values my colleague gave earlier.
The high pressure part of the fuel system is regulated by the high pressure fuel pump mounted at the right rear of the cylinder head. For the DFI system the fuel pressure ranges from around 40 bar at idle to around 120 bar under full load.

I would suggest to start by checking the actual supply pressure from the in tank fuel pumps. Connect a manual fuel gauge to the supply line and start the engine. Check that the pressure is at around 5-5.5 bar or 50-55 PSI. Please see attached picture below for the supply line location.

How to check the supply pressure, the below You-Tube is for a VW Tuareg V8. This also applies to your vehicle,

https://youtu.be/ZVBaH2jsPg4

Also see our instruction.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Looking at the values you provided the scan tool seems to give live data values for the high pressure side, using the rail pressure sensor. The readings are possibly on the low side as 3,500 PSI at idle is on the lower side. The fuel pressure increases when there is more load on the engine but 8,000 PSI seems too low, we should see more than 100-120 PSI. This could be caused by either the pre-supply side being low or the mechanical high pressure pump being faulty.

Please let us know how you get along.

Cheers, Boris
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Friday, September 17th, 2021 AT 2:17 AM
Tiny
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  • MEMBER
I started watching the misfire counters and cylinder 6 is all over the place. When I did the PCV, the coil in cylinder 6 was practically fused in there with some sorta pink powder (i'm guessing dried coolant) I dug it out, blasted it out with air, and changed the plug, after removing all the. Whatever it was. I then reassembled the coil and it ran fine since.

Now I have the random misfires on 6.

I'm thinking I have 2 separate issues. I have ordered new coils, a new hpfp and new seal kits for the lower 3 injectors that have to be removed when the manifold comes off. I have read that once disturbed they have a chance to leak.

I don't want to do this again.
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Friday, September 17th, 2021 AT 2:54 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Hi,

It has been a few days since we heard from you. Have you been able to make any progress? We're interested in knowing if the problem has been resolved.

Let me know.

Take care,

Joe
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Sunday, September 19th, 2021 AT 8:23 PM
Tiny
HAMFIST
  • MEMBER
I will be doing all the work this weekend, had to wait for parts and tools.
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Monday, September 20th, 2021 AT 8:29 AM

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