Diagnosing P0089. Low fuel pressure when OFF?

[funditor]

Hi guys,

2006 XC70 here. P0089 comes on about 30 miles after CEL reset - Fuel Pressure Regulator (performance). The vehicle runs great. It might turn over just a touch slow, but is almost instant. The light usually comes on while idling.

1. I had a spare fuel pressure sensor (that goes into the end of the rail on the engine) from a previous XC70. Swapped it out. Code still comes on.
2. I notice that when I depress the Schrader valve on the fuel rail on the engine when it is OFF, a bit of gas just comes out without much pressure. When I depress the same schrader valve on a 2005 XC70 that's OFF (and been OFF for days), gas comes out with considerable pressure. It actually makes a mist. On the faulty 2006, there's not enough pressure to make the mist.

I've read that there's a check valve built into the pump. Perhaps that check valve has failed and is causing low pressure when OFF?

What do you think? Can I splice in a check-valve somewhere to restore pressure and eliminate P0089? I'm just trying to pass inspection as cheaply as possible.

The fuel filter looks to be original (171 k miles), so I can change that too, but I don't think that could cause low pressure at the engine.

Thanks!

[RickHaleParker]

I would go after the fuel filter first and sniff for fuel leaks.

ECM-2900 (P0089) Fuel pressure Faulty signal .

Diagnostic trouble code (DTC) information ECM-2900

R2302980 Condition
The engine control module (ECM) controls the fuel pressure via the fuel pump (FP) control module using a pulse width modulation (PWM) signal. The fuel pump (FP) control module then controls the fuel pump (FP) depending on the pressure requested by the engine control module (ECM). The diagnostic trouble code (DTC) is stored if the control capacity of the engine control module (ECM) for fuel pressure reaches the highest or lowest value and the desired fuel pressure (target value) is not achieved.

The diagnostic trouble code (DTC) can be diagnosed when the engine is running.
For information about fuel pressure regulation, see VIDA Design and Function.

Substitute value
None.

Possible source

• Leakage in the fuel lines
  Blocked fuel filter.
  Dirt, debris, or loose objects in the fuel tank.
  Damaged fuel pressure sensor
  Damaged fuel pump
  Damaged fuel pump control module.

Fault symptom

• 1Q, Driving/Poor performance/lacks power/At take off
  7A, Starting/Engine stalls
  AA, Starting/Engine does not start/Engine turns
  AJ, Driving/Poor performance/lacks power
  AK, Driving/Hesitates/surges/Unsure when/at all times
  AL, Driving/Hesitates/surges/During acceleration
  AM, Driving/Hesitates/surges/During deceleration
  BB, Driving/Engine stalls/Unsure when/at all times
  BV, Driving/Hesitates/surges/At steady speed
  DL, Warning lights and chimes/Malfunction Indicator Light ("Check engine" light) indication/no indication

[abscate]

Replace fuel filter

Source fuel pump, but measure fuel pressure to spec after fuel filter replacement. Borrow gauge from Autozone in a budget

[funditor]

Thank you both. I actually did just that before seeing your posts:

All units in PSI
BEFORE:
Start: 54
Idle: 42
Off: 40
Off + 1'42": 24
Off + 3'05": 18
Off + 6': 12

Replaced fuel filter. Maybe old one had pin hole in it or something else due to rust causing pressure leak. Pressure test after:

Start: 54
Idle: 42
Off: 42
Off + 5 minutes: 34

Check engine light went off instantly.

[abscate]

I think it is supposed to hold something like 26 psi for 20 minutes but whatever.

Glad it’s done

[RickHaleParker]

2006 XC70 Fuel line pressure
Desired value
Relative pressure 380 kPa (55.114 PSI)
Absolute pressure 480 kPa (69.618 PSI)

[RickHaleParker]

think it is supposed to hold something like 26 psi for 20 minutes but whatever.

No less the 29 psi, 20 minutes after switching off.