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Discussion Starter #1
Hey guys, I have a 2009 c5500 throwing a P0087 on a hard pull. Replaced the fuel filter, changed the fuel plug, and added a lift pump. Then replaced the Cp3, a set of 8 injectors, and replaced the rail pressure sensor. Still codes up and falls on its face under load. What am I overlooking? Thanks
 

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Remember that your FPR needs to have a sound electronic circuit. test to make sure you have 5Von the ref line, and no shorts, opens, or high resistance anywhere in the circuit.


DTC P0087 or P0088

Diagnostic Instructions



  • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
  • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
  • Diagnostic Procedure Instructions provides an overview of each diagnostic category.
DTC Descriptors

DTC P0087


  • Fuel Rail Pressure (FRP) Too Low
DTC P0088


  • Fuel Rail Pressure (FRP) Too High
Diagnostic Fault Information







Circuit/System Description

The fuel injection pump supplies high pressure fuel to the fuel injection rails, and then to the fuel injectors through high pressure pipes. The fuel rail pressure (FRP) sensor is a three wire sensor mounted in the right fuel injection rail. The FRP sensor uses a 5-volt reference circuit, a signal circuit, and a low reference circuit to monitor fuel rail pressure. This information is sent to the engine control module (ECM) to assist in the fueling of the engine.

Conditions for Running the DTC

P0087

  • DTCs P0090, P0192, P0193 are not set.
  • The engine is running.
P0088


  • DTCs P0087, P0192, P0193 are not set.
  • The engine is running.
Conditions for Setting the DTC

P0087


  • The actual FRP is more than 15 MPa (2,176 psi) below the desired FRP. OR
  • The actual FRP is less than 22.5 MPa (3,263 psi).
P0088


  • The actual FRP is more than 20 MPa (2,900 psi) above the desired FRP. OR
  • The actual FRP is more than 189 MPa (27,412 psi).
Action Taken When the DTC Sets



  • DTCs P0087 and P0088 are Type A DTCs.
  • The ECM commands the engine to operate in the Reduced Engine Power mode.
  • The message center displays Reduced Engine Power.
Conditions for Clearing the MIL/DTC

DTCs P0087 and P0088 are Type A DTCs.

Diagnostic Aids

P0087


  • Water or gasoline contamination of the fuel may cause this DTC to intermittently set. Refer to Contaminants-in-Fuel Diagnosis.
  • When ambient temperatures are below 0°C (32°F), the fuel tank pickup screen may be iced over from water in the fuel tank.
  • When power enhancing devices have been attached to the fuel rail pressure sensor circuits, this DTC may set and adversely affect the fuel system components.
  • If the fuel pressure relief valve is not torqued correctly, the valve will leak fuel into the fuel return system causing this DTC to set. The fuel pressure relief valve uses a bite type seal, and proper torque is essential for valve to rail sealing. Refer to Fastener Tightening Specifications.
  • High fuel injector return flow may cause this DTC to set.
  • The addition of fuel system enhancements, such as auxiliary fuel tanks or add on fuel filters may relate to driveability complaints.
P0088


  • This DTC will set if the electric fuel prime pump runs continuously during engine operation (van only). Refer to Fuel Pump Electrical Circuit Diagnosis.
  • If the fuel system pressure is actually too high, a fuel knock will exist.
  • A sticking FRP regulator may cause this DTC to set.
Special Tools

CH-48027 Digital Pressure Gage

Circuit/System Verification



  1. With engine running, observe the Actual Fuel Rail Pressure parameter with a scan tool. A normal reading would be approximately 40 MPa (5,802 psi) with the engine cold, and 30 MPa (4,351 psi) at operating temperature.
  2. Engine running, observe the DTC information with a scan tool. DTCs P0087 or P0088 should not set.
  3. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
Circuit/System Testing

P0087


  1. If DTC P0090, P0168 or P0191 is also set, refer to Diagnostic Trouble Code (DTC) List - Vehicle.
  2. Ignition ON for 90 seconds, verify the scan tool FRP Regulator Command parameter is less than 20 percent.
    • If greater than the specified range, replace the ECM.
  1. Attempt to start the engine.
    • If the engine does not start, refer to Engine Cranks but Does Not Run.
  1. Install the CH-48027 to the fuel rail service port and slowly increase the engine speed until reaching wide open throttle (WOT).
    • If more than 5 inches Hg of vacuum was present during engine speed increase, replace the fuel filter and inspect the fuel supply lines for damage between the fuel tank and the fuel injection pump.
    • If no restriction was found, test for high fuel return flow.
  1. With the engine idling or at an idle, command the fuel pressure control to 180 MPa (26,106 psi) with a scan tool. Observe the Actual Fuel Rail Pressure parameter. The actual fuel pressure should be the same as the commanded pressure.
    • If the Actual Fuel Rail Pressure is less than 165 MPa (23,931 psi), refer to Fuel System Diagnosis - High Pressure Side.
Important: If the fuel temperature is near 121°C (250°F) during the duplication of the complaint, or in the Failure Records for this DTC, inspect for a restriction in the fuel cooler air flow or the fuel heater always ON. Refer to Fuel Heater Always On.



  1. Operate the vehicle within the conditions for which the customer complaint occurs while observing the CH-48027. You may also operate the vehicle within the conditions that you observed in the Freeze Frame/Failure Records.
    • If the vacuum was more than 12 inches Hg of vacuum at any time in the operating range, inspect for kinked or restricted fuel supply lines.
  1. Operate the vehicle within the conditions for which the customer complaint occurred. Observe the Actual fuel Rail Pressure and Desired Fuel rail Pressure parameters with a scan tool. Fuel pressures should be the same for both parameters.
    • If the Actual Fuel Rail Pressure is less than the Desired Fuel Rail Pressure, refer to Fuel System Diagnosis - High Pressure Side.
    • If fuel system tests normal, refer to Diagnostic Aids.
 

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You fixed the fueling issue, validate your fuel system is 100% and then check your air flow and EGR systems. The demand for fuel is not with just the pressing of the pedal. My two cents: an air flow problem has a direct correlation to the fueling. See if you can map the fuel and air values and watch for the gaps.

I would also check the temps of the fuel and the condition of the cooler.
 

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Discussion Starter #4
Ok, we commanded pressure with the scan tool and jumped right up to max pressure. Another tech suggested possibly not getting enough volume, possibly a restriction in the tank. So I installed a Beans sump and new 1/2” line to the lift pump. Took it for a test drive. Ran good until the engine heated up. About 70mph it went into limp mode with same P0087. I commanded pressure again and could only get 17-18k. Power breaking it got to a little over 19.
Kinda sounds like a bump CP3 to me. If it were airflow or egr problems I could still command pressure, correct?
 
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