CP3 Pump Failure Symptoms And Common Rail Injector Problems

This is a one-stop symptom checker for issues related to common rail injectors and CP3 pumps.

High-Pressure Common Rail Basic Information and Function

PumpHigh pressure is built and then delivered by the pump to the fuel rail manifold. Afterwards it then flows through the injector lines and connector tubes to get to the injectors. The fuel pressure regulator or fuel control actuator in the high-pressure pump, controls rail pressure.

The injectors have a hollow check ball which holds that rail pressure until the fuel solenoid is actuated by the ECM. This allows the check ball to rise off it’s seat and prompts an injection to take place.

The system will not build enough rail pressure to start the engine if the injector connector tubes that sit in the injectors are leaking or if the check ball in the injector is leaking. Another issue might be the high-pressure limit valve.

It takes approximately 4000 PSI of rail pressure to start the engine. The fuel system contains high-pressure fuel up to 26,000 PSI. It is very important that you do not use your fingers to find leaks! High-pressure fuel entering your bloodstream may result in limb amputation or even loss of life.

Do You Have No Start Or a Hard Start?

Where there is a low fuel supply or none at all there should be 10 to 15 PSI to the high-pressure injection pump or the CP3 at idle.

Part 2You will need to monitor the rail pressure to be sure that during cranking you have over 4000 PSI. If it is not, a hard start could be caused by one, or even more, injectors. If you do not see smoke from the tailpipe after about 10 seconds of cranking it means there is no fuel getting into the cylinders.

If the injector high-pressure connector tube or feed tube is not seated in the injector, the issue is a bad tube or there is an improper torque set on the nut, which should be a final of 37 ft. lbs.

A high-pressure limit valve should not leak at idle or during cranking.

Verify the CP3 pump output volume. To see how fast the pressure of the rails can climb, you can cap off all of the injectors. To start, it will take approximately 4000 PSI rail pressure.

For a shorted fan clutch, unplug the fan and try starting it again. Possible codes are P0483 or P2509.

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Do You See Black Smoke?

  • Smoke may not be visible on DPF equipped trucks. The exhaust may need to be disconnected or a test pipe temporarily installed to diagnose smoking issues.
  • To see if the smoke disappears while idle, you can test cutting out a cylinder when using a scan tool.
  • Check for a dirty air filter, and clean or replace it if needed.
  • A high-pitched squeal beneath the load may be heard if there is boost leaks or exhaust leaks.
  • The VGT turbo sticking open or closed will cause black smoke.

Is there a Miss? A miss can be caused by several issues listed here:

  • An injector connector tube that is poor quality or unsuitable.
  • A missing or damaged chamber gasket.
  • Low compression.
  • Excessive valve lash.

Take note: The engine will shake or it may be perceived that it is a miss if there is a bad dual mass flywheel.

Can you hear Knocks?

There may be a surge at idle due to low or no fuel supply pump pressure to the high-pressure pump. Knocking can be heard if the actual versus desired are too far apart which may be a bad FCA or Fuel Control Actuator.

Do You Have Slow Deceleration?

If the engine hangs at a higher RPM or is slow to decelerate, it may be injector wear due to excessive return that is causing this problem, as that is normally the case. The injectors will need to be replaced.

Is there Blue/White Smoke at Idle When Cold?

Smoke may not be visible on DPF equipped trucks. The exhaust may need to be disconnected or a test pipe temporarily installed to diagnose smoking issues.

Conditionally on temperature and altitude, it would be normal if in less than a minute the smoke clears. Unburnt fuel that burns your eyes is known as blue white smoke. If there is high altitude, cold temperatures and a considerable amount of idle time, these all are an indication of cold combustion.

Bad Injectors

InjectorsTo check for a potential bad injector, check the nozzle tip for signs of leakage.

When it is cold, normal ambient temperatures should be displayed by the coolant, intake air, inlet air and battery temperatures.

· When cold, check the intake heater operation.
· Check rail pressure when the engine is off. It should be zero PSI, plus or minus 500 PSI.
· Look for low or no supply pressure, supply pump or fuel filter etc.
Excess particulates can be a factor during excessive idle time due to injector tips having a build up of carbon due to the cold. Recurring regeneration cycles, plugging and DPF restriction can happen because of this. More than 20% idle time is excessive.

Are You Encountering Dilution Issues?

Dilution can result from an upper injector O-ring that is bad or not sealing.

· Examine the system for a cracked injector.
· Check for a leak at the high-pressure pump drive shaft seal.

Is There a Problem With The Fuel Supply Pump?

All 6.7 Liter engines use an in-tank style supply pump like the later 5.9 Liter engines. FASS pumps are one of the options that are able to replace the in-tank supply pumps and are able to be mounted on the frame rail.

High-Pressure Injection Pump (CP3 Pump)

Injection PumpMost starting problems due to low pressure are caused by bad injectors as a result of erosion of the check ball seat. The pressure is supposed to default to a max of 26,107 PSI when you unplug the fuel control actuator. The pump cannot build an adequate amount of pressure if the injection system has a leak. The high-pressure pump will most likely need to be replaced if dirt and/or water has contaminated the pump. Generally, the injectors are afflicted first, however, contaminants also will go through the CP3 pump. To curtail injector cackle, the CP3 must be “phased” with these engines during installation. In the service information you can find a timing procedure.



Tom Zelinka has been an Alberta Journeyman Automotive Mechanic and Interprovincial Red Seal since 1978. In 1981 he then received his Alberta Journeyman Heavy Duty Mechanic Certificate and Interprovincial Red Seal. He has received Certificates for:  Cummins engine certification on N855/N14/M11 Engines, Cummins B/C/ ISB Series Engines, Cummins B/C/ISB Series Engine Fuel Systems, and Cummins B/C/ISB Series Electronic Engine Controls.

Interprovincial CFC/HCFC/HFC certification, Alberta Liquid Petroleum Gas Certification, Alberta Certified Advanced Mobile Hydraulics, Alberta Certified Diesel Engine Control Systems.

As the technology and models change, Tom continues to stay on top of the industry to be sure that you are receiving superior service for your Dodge Cummins diesel truck.