• Scan tool is essential for proper diagnosis

• 1994-1995 models: OBD1 system

• 1996-2000 models: OBD2 system

• Diagnostic codes differ between year ranges

Potential Causes

• Low or no fuel supply pump pressure

• Dirty fuel filter

• Wastegate control solenoid malfunction

Root Causes

• Low or no fuel supply pump pressure

• Retarded timing

  • Use Tech 2 scan tool for TDC offset learn procedure

  • Typically set timing to -1 to -1.5 degrees

• Low engine compression

• Cracked pistons

Potential Triggers

• Dirty air filter

• Wastegate control solenoid failure or low vacuum

• Worn injectors (excess carbon on nozzle tips)

• Low fuel supply pump pressure

• Improperly seated EGR tower gasket

• Restricted exhaust system

  • Catalytic converter (soot trap) may be partially plugged

If you are having issues with difficult or no start when hot:

• Check minimum cranking speed with scan tool

  • Should be at least 200 rpm when hot, ideally more

• We recommend upgrading to our Powermaster starter on any truck, even if it doesn't have hot start issues

  • They blow stock starters away and increase cranking RPM to help with both cold and hot starts. While pulling less amperage at the same time.

• Check all grounds and upgrade with Quadstar battery cable kit to restore full starting system health

All diesel engines have more difficulty starting when hot because diesel fuel thins viscosity as the temperature increases. Older, more worn, injection pumps will start to show the issue even further. Increasing the cranking RPM is one way to resolve the problem before thinking about injection pump replacement.

Common Causes

• Worn injectors

• Overheating-related head gasket problems (typically on turbo side, cylinders #4 & #6 or 7 & 8 in the rear)

• Low engine compression

• Cracked pistons

• Receives fused 12-volt power when key is on

• PCM sends signal to close fuel control solenoid

• Fuel control solenoid sends closure signal back to PMD

• Closure signal response time called C-Time

Interpretation Guidelines

• Should vary slightly during acceleration/deceleration

• Fixed C-Time can indicate bad Fuel Control Solenoid

• Erratic C-Time at stable RPM suggests bad PMD

Replacement Criteria

• Intermittent dies with no codes

• Intermittent stalling with varying C-Time

• No start condition with specific C-Time readings

  • 1.95ms (94-95 models)

  • 0.01ms (96-2000 models)

Mounting Requirements

• Must be mounted to a "heat sink" or the Injection Pump

• Use new heat transfer pad

• Torque mounting screws to 23 LB-IN

• DO NOT reuse heat transfer pad

• DO NOT over-tighten mounting screws

Operational Characteristics

• Operates during cranking and after engine oil pressure rises

• Supply pressure: 5-7 psi at idle

• Test at fuel filter drain near coolant crossover

Zero Pressure Diagnosis

1. Remove fuel supply pump relay

2. Jump connectors #30 & #80

3. Check supply pressure

4. Likely cause of zero pressure: Bad oil pressure sending switch

Diagnostic Trouble Codes

• Can trigger DTCs:

  • P0370 (17)

  • P0251 (18)

• Caused by fuel aeration

• Fuel Leak from head and rotor weep hole

  • This can happen due to small piece of debris during assembly or just needing tightened again. There are 8 weep holes for the 8 delivery valves. These are the valves that the metal fuel injector lines connect to.

    • Tighten corresponding delivery valve

    • Remove, clean (compressed air and brake kleen), and torque delivery valve

      • Don't lose the spring and metal seal/washer

      • Torque to 50 ft/lb

• Must "see" through fuel inside pump

• Sensitive to:

  • Air in fuel system

  • Dirty fuel

  • Straight vegetable oil (SVO)

  • Low fuel supply pressure

  • Dyed fuel

  • Wiring issues

    • Loose pin tension at optic sensor plug

    • Degraded engine wiring harness

    • Ground issues

• Low resolution circuit: 8 windows

• High resolution circuit: 512 windows

• At idle, high-resolution circuit must read ~180,000 windows per minute

• For no-start condition: Disconnect encoder sensor

• Crank engine 15-20 seconds

• If engine starts, sensor is problematic

  • The computer can idle in "backup fuel mode" off the crank sensor only in this scenario. But it will not run with the optic connected due to signal errors, presumably.

Caution: Replacement requires partial injection pump disassembly and re-calibration

Vacuum and Operational Characteristics

• Controlled by vacuum

• 94-2000 turbo: No spring mechanism

• Vacuum check: Should maintain 20 inches Hg

Inspection Procedure

1. Remove inlet hose from compressor inlet

2. Verify turbo spins freely

3. Check compressor wheel for housing contact

4. Some side play normal due to oil-floating bearings

Discharge Considerations

• Normal to discharge oil from compressor housing

• Assess oil input vs. output

• Plugged air filter or bad CDR valve can cause excessive oil pullout

• Multiple codes can set from single fault

• Use Tech 2 scan tool to determine:

  • First triggered code

  • Triggering conditions

P0216 (Injection Pump Timing Control)

• Check stepper motor operation

• Verify injection pump timing

• Potential crank sensor issues

P0236 (Turbo Boost Performance)

• Check wastegate control solenoid

• Verify system vacuum levels

P0251 (Injection Pump Cam Sensor, Optic Sensor Low Resolution Track)

• Check for connector issues

• Investigate fuel contamination

P0335 (Crankshaft Position Reference)

• Diagnose crank sensor and wiring

P0370 (Timing Reference High Resolution System)

• Check for connector issues

• Check for fuel system contamination

Additional DTCs

• P1125: Accelerator Pedal Position Sensor

• P1216: Fuel Solenoid Response Time (Too Short)

• P1217: Fuel Solenoid Response Time (Too Long)

• P1218: Injection Pump Calibration Resistor Error

• P1214: Injection Pump Timing Offset Error

Wear Characteristics

• Typical lifespan: ~100,000 miles

• Critical indicators of replacement need:

  • Carbon buildup

  • Poor atomization

  • Degraded spray patterns

Connector and Electrical System Check

1. Perform visual/physical connector inspection

2. Disconnect and reconnect connectors

3. Use proper terminal test tool

4. Verify:

   • Proper connector engagement

   • Terminal condition

   • Contact integrity

• Verify year-specific diagnostic procedures

• Use appropriate diagnostic equipment

• Follow manufacturer troubleshooting guidelines

• Maintain systematic diagnostic approach

• Always check for multiple potential causes of a single symptom

• Use scan tool for precise diagnostic information

• Understand year-specific system variations

• Prioritize thorough electrical system inspection

Pine Hollow Auto Diagnostics on YouTube has made some great videos to show how you can correctly troubleshoot the 6.5L EFI system and electronics: