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Home >> Ford >> 1988 >> Cutaway 7.3 M >> Repair and Diagnosis >> Engine Performance >> System >> Fuel Injection System - Diesel >> Testing >> Engine Performance Diagnosis >> Diagnostic Procedure
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Diagnostic Procedure

  1. With engine running, check for coolant, fuel, oil, and air intake system leaks. If no leaks are detected, go to next step. If leaks are detected, service or replace faulty component(s). If problem persists, go to next step.
  2. Check exhaust system for dents or kinks which may cause restrictions. If okay, go to next step. If not okay, repair or replace exhaust system components. After repairs, go to next step.
  3. Install a piece of clear hose, in place of rubber hose, between fuel filter outlet and fuel return system. Start and run engine at idle for 2 minutes. Increase engine speed to 3000 RPM and check for bubbles in hose. Go to next step.
    NOTE: Correct direction of fuel flow is from fuel filter toward fuel return system. Fuel flow in opposite indicates restriction in fuel supply system. On dual tank vehicles, check fuel flow with tank selector in both positions for a minimum of 2 minutes.
  4. If fuel flow is correct and bubbles are less than 1/16" (1.6 mm) in diameter, go to next step. If fuel flow is correct, but bubbles are large in diameter, perform FUEL SYSTEM AIR LEAK DIAGNOSIS  and repeat step 3). If fuel flow is incorrect, go to step 12). Repeat step 3), when fuel flow direction is correct.
  5. Obtain a fuel sample and visually examine fuel (in a clear container) for dirt/rust particles, clouding, or water contamination. If okay, go to next step. If not okay, replace fuel filter. Clean and/or service fuel system as required. After repairs, go to next step.
  6. Using cetane tester included with Dynamic Timing Meter (Rotunda 078-00200), check cetane value of fuel sample. Cetane value must be more than 40. If okay, go to next step. If not okay, perform steps 7), 12), 13), and 16). Also tell owner to use higher rated fuel. DO NOT  replace injection pump because of low cetane value.
  7. Remove air bleed orifice hose from fuel filter fitting. Install Adapter (5651) and pressure test kit. See Figure. Start and run engine at 3000 RPM, without accessory load. Record pressure reading. On dual tank vehicles, check both tanks. If pressure is one psi (.07 kg/cm2 ), go to step 9). If not, go to next step.
  8. Remove vacuum purge valve from fuel filter adapter. Install Adapter (3019) and pressure test kit. See Figure. Make sure clamp is closed on fuel sample hose. Leave adapter from step 7) installed and cap end. Start and run engine at idle, without load. Record pressure reading. On dual tank vehicles, check both tanks. If pressure is at least 2 psi (.14 kg/cm2 ), replace fuel filter and repeat step 7). If not, go to next step.
  9. Position end of sample hose on Adapter (3019) in a clear, one-quart, graduated container. Follow instructions in step 8) and open sample hose for 30 seconds, allowing fuel to flow into container. Record volume. On dual tank vehicles, check both tanks.
  10. Volume should be at least one pint in 30 seconds. If both pressure and volume are okay, go to step 12). If pressure is okay, but volume is not, go to next step. If volume is okay, but pressure is not, replace fuel supply pump and repeat step 7). If both pressure and volume are incorrect, go to next step.
  11. Connect fuel return line removed in step 7). Install Adapter (5632) and pressure test kit to fuel supply pump inlet. With rear wheels off ground, start and run engine (without load) at 3300 RPM. Place transmission in "P" (auto. trans.) or Neutral (man. trans.). Record vacuum reading. On dual tank vehicles, check both tanks. Vacuum should be less than 6 in. Hg. If okay, go to step 7). If not okay, service or replace restricted fuel return line(s) and repeat step 7).
  12. Connect fuel return line removed in step 7). Remove fuel return line fitting (located on left rear of engine). Install Adapter (5663) and pressure test kit. Start and run engine (without load) at 3300 RPM with transmission in "P" or Neutral. Record pressure reading. On dual tank vehicles, check both tanks. Pressure should not exceed 2 psi (.14 kg/cm2 ). If okay, go to next step. If not okay, service or replace restricted fuel return line(s) and repeat this step.
  13. Remove cap on air cleaner test port and install Adapter (5650) and pressure test kit. See Figure. Start and run engine at 3300 RPM, without accessory load. Record restriction reading. Reading should not exceed 25 in. of water.
  14. If reading is more than 2 in. of water, but less than 25 in. of water, remove adapter. Install cap on air cleaner port and go to next step. If reading is more than 25 in. of water, replace filter element and check air intake system for blockage. After service, repeat this step. If reading is less than 2 in. of water, correct restriction on air cleaner test port and repeat this step.
  15. Remove screw from transfer pump pressure port cover. Install Adapter (T83T-9000-A) and "O" ring through cover and into port. Install Adapter (5850) and pressure test kit. Start and run engine (without load) at 3300 RPM with transmission in Neutral. Record pressure reading. If pressure is 90-110 psi (6.3-7.7 kg/cm2 )), go to next step. If not, replace injection pump. If problem persists, check and adjust dynamic timing. If problem continues, go to next step.
  16. With engine off, check that throttle lever contacts injection pump stop when accelerator pedal is fully depressed. If okay, go to next step. If not okay, adjust accelerator linkage. After adjustment, go to next step.
    NOTE: DO NOT  adjust position of full throttle stop screw. Tampering may cause injection pump damage.
  17. Start engine and bring to normal operating temperature. Check engine idle speed. See ADJUSTMENTS . If idle speed is correct, go to step 12). If not, adjust idle speed as necessary and then go to step 12).
  18. Start engine and bring to normal operating temperature. Check injection pump dynamic timing. See ADJUSTMENTS . Compare value to specification and correct for cetane value and altitude. If timing is correct, go to next step. If not, adjust timing. If problem persists, go to next step.
  19. Check injector inlet lines for kinks or restrictions and test injectors. See INJECTORS TEST . If lines and injectors are okay, go to next step. If not okay, replace damaged line(s) and clean or replace injector(s). If problem persists, go to next step.
  20. Remove crankcase depression regulator valve and plug opening to prevent blow-by. Remove oil fill cap and install Adapter (5631) and pressure test kit. See Figure. Ensure dipstick is seated in dipstick tube. Start and run engine (without load) at 3300 RPM with transmission in Neutral. Record pressure reading. Pressure should not exceed 6 in. of water. If reading is correct, replace injection pump. If not, problem is mechanical in nature.
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