Detroit Diesel Troubleshooting Diagrams

To determine if low compression is causing starting difficulty, perform the following steps: ‪

1. Perform a cylinder compression test.
2. Compare cylinder compression test results to specifications.
If cylinder pressure is below specifications.
If cylinder pressure is within specifications, call Detroit Diesel Technical Service Group.

Low Compression Repair

Perform the following steps for low compression repair: ‪

1. Remove cylinder head.
2. Inspect the cylinder head for worn or damaged valves.
3. Replace damaged valves.
4. Inspect the cylinder kit components for worn or damaged liners, refer to section ; pistons or piston rings;.
5. Verify repairs made to cylinder head valve(s) or cylinder kit components .

Test Engine with Repaired Cylinder Head Valve(s), and Cylinder Kit

Perform the following steps to determine if the cylinder head valve and cylinder kit repair resolved starting difficulty: ‪

Attempt to start and run the engine.

1. If the engine starts and runs, no further troubleshooting is required. Shut down the engine.
2. If the engine fails to start and run, call the Detroit Diesel Technical Service.

To determine if a restrictive air filter is causing starting difficulty, perform the following steps: ‪

1. Remove the air filter element; refer to OEM guidelines.
2. Attempt to start and run the engine.
   1. If the engine starts and runs, no further troubleshooting is required. Shut down the engine.
   2. If the engine fails to start and run.

Air Filter Replacement

Perform the following steps for air filter replacement: ‪

1. Visually inspect the air filter for clogging and replace as necessary; refer to OEM guidelines.
2. Visually inspect gaskets for deterioration and replace as necessary; refer to OEM guidelines.
3. Visually inspect air inlets for restrictions and clean as necessary; refer to OEM guidelines.
4. Verify air filter replacement.

Test Engine with Replaced Air Filter

Perform the following steps to determine if the replaced air filter resolved starting difficulty: ‪

Attempt to start and run the engine.

1. If the engine starts and runs, no further troubleshooting is required. Shut down the engine.
2. If the engine fails to start and run, check compression.

To determine if aerated fuel is causing starting difficulty, perform the following steps: ‪

1. Disconnect the fuel line return hose from the fitting located at the fuel tank; refer to OEM guidelines.
2. Place the opened end of the fuel line into a suitable container.
3. Start the engine.
4. Run the engine at 1000 r/min.
5. Visually check to see if air bubbles are rising to the surface of the fuel within the container.
   1. If air bubbles are present, repair is necessary.
   2. If air bubbles are not present, check for a restrictive air filter. Shut down the engine.

Aerated Fuel Resolution

Perform the following steps for aerated fuel resolution: ‪

1. Shut down engine.
2. Tighten all fuel line connections between fuel tank and fuel pump; refer to OEM guidelines.
3. Visually inspect all fuel lines between fuel tank and fuel pump for leaks.
4. Replace damaged components as required; refer to OEM guidelines.
5. Verify aerated fuel resolution.

Test Engine with Aerated Fuel Resolution

Perform the following steps to determine if aerated fuel resolution resolved starting difficulty: ‪

Attempt to start and run the engine.

• If the engine starts and runs, no further troubleshooting is required. Shut down the engine.
• If the engine fails to start and run, check for a restrictive air filter;

To determine if the fuel pump is causing starting difficulty, perform the following steps: ‪

1. Insert a piece of wire through the pump flange drain hole

2. Crank the engine momentarily and feel for wire vibration.

1. If the wire did not vibrate, determine if the drive hub or coupling should be replaced.
2. If the wire did vibrate, check for aerated fuel.

Drive Hubs and Coupling Replacement

Perform the following steps for drive hub or coupling replacement: ‪

1. Replace the drive hub or coupling.
2. Test the engine to determine if starting has been improved.

Engine Test with Replaced Drive Hubs or Replaced Coupling

Perform the following steps to determine if replaced drive hubs or coupling resolved starting difficulty: ‪

Attempt to start and run the engine.

1. If the engine starts and runs, no further troubleshooting is required. Shut down the engine.
2. If the engine fails to start and run, check for aerated fuel

To determine if a plugged fuel filters is causing starting difficulty, perform the following steps: ‪

1. Disconnect the fuel line return hose from the fitting located at the fuel tank.
2. Place the opened end of fuel line into a five gallon container.
3. Start the engine.
4. Run the engine at 1000 r/min.
5. Clock fuel rate for one minute.
6. Measure the amount of fuel flowed into the container.
   1. If the fuel flow is greater than 1 gal/min (3.8 L/min), check for air in fuel;
   2. If the fuel flow is less than 1 gal/min (3.8 L/min), replace the fuel filters;

Plugged Fuel Filter(s) Replacement

Perform the following steps to replace fuel filter(s): ‪

1. Replace the fuel filter;
2. Test the engine to determine if starting has been improved;

Test Engine with Replaced Fuel Filters

Perform the following steps to determine if the replaced fuel filters resolved starting difficulty

Attempt to start and run the engine.

1. If the engine starts and runs, no further troubleshooting is required. Shut down the engine.
2. If the engine fails to start and run, check the fuel pump;

To determine if the fuel supply valve is causing starting difficulty, perform the following steps: ‪

Check that fuel supply valve is open; refer to OEM guidelines.

1. If the fuel supply valve is open, check the fuel filters;
2. If the fuel supply valve is closed, repair is necessary;

Fuel Supply Valve Repair

Perform the following steps for fuel supply valve repair: ‪

1. Open the closed valve;
2. Prime the fuel system;
3. Verify fuel supply valve repair;

Test Engine with Fuel Supply Valve Open

Perform the following steps to determine if opening the fuel supply valve resolved starting difficulty: ‪

Attempt to start and run the engine.

1. If the engine starts and runs, no further troubleshooting is required. Shut down the engine.
2. If the engine fails to start and run, check the fuel filters;

To determine if low cranking speed is causing starting difficulty, perform the following steps: ‪

Install a tachometer to the engine and record engine revolution while cranking the engine; refer to OEM for guidelines.

1. If the cranking speed is greater than 100 r/min, check the fuel supply valve;
2. If the cranking speed is less than 100 r/min;

Low Cranking Speed Repair

Perform the following steps for low cranking speed repair: ‪

1. Drain the engine oil.
2. Remove oil filter(s).
3. Install new oil filter(s).
4. Refill the lubrication system with new oil.
5. Verify low cranking speed repair;

Test Engine with Replaced Oil

Perform the following steps to determine if the replaced oil resolved starting difficulty

Attempt to start and run the engine.

1. If the engine starts and runs, no further troubleshooting is required. Shut down the engine.
2. If the engine fails to start and run, check the fuel supply valve

1. Place the red lead of a voltmeter to the solenoid “BAT” terminal.

2. Place the black voltmeter lead to the starter ground terminal,

3. Engage the starter switch.

4. View the voltage reading on the meter.

1. If the voltage is less than specification while cranking the engine, replacement is necessary;
2. If the voltage is to specification while cranking the engine, check the cranking speed;

Starter Replacement

Perform the following steps for starter replacement: ‪

1. Replace the starter;
2. Verify replacement of starter;

Test Engine with Replaced Starter

Perform the following steps to determine if the replaced starter resolved starting difficulty: ‪

Attempt to start and run the engine.

1. If the engine starts and runs, no further troubleshooting is required. Shut down the engine.
2. If the engine fails to start and run, check the cranking speed;

To determine if a defective magnetic switch is causing starting difficulty: ‪

1. Start engine.
2. Clamp a heavy gauge battery jumper cable between the two large studs of the magnetic switch.

Basic Cranking Circuit

If the engine cranked with the jumper cable in place, the magnetic switch must be replaced;

If the engine did not crank with the jumper cable in place, check the starter;

Magnetic Switch Replacement

Perform the following steps for magnetic switch replacement: ‪

1. Replace the magnetic switch; refer to OEM guidelines.
2. Verify magnetic switch replacement;

Test Engine with Replaced Magnetic Switch

Perform the following steps to determine if the magnetic switch replacement resolved starting difficulty: ‪

1. Attempt to start and run the engine.
2. If the engine starts and runs, no further troubleshooting is required. Shut down the engine.
3. If the engine fails to start and run, check the starter;

To determine if corroded or damaged terminals is causing starting difficulty: ‪

1. Visually inspect terminals for corrosion or damage.
   1. If corrosion or damage are not found, check the magnetic switch.
   2. If corrosion or damage are found, repair is necessary.

Corroded or Damaged Battery Terminal Repair

Perform the following steps to repair corroded or damaged battery terminals: ‪

1. Repair or replace any corroded or damaged terminals; refer to OEM guidelines.
2. Verify repair of corroded or damaged terminals.

Test with Repaired Battery Terminals

Perform the following steps to determine if the repair resolved starting difficulty: ‪

1. Attempt to start and run the engine.
   1. If the engine starts and runs, no further troubleshooting is required. Shut down the engine.
   2. If the engine fails to start and run, check the magnetic switch.