MBE 900 – Section 15.12 Rough Running or Stalling

Section 15.12
Rough Running or Stalling

There are several causes for rough running or stalling. These probable causes are:‪

• Low Battery Voltage
• Aerated Fuel
• Insufficient Fuel Flow

Section 15.12.1
Troubleshooting Procedure for Low Battery Voltage

To determine if a weak battery is causing rough running or stalling, perform the following steps:‪

PERSONAL INJURY ‪
To avoid injury before starting and running the engine, ensure the vehicle is parked on a level surface, parking brake is set, and the wheels are blocked. ‪

1. Start and run the engine.
2. Measure the battery voltage; refer to OEM guidelines.
   1. If the battery voltage is greater than or equal to 10.5 volts, check for aerated fuel; refer to "15.12.3 Troubleshooting Procedure for Aerated Fuel" .
   2. If the battery voltage is less than 10.5 volts, replace the battery; refer to "15.12.2 Battery Replacement" .

Section 15.12.2
Battery Replacement

Perform the following steps for battery replacement:‪

1. Remove and replace the battery; refer to OEM guidelines.
2. Verify battery replacement; refer to "15.12.2.1 Test Engine with Replaced Battery" .

Section 15.12.2.1
Test Engine with Replaced Battery

Perform the following steps to determine if the battery replacement resolved the concern:‪

PERSONAL INJURY ‪
To avoid injury before starting and running the engine, ensure the vehicle is parked on a level surface, parking brake is set, and the wheels are blocked. ‪

1. Start and run the engine.
2. Run the engine at idle with a no-load condition for approximately five minutes, allowing the engine coolant to reach normal operating range, 88-96°C (190-205°F).
   1. If the engine is not running rough or stalling, no further troubleshooting is required. Shut down the engine.
   2. If the engine is running rough or stalling, shut down the engine. Check for aerated fuel; refer to "15.12.3 Troubleshooting Procedure for Aerated Fuel" .

Section 15.12.3
Troubleshooting Procedure for Aerated Fuel

To determine if aerated fuel is causing rough running or stalling, perform the following steps:‪

1. Disconnect the fuel line return hose from the fitting at the fuel tank; refer to OEM guidelines.
2. Place the open end of the fuel line into a suitable container.

   PERSONAL INJURY ‪
   To avoid injury before starting and running the engine, ensure the vehicle is parked on a level surface, parking brake is set, and the wheels are blocked. ‪

3. Start and run the engine.
4. Operate the engine at 1000 rpm.
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, shut down the engine; refer to "15.12.4 Aerated Fuel Resolution" .
   2. If air bubbles are not present, shut down the engine. Check for high fuel temperature return, which would be an indication of insufficient fuel flow.

Section 15.12.4
Aerated Fuel Resolution

Perform the following steps to resolve aerated fuel:‪

1. Tighten all fuel line connections between fuel tank and fuel pump; refer to OEM guidelines.
2. Visually inspect all fuel lines for leaks between fuel tank and fuel pump.
3. Repair damaged components as required; refer to OEM guidelines.
4. Verify aerated fuel resolution; refer to "15.12.4.1 Test the Engine with Aerated Fuel Resolution" .

Section 15.12.4.1
Test the Engine with Aerated Fuel Resolution

Perform the following to determine if aerated fuel resolution has resolved rough running or stalling condition:‪

PERSONAL INJURY ‪
To avoid injury before starting and running the engine, ensure the vehicle is parked on a level surface, parking brake is set, and the wheels are blocked. ‪

1. Start and run the engine.
2. Run the engine at idle with a no-load condition for approximately five minutes, allowing the engine coolant to reach normal operating range.
3. Test for rough running condition.
   1. If the engine appears normal, no further troubleshooting is required. Shut down the engine.
   2. If the engine is still running rough, shut down the engine. Check for insufficient fuel flow. Refer to "15.12.5 Troubleshooting Procedure for Insufficient Fuel Flow" .

Section 15.12.5
Troubleshooting Procedure for Insufficient Fuel Flow

To determine if insufficient fuel flow is causing rough running or stalling, do the following steps:‪

1. Perform Fuel Flow Test #3 and measure the fuel return flow rate. Refer to and see Figure "Fuel Circuit Flow Diagram" .
2. Analyze the fuel flow test results.
   1. If the fuel rate is 0.9 L/min. (0.2 gal/min.) or more, no further troubleshooting is required. Contact Detroit Diesel Customer Support Center at 313-592-5800.
   2. If the fuel rate is less than 0.9 L/min. (0.2 gal/min.), resolve the insufficient fuel flow; refer to "15.12.6 Insufficient Fuel Flow Resolution" .

Section 15.12.6
Insufficient Fuel Flow Resolution

Perform the following steps to resolve the insufficient fuel flow:‪

1. Replace the fuel filter(s); refer to "2.14.1 Fuel Filter Housing Removal" .

   Note: Always fill the filter(s) with clean fuel oil before installing. Turn the filter(s) until they contact the gasket fully. Then turn them an additional two-thirds by hand.

2. Inspect the fuel lines for restrictions due to pinching, kinking, or other damage. If damage is found, repair as necessary; refer to OEM guidelines.
3. Inspect the fuel return check valve for restrictive movement.
4. Inspect the fuel pump drive assembly. If damage is found, repair as necessary; refer to "2.15 Fuel Pump" .
5. Verify repairs done to correct insufficient fuel flow; refer to "15.12.6.1 Test the Engine with Resolved Fuel Flow" .

Section 15.12.6.1
Test the Engine with Resolved Fuel Flow

Perform the following steps to determine if the fuel flow resolution resolved rough running or stalling:‪

PERSONAL INJURY ‪
To avoid injury before starting and running the engine, ensure the vehicle is parked on a level surface, parking brake is set, and the wheels are blocked. ‪

1. Start and run the engine.
2. Run the engine at idle with a no-load capacity for approximately five minutes, allowing the engine coolant to reach normal operating range, 88-96°C (190-205°F).
   1. If the engine is not running rough or stalling, no further troubleshooting is required. Shut down the engine.
   2. If the engine is running rough or stalling, shut down the engine. Contact Detroit Diesel Customer Support Center at 313-592-5800.