DD15 Faulty Fuel Injector Troubleshooting

For diagnostics more emphasis needs to be placed on a cylinder in the positive or negative range when checking the ISC value. The positive range implies that more fueling is needed to maintain a smooth running engine. The corresponding high positive value would only be compensating for the low performing cylinder.‪

Example : For a low injection rate (low fueling from injector), the software will try to compensate for this injector by increasing its pulse width to smooth out the engine. The value will go positive until the engine is performing properly. If the value reaches (+100), no more compensation can occur. The injector should be replaced only after a visual inspection of the fuel supply to the injector is checked.‪

The negative range (-100) can be a sign of an injector not sealing internally.‪

Checking ISC Values

Check as follows:‪

  1. Using DDDL 7.0, go to the “Instrumentation” window and click on the “All Instruments” tab
  2. Scroll down to the “MCM” section and locate the parameters “Idle Speed Balance Values: Cylinder #1” thru cylinder 6.
  3. Start and bring engine up to operating temperature (over 140°F/60°C).
  4. Ensure engine is at idle.
  5. Monitor ISC parameters making note of each cylinder that is showing a positive 100% value.

    Note: During the learning process some cylinders may reach the positive 100% limit, but will only stay there for a short period of time. Looking at the parameters using the chart function can help determine an injector that is stuck at the 100% limit compared to an injector that reached the limit for a short time. See the next two illustrations.

    Note: If all cylinders have not updated within 3 minutes, run the engine to 1200 RPM for 1 minute and return to idle. This will cause the MCM software to relearn the ISC values.

  6. Continue to monitor cylinder(s) that reached a positive 100%. If the suspect cylinder is stuck at the limit for longer than 3 minutes, check the following components:
    • Fuel line from rail to injector (kinked or plugged)
    • Fuel line connection at injector or rail (leaking)
  7. If fuel line and connections are OK, replace injector.

Test the Engine with Repaired Fuel Injector

Perform the following to determine if the fuel injector repair resolved excessive white smoke:‪

  1. Start and run the engine.
  2. Run the engine at idle with a no-load for approximately five minutes, allowing the engine coolant to reach normal operating range.
  3. Visually inspect exhaust for excessive white smoke.
    1. If the engine exhaust emission appears normal, no further troubleshooting is required. Shut down the engine.
    2. If the engine exhaust emission is excessively white, shut down the engine. Call the Detroit Diesel Customer Support Center (313–592–5800).

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