DD15 Troubleshooting – Section 16.12 Isc Values

Section 16.12
Isc Values

Incorporated into the MCM is the ISC software which monitors the crank wheel speed variation per segment and compensates each injector to allow a smoother running engine. When the engine is at or around idle speed, the compensation values can be learned and stored in the EEPROM. ‪

For diagnostic purposes these values can be used to pinpoint a cylinder which is getting close or at its maximum/minimum limit. The limit valves are set to positive (+100) and negative (-100). At the positive value, the MCM software is compensating for an injection rate that is low‪

On a common rail system this can be caused by an injector fueling issue (such as problems with actuators, lack of amplification or plugged nozzle) or failure of a high pressure supply to a particular injector (such as plugging of inlet particle filter of injector).‪

On a unit pump system this can be caused by the unit pump, high pressure line, transfer tube, or injector (nozzle). At the negative value, the MCM software is compensating for an injection rate that is high. On a common rail system this can be caused by an injector fueling issue. On a unit pump system this can be caused by the unit pump or injector (nozzle).‪

If the ISC values are 0, this indicates no compensation is needed. Values of +40 and -40 are not uncommon for a new fuel system. If values reach +70 to +80 and -70 to -80, injection quantities are reaching their limits and should be noted. If values are at +100 and -100, the respective cylinders should be checked.‪

For diagnostics more emphasis needs to be placed on a cylinder in the positive range due to this 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.‪

Section 16.12.1
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.