Detroit Diesel GHG14 Engine Idle Speed Balance Test

This illustration show you guide on how to perform idle speed balance test for Detroit Diesel GHG14 engine.

Incorporated into the MCM is the Idle Speed Balance (ISB) software which monitors the crankshaft speed variation per cylinder power stroke and compensates each fuel injector to allow for a smoother running engine at idle. The compensation values can be learned and stored in the EEPROM. ISB values are the percentage of adjustment that the MCM can make to a fuel injector to adjust for idle stability. It does not represent the total amount of available fuel per cylinder.

For diagnostic purposes, these values can be used to pinpoint a cylinder which is getting close to or at its maximum/minimum limit. The limit values are set to positive (+100) and negative (-100). A value above or below the acceptable limit indicates that the MCM software is compensating for a crankshaft speed variation. On a common rail system this can be caused by internal engine damage, fuel injector fueling issue or failure of a high pressure supply to a particular fuel injector.

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


For example, for a low injection rate (low fueling from fuel injector), the software will try to compensate for this fuel 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 fuel injector should only be replaced after a visual inspection of the fuel supply to the fuel injector is checked. If the value reaches (-100), this would indicate that the fuel injector is over-fueling to the point that the software cannot take out any more fuel.

Note : Mechanical failure can also cause a +100 or a -100 reading of ISB. Follow all of the troubleshooting procedures for the particular system to determine the root cause of the failure.


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Checking Idle Speed Balance

Check as follows:

Note : Fuel temp must be at least 10°C (50°F) and coolant temp must be at least 70°C (158°F).

1.Using DDDL 8.15, go to the “Service Routines” window and click on the “Idle Speed Balance” tab.

Detroit-Diesel-GHG14-Engine-Idle-Speed-Balance-Test-1 Detroit-Diesel-GHG14-Engine-Idle-Speed-Balance-Test-2


2.If there are any cylinders with a +100 or -100 Idle Speed Balance (ISB) value, run a compression test with DDDL 7.X.

2a If all cylinders pass the compression test, Go to step 3.

2b If any cylinder(s) fail, inspect for mechanical failure.

3.Run the engine at idle and monitor ISB parameters, making note of each cylinder that is showing a positive or negative 100% value.

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

4.Click on “RUN TEST” to reset the values for all cylinders to zero. If all cylinders have not updated within three minutes, run the engine to 1200 RPM for one minute and return to idle. This will cause the MCM software to relearn the ISB values.

Detroit-Diesel-GHG14-Engine-Idle-Speed-Balance-Test-3 Detroit-Diesel-GHG14-Engine-Idle-Speed-Balance-Test-4


Fill in the following chart with the ISB values. These can be used at a later date or may be required for another procedure.


5.Continue to monitor any cylinder(s) that have reached a positive or negative 100%. If the suspect cylinder is stuck at the limit of positive or negative 100%, check the following components:

Fuel line from fuel rail to fuel injector (kinked or plugged). Repair as necessary.Go to step 6.

Fuel line connection at fuel injector or fuel rail (leaking). Repair as necessary. Go to step 6.

Compression test; Repair as necessary. Go to step 6.

6.If a cylinder is constantly higher than +70% or lower than -70% and there are no other mechanical concerns with the engine, replace the fuel injector.

7.If Idle Speed Balance values (ISB) are out of range after performing repairs, contact Customer Support Center at 800-445-1980.


More repair case for Detroit,please refer to:Detroit Diesel Engine Repair.

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