Cummins ISL-G Ignition System
The Cummins ISL-G ignition system is a capacitive discharge type. The ICM (Ignition Control Module) takes 12 volts and steps it up to 250-300 volts to the primary side of the coil. This high voltage uses less current and allows the coils to create less heat.
The ignition system is a coil-on-plug system that uses an ignition control module (ICM) to operate.
Spark timing is controlled by the engine control module (ECM). The ECM commands the ICM to energize the ignition coil for the present cylinder in the firing sequence over the ICM timing line in the engine harness. The coils are energized by the ICM through the charge voltage and primary return lines in the ignition harness.
The ECM requires an initial input from the Camshaft Speed Position Sensor for the engine to start. Once the ECM gets synchronization from this sensor and the Crankshaft Speed Position Sensor, the Crankshaft Speed Position sensor becomes the primary input for ignition timing. The ECM also uses input from the Intake Manifold Pressure Temperature Sensor to adjust how far to advance the timing of the spark.
The engine camshaft speed/position sensor provides engine speed and cylinder #1 compression stroke information to the ECM. This sensor generates a signal from the passing of seven cast protrusions located on the rear of the camshaft gear. An engine crankshaft position sensor mounted at the rear of the block is used to signal piston position during the stroke. Both of the ISL-G position sensors are hall-effect type and provide a DC high-low (5 to 0V) signal to the ECM. The engine crankshaft speed/position sensor is located on top of the flywheel housing. The information from this sensor is used by the ECM to determine crankshaft rotational speed and each cylinder’s piston position as it relates to degrees of crankshaft rotation.
The ISLG uses a coil-on-plug type of ignition coil. This coil mounts directly to the spark plug. The high voltage pulse from the secondary windings of the coil are delivered directly to the spark plug. Without traditional spark plug wires the system requires less maintenance and is more efficient.
Voltages are as follows:
⇒ Primary coil side (pins A & C): 250 – 300volts
⇒ Secondary coil side (kV spark voltage): Average is 15 – 20kV, up to 40kV.
Note: Spark kV will vary with:
⇒ engine condition
⇒ spark plug condition
⇒ engine load
⇒ fuel conditions
kV readings between all cylinders should be close in value. Any cylinder(s) that kV’s are not within the value of the rest, indicate a problem with that cylinder(s).
There are two methods of misfire detection used:
1. The first method uses the ICM to detect a misfiring cylinder over the secondary RETURN wire in the ignition harness. The ECM receives this information from the ICM over combustion detection (misfire) SIGNAL wire(s).
2. The second method uses crankshaft speed to detect a misfiring cylinder.
The ICM monitors individual spark plug voltage and misfires and reports it to the ECM as an input for diagnostic purposes only. Ignition timing and air/fuel mixture values are not affected by these signals.
The ICM provides kV and misfire detection as an input to the ECM for diagnostic fault code capability. This engine incorporates multiple spark discharge (MSD) technology that uses solid state devices to trigger the capacitor charge/discharge cycle very rapidly when the engine has low intake manifold pressure.
During this condition, there is a relatively small amount of air/fuel mixture in the cylinder, and the cylinder is relatively cool. It is possible for the flame created by the spark to extinguish, due to the low heat and sparse air/fuel mixture in the cylinder.
Possible causes for misfires:
⇒ Spark plugs past maintenance intervals
⇒ Damaged spark plugs or boots
⇒ Spark plugs not torqued properly
⇒ Malfunctioning coil
⇒ Shorted or open ignition harness
Misfires can send unburned fuel and oxygen to the catalytic converter, overheating it and damaging the substrate. Any misfires should be addressed to prevent progressive damage from occurring.
Knock detection is used for engine protection:
The knock sensor is an accelerometer which measures high frequency vibrations. The electronic control module (ECM) processes the voltage signals from the knock sensor to check for an elevated signal during the combustion cycle for each cylinder. They are two wire sensors.
The ISL-G has two knock sensors, each sensor monitors three cylinders. The location of the knock sensors is specific and the knock detection is calibrated for this position, therefore, knock sensors must not be repositioned from the original location. The knock sensors are located near the front and rear of the engine.
The sensors are piezoelectric type that produce a small AC current when the crystal inside vibrates with engine detonation. When detonation is sensed, the ECM retards engine timing until detonation is diminished. Over time, the ECM will attempt to restore normal timing if detonation diminishes. The ECM has three thresholds programmed into it for knock detection and prevention.
Light Knock: Lowest of the three thresholds, is designed to guard against damage from light to mild knock. The ECM will retard ignition timing and slightly de-rate the throttle. A yellow lamp will illuminate to warn the operator that light knock has been detected.
Heavy Knock: This warning will be activated if the light knock protection fails to eliminate the problem or a knock is detected that crosses the heavy knock threshold. The ECM will trigger a severe throttle de-rate and illuminate the red warning lamp.
Cold Knock Threshold: This provides severe protection while the engine is reaching a stable operating temperature. Time at this threshold is a function of coolant temperature at startup. The cold knock threshold is disabled when the engine temperature reaches 160°F (71°C).
Ignition system problems can be categorized into three areas:
1. No Starts – this is a engine crank no start condition. This is the easier ignition system condition to troubleshoot as the fault is active.
2. Misfires – Can be random and on one or multiple cylinders,
3. Knock Faults – These are harder to troubleshoot as conditions like overhead out of adjustment, air compressor timing, low cylinder compression, turbocharger, defective plugs and other ignition components may be the culprit.
NO START Troubleshooting:
The recommended practice to troubleshoot the system for a “NO START” conditions is to follow the OEM diagnostic procedures. In lieu of this; the steps below are steps that we have found to work during our troubleshooting of failed systems.
Step 1 – Determine if the coil is generating spark.
To determine if an ignition coil is operational and producing the high voltage required to create a spark at the plug, an ignition tester is recommended. this could be one of two:
⇒ A spark indicator – this tool gives you a good indication of the system working to produce voltage. Unfortunately, it is not a good indicator of the intensity of the spark.
⇒ A Cummins approved ignition spark tester, for the ISL-G engine, the COP must be kept nearly vertical during operation due to oil-filled cooling of the coil. The test kit adapter must be used to properly position the COP during spark testing on this engine. When using this tester, no attempt should be made to adjust the tester. The ignition coil tester is preset and is not adjustable. Attempts to adjust the tester will damage the tool.
Note: Follow Cummins recommended procedures on using the tool.
If a spark signal is being generated by the coils; the problem may be faulty spark plugs or internal engine damage. In very few cases the fault may be the ICM is incorrectly timing the firing sequence.
Step 2 – Determine if the coil is being charged by the ICM.
⇒ Check for charge voltage to be present at terminals A (charge voltage 250-300 volts) and C (secondary return) of the coil. This is the voltage supply from the ICM to charge the coil. If there is no voltage here; the ICM is not sending the signal to charge the coil, this may be due to missing timing signals, missing or inadequate power supply to ICM, or defective ICM.
Caution: Use caution when checking coil voltages, high voltage can cause a dangerous electrical shock.
⇒ Secondary resistance winding measurement for the COP resistance is taken between pin C of the 4-pin connector of coil and spark plug connector. The reading should be less than 20K ohms, if coil resistance is greater than 20K ohms, replace coil.
⇒ The end to end resistance of any of the wires in the ignition harness should be less than 10 ohms.
Note: Readings greater than 10 ohms, harness should be repaired or replaced.
The resistance of any wire to chassis ground should be 100K ohms or more, considered shorted to ground.
MISFIRE and KNOCK Troubleshooting:
Misfiring and Knock Fault conditions are harder to troubleshoot. Drive the vehicle in the conditions of normal operation: engine temperature, road condition, acceleration rates, passenger loads.
Knock Sensor – The sensor itself rarely fails, and typical failures may include:
⇒ Loose sensor connector
⇒ Corroded or damaged harness pins
⇒ Damaged wiring harness
⇒ Loose sensor mounting
⇒ Wrong location installation
Keep in mind that the knock sensors measure the high frequency vibration of the engine due to combustion knock. Knock may occur if the engine is supplied low quality fuel or if operated at excessive temperatures.
Other sources of high frequency vibration that may also cause knock faults include gear-driven components like air compressors or hydraulic pumps, driveline vibration, or a rough running engine due to low fuel pressure.
When the conditions exist, knock faults typically will occur when operated at full power, such as during wide open throttle acceleration.
Cummins prefers that you troubleshoot the knock sensors through INsite; very few details are given about the operation of the sensor.
The knock sensor is specifically designed for each particular engine and is not an interchangeable component.
The Cummins Knock sensors is biased at 2.5 volts, this means that the ECM provides a voltage on the signal line.
This is done to avoid noise and interference associated with all ground circuits. The sensor itself divides the bias voltage in half because of its internal resistance. The knock circuit due to its higher voltage level (bias voltage) will not pick up any ground noise interference.
The bias voltage also lets the ECM know when the knock sensor circuit has either open or short circuited.
When the sensor detects engine knock, it drops the voltage down to a lower level; the ECM sees this as noise and de-rates accordingly.
Knock Sensor Resistance
Cummins does not provide a resistance value for the sensor. But when measured the sensor reads 4.880M ohms.
Note: High engine harness resistance will also influence sensor reading, and may cause a fake knock code reading or false codes. Harness resistance must be less than 10 ohms for each individual circuit.
Component Connector Views and Pin-Outs