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Cranking Amps (Diesel Engine) Waveform Notes
The purpose of this particular waveform is two fold:-
- To measure the amperage required to crank the engine
- To evaluate the relative compressions
The amperage required to crank the engine will largely depend on many factors, these include the capacity of the engine, the number of cylinders, the viscosity of the oil, the condition of the starter motor, the condition of the starters wiring circuit and the compressions in the cylinders.
The current for a typical 4 cylinder diesel engine is in the region of 200 to 300 amps. The compressions can be compared against each other by monitoring the current required to push each cylinder up on its compression stroke. The better the compression the higher the current demand and vice versa. It is therefore important that the current draw on each cylinder is equal.
This test is only a comparison against each cylinder and is not a substitute for a physical compression test with a suitable gauge. Due to inaccessibility on a diesel engine, this test can be extremely useful when diagnosing problems on the compression/ignition diesel engine.
NOTE: when conducting compression tests on a diesel engine ensure that the appropriate gauge is used (diesels have much higher compression than petrol engines). Also make certain that the fuel supply to the injectors is stopped by electrically isolating the fuel cut-off solenoid.
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