8d • General discussion
4D56 Engine knock
🚨 Real Diagnosis Case Study – Mitsubishi 4D56 Engine Knock
Customer complaint: Engine knock at idle that almost disappeared when the revs were brought up.
At first inspection, we suspected possible lower-end engine damage.
To confirm, we cut open the oil filter and found metallic contamination throughout the filter media — a strong sign of internal engine failure.
After clear communication with the customer and discussing the likely repair costs and next steps, approval was given to remove the engine for further inspection.
Once the sump was removed, the fault was confirmed: the crankshaft had completely cracked behind cylinder 1.
At idle, the broken crank was allowing movement and creating the knock.
As revs increased, the two sections would momentarily lock together, reducing the noise and allowing all cylinders to operate more smoothly.
💡 This is why correct diagnosis matters. Guesswork can cost thousands. Proper testing, customer care, and communication are just as important as turning spanners.
Have you ever heard an engine knock that disappeared with revs?
#Mitsubishi #4D56 #EngineFailure #MechanicLife #Diagnostics #DieselEngine #WorkshopRealities
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4D56 Engine knock
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