Q: Load on truck's engine causes loud knocking noise

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When there is a load on my truck’s engine, there is a loud knocking noise. When I used a scanner, it registered a cylinder 5 misfire is detected. I have replaced the ignition coil, wires, and the plugs, but the problem still is existing. Can you tell me what is causing this knocking sound and give me advice on how to fix it?

Hello. It sounds like there may be a problem with the piston or the valves in cylinder 5. Loose rod bearings to the piston can cause a knocking noise and/or a misfire condition. A worn out piston can also cause these symptoms. It is possible for a misfire to be caused by burnt valves but this will usually cause a tapping noise in the engine.

Since you have already replaced the ignition coil, wires, and spark plugs it is likely that there is an internal engine problem. In this case it may be necessary to have the engine rebuilt or replaced with a new one.

I suggest having the car looked at by a certified technician who can diagnose the noise in your engine firsthand and suggest an accurate repair from there.

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