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Q: Constant knocking sound from engine

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My car makes a constant knocking/pinging sound which increases when the transmission is engaged, it consumes lot of fuel. It used up the engine oil just three weeks after servicing.

My car has 80000 miles.
My car has an automatic transmission.

A: Hello and thank you for contacting YourMech...

Hello and thank you for contacting YourMechanic. The knocking sound is coming from the flex plate in the back of the engine. The flex plate is what drives the torque converter to the transmission. The flex plate is probably cracked or broken. This will make a constant knocking or pinging sound and gets louder when the transmission is engaged.

Your fuel consumption could be caused by the engine having to work harder to make up the power loss between the engine and transmission. I recommend having the flex plate replaced along with the torque converter.

Plus, you will want to check the front seal and the seals on the input shaft to the transmission for any damage. Usually soon after repairing a broken flex plate, the transmission front seal tends to leak. I recommend replacing the front seal when the transmission is out.

Before you replace any parts, I recommend seeking out a professional, preferably a YourMechanic professional to assist you with a thorough diagnosis of the noise coming from your engine.

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