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Robert R
Robert R, ASE Certified Technician
Category: Jeep
Satisfied Customers: 4455
Experience:  ASE Master Certified, Jeep Certified
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Loud knocking/tapping that does not go away. Frequency

Customer Question

Loud knocking/tapping that does not go away. Frequency increases with rise in rpms
JA: Where exactly do you think the noise is coming from? And how long has this been going on?
Customer: I think it is coming from the mid to lower portion on the cylinders , above the oil pan
JA: What is the model/year of your Jeep?
Customer: 2002 Jeep Grand Cherokee
JA: Are you fixing your Grand Cherokee yourself? What have you tried so far?
Customer: I am trying to fix it. I tried putting a couple tablespoons of oil in each spark plug hole and then starting it to see if the sound would temporarily disapper. (Saw this on a YouTube video to diagnose piston slap)
JA: Anything else you want the mechanic to know before I connect you?
Customer: When it started, I was towing a boat. Later that day the front differential broke
Submitted: 9 months ago.
Category: Jeep
Expert:  Robert R replied 9 months ago.

Hello, welcome and thanks for asking your question. My name is*****'m a Certified Auto Technician with 29+ years experience. I will do my best to assist you. please keep in mind that I may need to ask questions of you before I can answer. When you reply please feel free to add as much detailed information as possible pertaining to your concern.

What engine is in your Grand Cherokee?

Can you post the last 8 digits of the VIN and the miles on the odometer so that I can do some research on this concern for you?

Thank you,


Customer: replied 9 months ago.
4.0 6 cylinder . 191*** miles
Expert:  Robert R replied 9 months ago.

4.0l engines are known for knocking sounds due to piston slap or loose wrist pins.

How is your oil pressure? Does it have a gauge?

Customer: replied 9 months ago.
Oil pressure is fine. Can I fix this at home?
Expert:  Robert R replied 9 months ago.

With good oil pressure, the rod, main and cam bearings should be ok. With good oil pressure another possibility is a stretched timing chain although a chain noise normally reduces in intensity as engine rpm goes up.

Depending on your knowledge and tools available, this can be done on your driveway. Cylinder head and oil pan would need to be removed in order to remove the pistons. It would be best to diagnose the noise so that you can narrow it down to a particular cylinder, this way, you can go straight for that single cylinder and replace only one piston if you want to do this as cheaply as possible, otherwise it may be a good idea to replace all pistons, all piston rings, rod bearings and have the cylinder head valve job performed...

Keep me posted and let me know if you have any additional questions...

Thank you,