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Michael, Ford Senior Master Tech
Category: Mercury
Satisfied Customers: 670
Experience:  Ford Senior Master Tech with 22 yrs experience with Ford, Lincoln, and Mercury
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Mercury Grand Marquis Triton 4.6 litre has knocking noise in

Customer Question

Mercury Grand Marquis Triton 4.6 litre has knocking noise in the motor. Only has 88,000 actual miles
JA: Where exactly do you think the noise is coming from? And how long has this been going on?
Customer: pulled valve cover and everything looked good. going to short each spark plug to try to identify which cylinder could be a problem.
JA: What year is your Grand Marquis?
Customer: 1999, also disconnected serpentine belt to be sure no accessories were making the noise. when using a stethocope each head and the intake manifold all give this same knock.
JA: Are you fixing your Grand Marquis yourself? What have you tried so far?
Customer: Yes, I have years of mechanical experience. I removed valve cover and checked overhead cam
JA: Anything else you want the mechanic to know before I connect you?
Customer: Used stethoscope to try to pinpoint knock. the knock is the same on both heads. Tomorrow going to short out each spark plug to try to see if the noise changes. Car has 88,000 actual miles.
Submitted: 8 months ago.
Category: Mercury
Expert:  Michael replied 8 months ago.

Hello, my name is***** will be assisting you today. Give me a moment ot review your information and get right with you.

When do you hear the noise the most.

Hot or Cold?

Idle or under load?

If you are in neutral and rev the engine do you hear the noise more?

Customer: replied 8 months ago.
Knock is present all the time.
Expert:  Michael replied 8 months ago.

A knock that is always present and isn't affected by load or temperature is typically a valve train noise, which you've inspected for, or a broken piston/skirt. Rarely a carbon ridge the top of the cylinder can make a noise. I recommend continuing with your current diagnostic path and cancelling cylinders by unplugging injectors one by one while it's running. If the noise goes away it's probably a piston or wrist pin problem.

If not and the noise is coming from the timing chain area pull the timing cover and inspect the timing chain guides. They are plastic and can wear causing chain slack and noise. This is typically a loud tap from the front of the engine.

Expert:  Michael replied 8 months ago.

If I can be of any further assistance do not hesitate to ask. If not, please rate my service. If for any reason you feel you cannot rate my service five stars please let me know.