97 Mustang GT to 2011 Crown Vic Swap 95k Miles (Knock at idle)


New Member
Jan 27, 2020
Hello! I recently did a swap on my 97 mustang GT to a 2011 crown vic police engine.

It had 95k miles, came straight out of a rear end wrecked police vehicle.

Ive been driving it for about 1000 miles and it started with a light knocking sound at idle then got slightly worse.

It goes away at about 1500 rpm and sometimes it'll go away completely at idle and won't even hear it until i start driving and stop again.

Very strange knock, sounds like its coming from the middle front or middle passenger side.

Barely hear it when just starting car, if i rev and let it idle at startup itll start the knock.

Someone told me it could be a rocker arm??

Any help is appreciated!
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SN Certified Technician
Aug 14, 2009
Houston Texas
It had 95k miles, came straight out of a rear end wrecked police vehicle.
Cars in police service spend soooooooooooo much of there life idling running the AC and keeping the radio on. This means that mileage is a poor indicator of wear. In fact many Police fleet cars will have an external Hobbs hour meter to keep track of running time. It's for this reason I generally recommend avoiding salvage motors in police service.

Let me ask, when the motor was first started how did it run?

Did the police motor have an external oil cooler?

Recommend getting yourself a mechanics stethoscope and see if you can better isolate where the noise is coming from. Try probing all around valve cover, intake manifold, exhaust manifold.

It might also be worth your while to pull the valve covers and perform a visual inspection. Note, pay attention to the long valve cover bolts on the outside edge. I made the mistake of backing them out not paying attention. The bolts pressed against the shock towers and it messed up the threads. It would have been smarter to have cut off the wiring harness stand offs that are not used on the Mustang.