My son just bought this car and its been running fine. Now there is a knock and I'm stumped on what's causing this.
Symptoms:
When the engine warms up, there is a light thumping sound coming from the # 8 piston/head area. It's intermittent while at an idle.
The thumping is intermittent when running up the RPM's. But the thumping does get a little louder.
The # 8 cylinder has a lower compression than the rest.
When we unplug the fuel injector the thumping in steady.

We've changed the plugs...

2000 Mustang Knocking from cylinder/Head