Spent 8 hours chasing a phantom knock on a 6.7 Powerstroke

Customer complaint was a loud knock at idle. Checked the usual stuff first, injectors, lifters, even pulled the oil pan. Nothing. Finally found it was a broken motor mount bracket letting the engine rock just enough to tap the firewall. Took me all day to figure that out. Anyone run into something like this before?

3 comments

3 Comments

sarahpark14d ago

Remember that time on a 5.9 Cummins where the knock was just the fan shroud cracked and vibrating. Spent half a day on valve train noise before I saw it wobble at the right RPM. Those phantom sounds are the worst.

felixm2914d ago

Man, that "phantom knock" thing hits home. When you finally found it was the motor mount bracket, did the knock change at all when you put it in gear or gave it a little throttle? Or was it just a steady tap no matter what?

pat_murray5314d ago

Ugh, phantom knocks are the worst! @sarahpark is right, it's always something stupid like a shroud or a bracket. Feels like a victory when you find it, but also like you wasted a whole day.