The wife is pulling into the local McD's in her 2000 5.4 Expy (130,000 miles) and as she is slowing down 25-30mph she hears what sounds like a rock hitting the bottom of the vehicle. Then all of the sudden the engine starts to run very rough and is knocking very loud thru the throttle body.

Knowing that these engines are notorious for launching spark plugs I pulled all of the plugs last night. The #2 & #3 cylinders (Middle two on drivers side) were wet and covered with oil/gas. Checked all COP's and all appeared to test fine. Replaced all plugs and fired it back up, still running rough and still a loud knock coming from the throttle body area? Any ideas, I can record the sound if that helps anybody?

Thanks Guys!

 

Pull the valve/rocker cover and check the rocker arms on that side.

 

Thanks, I actually took compression tests on #2 & #3 cylinders and they were both 150-175psi. I just wanted to rule out major engine problems before I start searching for a replacement motor. Surely somebody else has experienced the same issue, even if it is a bad motor I'm sure this isn't the first one. Thanks for the help!

 

That's not good - nope! haven't heard of this problem . The only thing that resembles that is when #4 is missing , you'll get a loud knock on acceleration.

A valve ? You check all cylinders for compresion?

Is your knock sensor plugged in? The pcm can't adjust timing without that sensor plugged in . Maybe it's that sensor that's bad ..?

Idunno , Good Luck .

Let us know when you figure this one out ..

 

Well I pulled the Valve Cover off of the drivers side on Friday. Found a broken valve spring on #4 and the rocker arm was just laying between the head and valve cover, is this a common failure? When it happened my wife was maybe going 20mph and under little to no load? Hopefully it didn't damage anything else.

 

might have damaged a piston when it came apartt

 

Installed a new Valve Spring and Re-Installed the Rocker arm, fired it up and no Knock and it ran like normal Doesn't appear to have caused any other damage, amazing!

Good thing I didn't take it to Ford they would have wanted to install a new motor.