4.6 engine knock
 

2003 f150 4.6l 2v @70,000 miles on it

Hello, I recently developed a loud engine knock while driving down the highway, I drove it home and it didn’t seem to get worse but the sound seems to get faster with the rpm of the motor.

I got a #4 misfire code so I checked plug and the plug was bad , still in the threads but stuck, I managed to unscrew the plug and put a new plug in, sort of using the new plug as a tap, now it threads in fine and comes out fine but the knock is still there.

The truck also idles strange , revs then slows then revs then slows.

i tried a stethoscope and all I hear is the knocking everywhere I put it with a little bit different pitch

Also I noticed when I start the motor it doesn’t make the noise until the truck fires up

It sounds like you have an exhaust leak.

Check your exhaust manifold.

Check ALL the plugs. One or more may be loose. They need to be torqued to 28 ft/lb.

Thanks for the replies, tomorrow I will Check all plugs, I guess I figured the one with the miss was the only one but i should have checked them all.

as for the exhaust leak, I probably do, I know I have a leaky egr tube but the sound is very distinct and vibration on the coil pack, even the plug I just fixed. I should have recorded it before the plug fix and after.

And the way it happened driving with a misfire and instant rattling, slight power loss but still moving


I’ll go at it tomorrow, thanks for the help

If you feel vibration on the coil pack, the spark plug is loose! Keep driving it like that, the plug will eject, taking the threads with it. Sounds to me like you should change ALL the plugs, use Motorcraft plugs, and look down the plug holes, clean carbon off the seats. Torque to 28 ft/lb.

Just to clarify I’m not driving it, it’s been parked since this happened and I’ve been forced to drive old reliable my 1996 Corolla with 272k on it.

just got done checking all plugs and all but one we’re fine, none were stuck or loose the only one that was questionable had some debris on the end , not sure if it was picked up on the way out or not but replaced it anyway.

and the noise is still there but it seems to run better.

i guess next would be to remove the serpentine belt and see if it’s an accessory?

thanks again

Ok so ran it without the belt for a few seconds just long enough to tell the noise is not an accessory.

then changed oil to use motorcraft filter instead of stp and now engine cranks but doesn’t start

with accesive cranking there there definitely is no knock while cranking.

i guess I’m leaning to exhaust leak but the sound sounds like a hammer hitting metal, but now I have to figure out why it isn’t starting

I suggest taking it to a professional at this point.

Check for fuel, check for spark. Try starting it with your foot part way down on the gas pedal.

I would get a pro to listen to the knock. You may have a bearing going out. If you can post a video of the knock we may be able to help.

Got it started
I’m trying to upload a video

Well my dad is a frame tech and an old push rod v8 guy so I’m trying to get him over to listen.
i couldn’t figure out how to get the video up

Upload it to You Tube and post a link.

Here is link to video