2008 F250 5.4L Knock
 

Hi,

I was towing a bobcat today( not normal for me ) and my truck has developed a significant knock. I have owned the vehicle for about 10k miles/year and generally only tow about 3k lbs, this load was more like 8k. Before this trip the engine made no noises out of the ordinary.

The noise is loudest at idle and become inaudible at about 2200 rpm. The sound can be heard in the cab. It is loudest behind the wheels. Almost sounds like it is from the bottom end or possibly transmission.

It is a hard knock and is loudest when initial started for about 10 seconds and quietens down slightly... it is not always there but mostly. Almost sounds like a bad input shaft bearing but I don't think so.

Fluids look good oil is 5w20 motorcraft




Thanks for any input regarding how to diagnose this.

The key to diagnosing any noise is to locate it you can do it yourself. A mechanics stethoscope is cheap and one of the best tools for locating a noise there is.

First remove the serpentine belt and start the vehicle, if there is no noise, then suspect one of the front end accessory drive components like the belt tensioner, one of the front cover pulleys, A/C, P/S ALT, water pump..... work from a process of area elimination.

If the noise is present with belt removed take the stethoscope and place it at the front cover just below the cam covers.... Then at the very front of the cam covers, next move down the top of the cam covers to the back.

If it sounds like its under the truck crawl under and place the scope against the oil pan then the underside of the block below the exhaust manifolds.

This way you should be able to hear where is the noise the loudest. Hopefully that will narrow down the area where it makes the most noise.... Give that a try

I will listen to it today with a stethoscope as suggested. However I don't think this will provide absolute diagnosis. I unplugged the VCT solenoids to no affect. I am considering an oil pressure gauge.
The engine runs smooth and performs good.

Any other suggestions on steps to take? Or should I just take it to the dealership?

You can always check the oil pressure, but I would think if you didnt have any oil pressure you'd be hearing the lifters chattering away. It didnt sound like a piston slap to me, but the video sound can only tell me so much .

It didnt sound like cam phaser noise, because usually when the truck starts you dont hear it, but one the engine starts to get warmer and warmer the cam phaser noise becomes pretty noticeable.

Some of the others here may chime in with some possibilities of what it could be, which may help in finding other items for you to look at and check as well.

I put a stethoscope on it to try to isolate where the sound is coming from.

The sound is loudest coming from the passenger side catalytic converter. I could hear the noise softly if I had the scope on the manifold and also very slightly if it was on the valve cover. No noise if it was on the block.

Any thoughts regarding the source?

Hmmm. I wonder if your honeycomb in your cat came lose and is making the knock, I have heard of it happening. Is that the original catalytic converter?

It could be or possibly some noise in the engine resonating in the cat? Apparently there was a TSB regarding earlier F-150 5.4 around 2000 and the solution was to wrap the cat in sound deadening... Not certain my next steps i might still take it into ford but would like further diagnosis if possible.

Cracked flex plate perhaps, did you put the scope on the bell housing towards the trans?

I did and no noise from the trany. I also inspected the flex plate as best I could by removing the inspection cover, and everything looked good.

I'm experiencing the exact same noise in my 2011 E250 5.4L, right to a T. Runs perfectly well, just makes an awful rattling noise just like that. One told me it could be main bearing gone, another also said a cracked flywheel.

It would be REALLY great if someone had the same issue and knew what it was!!