Bdelaney820

I have a 2006 5.4 3V with 76k miles. The truck has developed what sounds like a lower end knock only upon cold start after sitting all night. The knock is only audible at idle also (6-700 rpm). The knock is present until the engine is warm. Only once the truck is fully warmed up to operating temp the knock disappears, and the engine is quiet and functions perfect. I live in PA, and started noticing the "knock" when the weather started getting cold around October. I am running 5w-30 full synthetic motor oil with motorcraft oil filter. The sound is hard to pinpoint exactly where it is coming from. It seemed to be coming from the catalytic converters, and they were replaced. The knock is still present. Does anyone have any experience with this, or can point me in the right direction?

BadFish523

I know you said it sounds like its coming from the cats but have you checked the manifold for a crack? A cracked manifold will sometimes stop making the tick (not really a knock) after it warms up due to the manifold expanding and sealing the crack.

Bdelaney820

The passenger side manifold/gasket/studs were just replaced about 4000 miles ago so id have to suspect that not the issue...

BadFish523

Ok, could be chain rattle from broken chain guides? Get a video or 2 and upload to youtube then post a link here. Video is very helpful for noises.

Bdelaney820

I can post a few videos. I dont believe it to be timing chain either as you cant hear the "knock" at all from the front where the chain is. You can really hear it underneath the truck though. It almost sounds as if it is coming from somewhere between engine/transmission....

Dirttracker18

OEM Ford manifold and high quality gaskets?

My first pasenger manifold was an aftermarket part and it lasted about a year before it warped and started making noise. The replacement, under warranty, lasted 3 months. After that I acquired a good used Ford manifold and put in Felpro gaskets. No issues since.

Just food for thought. However if you went through this before you likely know the difference in sound between a leaky manifold and a knock.

Bdelaney820

Brand new Ford manifold/gasket/studs/nuts were put on. I just posted a video to YouTube. It is dark but my phone is under the driver side. The knock actually doesn't start until about 10 seconds after truck is started. Video here:
https://youtu.be/bTYq8tKppb8

BadFish523

Doesn't sound like a manifold to me.

Bdelaney820

Yeah I'm fairly certain it's not a manifold as well