4.6 loud shreiking noise?

[CallMeSyd]

2004 4.6L Explorer NBX. When I start the engine it makes a loud sound like blowing high pressure air through a loosely kinked garden hose, but the sound goes away completely when it settles into idle. Also does it when revving or accelerating, always, but then back at idle again, it's gone. The sound does not change after vehicle warms up. When it first started, it sounded more like a deep metal on metal squealing sound almost like a pulley bearing going or internal shaft bearing and was very loud and higher pitched, but not as high pitched as a squealing belt. The sound changed after I ran it a few times to now sounding as I originally described (the air through a hose thing). It has stopped changing and now sounds the same day after day. Best I can describe it is sounding like a bobcat or mountain lion growl/scream. It seems to be coming from the drivers side front of the engine. I have removed the serpentine belt entirely to rule out anything like a pulley, pump, compressor, alternator... so it's not any of that. Oil pressure is perfect, temps perfect, runs and drives perfect, no leaks. Because I have driven it and the sound is constant (every time it starts up or under acceleration), never changes, and it's still running and driving just fine, I feel I can rule out anything internal or any bearings or anything that could wear and/or get worse. I originally worried that it was a cam, but the sound seems to come from below the head. Also, again, if it was a cam, the noise would change or be gone by now, if the cam didn't seize up, but none of that. It is too loud to be any type of vacuum or intake leak. The ONLY thing I can think of is that it is some kind of exhaust leak at the manifold. It has done this ever since I bought it, and after realizing that it isn't anything catastrophic and it's still running and driving, I just haven't had time to look farther into it. However, I'm tired of it sounding like a big angry wild cat every time I take off from a stop. It appears that someone drilled and scrambled out the catalytic converter, so I can only assume that there isn't some type of blockage in the exhaust. I stuck a screwdriver in through the cat where they drilled it and confirmed that it's empty inside. Before I go through the nightmare of trying to remove the exhaust manifold, is there something I've missed? I have never heard an exhaust leak sound like this. Could it be the exhaust blowing across the gasket making this horrible noise? Maybe my studs broke? Could this have been caused by the apparent clogged catalytic converter causing so much back pressure that it broke the studs or blew the gasket out? Is it possible that there's another cause for back pressure that is causing this? I'd just really like some feedback. And if I solve this, maybe someone with this nightmare will find our solution in the future.

 

[LMHmedchem]

If there is a leak in your exhaust at the manifold that is causing a loud noise, I would think that there would be a jet of very hot exhaust at the leak. The exhaust would have to be very accelerated to cause a loud sound so I think that you would be able to detect it. If you had a smoke machine or something that would create a visible (non-flammable) vapor you could shoot in a puff of smoke and find the jet that way. You may also be able to feel it with your hand but I would be very careful and only try that when you have just started up and the exhaust is not up to full temperature. An inferred thermometer could also work, as could any thermal scan device that can give you a picture in infrared.

I suppose you could also try to seal around the manifold with a bead of high temp RTV or something like that. If it eliminates or reduces the sound even for a short time then you know where your problem is.

Can you see if any of the studs are missing?

LMHmedchem

 

[CallMeSyd]

I will try and look later to see if there are broken studs. It's such a tight fit in there. I guess I'll go ahead and plan for the vehicle to be out of service for a while so I can go ahead and work on figuring this out.

 

[LMHmedchem]

Hopefully someone here has had the same issue and will at least be able to post what the problem is.

You mentioned checking the belt system. Did you make very sure that the bearings in all 3 of your idler pulleys are good? Do they spin freely? I would expect that you would be able to tell that the sound is coming from the belt area if they had gone bad but those bearings do tend to go after nearly 20 years. I guess you don't have to deal with road salt like we do around here.

I generally seem to be able to find quite a number of things that need repair and most of them don't fix my problem, which is really quite a bore.

LMHmedchem

 

[CallMeSyd]

Hopefully someone here has had the same issue and will at least be able to post what the problem is.

You mentioned checking the belt system. Did you make very sure that the bearings in all 3 of your idler pulleys are good? Do they spin freely? I would expect that you would be able to tell that the sound is coming from the belt area if they had gone bad but those bearings do tend to go after nearly 20 years. I guess you don't have to deal with road salt like we do around here.

I generally seem to be able to find quite a number of things that need repair and most of them don't fix my problem, which is really quite a bore.

LMHmedchem

Thanks so much for your reply. I pulled the belt off completely so that nothing was spinning and the sound was still there. I've worked on trucks and cars for years and I've never seen or heard anything like this. I haven't had time to check the exhaust but hopefully I can get to it today. There's really nothing else I can think of. If it's not the exhaust then it's gotta be something internal. I wouldn't think so because it hasn't changed at all... usually if it's anything like that it will get worse or fail over time but that hasn't been the case. I'm honestly stumped. Is there a way to post a video clip on here?

 

[Turdle]

Timing chains contacting internal surfaces of timing cover? Look for thread titled " timing chain ooops" , posted by jah81592 in the street trucks sub forum. I bumped said thread to new posts, you might find it there

 

[CallMeSyd]

Timing chains contacting internal surfaces of timing cover? Look for thread titled " timing chain ooops" , posted by jah81592 in the street trucks sub forum. I bumped said thread to new posts, you might find it there

Thanks. I checked out the thread but that sounds nothing like what's going on with mine. The way they described it is just not the same. If i suspected timing chain at all i would have already opened it up first thing. I was supposed to look at it today... again... but I had to deal with something else and wasn't able. I am going to record a video of it for you guys when I'm able. Next few days are already planned out by my wife, but I'll get to it asap.

 

[CallMeSyd]

Few pics. About to record noise on video.

 

[CallMeSyd]

Alright here are the videos of the noise. Again, i have verified that it is not belt or pulley related. Only does it when starting cold. Then stops at warm idle. Then it does it every time you hit the throttle.

 

[Turdle]

Sorry but it sounds like a chain

 

[CallMeSyd]

Alright. So, I finally got some time to take a look at the exhaust. Turns out, there's a compound issue at play. I had checked quickly underneath once at the exhaust and noticed that the cats had been scrambled out. I could see that it had been done on both sides, and I guess I had assumed that they had fixed whatever flow issue they had. However, I guess that was a mistake and you should never assume anything. They scrambled the front 2 cats, but not the rear, and of course, the rear one is clogged. I disconnected the exhaust between the cats and muffler and confirmed there is flow, but nothing near what it should be. And of course, there is an exhaust leak on the drivers side. Seems to just be the flange coming from the manifold to the y pipe, so far as I can tell. I'm assuming the back pressure from the clogged exhaust is all blowing out causing that horrible noise. So, my plan is to cut out the final cat and replace it with a bypass pipe. Then, I can seal the exhaust leak at the flange and retest, hoping the noise will be gone, please God.

 

[CallMeSyd]

Problem solved. Cut out the last cat and welded up a bypass pipe. Purrs like a kitten and man does the exhaust ever sound good with no cats. Still minor exhaust leak to fix, but it's 100 percent better and doesn't make that horrible noise anymore.