[TNT89Bronco]

I am trying to nail down a sound that seems to be coming from the passenger side, right by the front tire. Quite frankly, it sounds like there is a lawnmower running under the hood. I have noticed it ever since I got it about four months ago. You can't hear it outside, when it is just sitting still and the engine is running. Nor can you hear it, with the window down and your are driving. It can really only be heard with the window up.

I did notice, that today when we were heading to the mountains, and I had the cruise control set on 65 (2,800 rpm), I could hear it when we were heading up an incline or any type of grade heading up. However, when we were heading either flat or downhill, the noise went away. Couldn't hear a thing. The RPM didn't really drop .much, maybe 200 RPM at the most. But it does seem to be heard when it is under "load".

Like I said, sitting still, I can't hear it, even if I rev the engine. The pitch doesn't seem to get higher, when the RPM or speed increases. Just gets a little louder, when I am moving down the street or highway.

I suspect that it is an exhaust link, but where would it be leaking from that would make that type of noise? Like I said...sitting still...nothing. And at freeway speeds, now LOUD, but just a muffled lawnmower muffler.

It does not sound metallic in nature or like a grinding noise...but seriously, a lawnmower doing 65!!!

 

[Glayd]

Heya TNT,
did you check the serpentine belt? I had a noise I couldnt find for the longest time similar to yours and it turned out that I had gotten antifreeze on the belt by mistake. Finally took the belt off and cleaned it with detergent soap (purple power or something like that) and the noise went away. It had actually gotten so irritating that I thought it was the AC compressor and I was ready to replace the compressor. Glad it was just the belt.

Good Luck

 

[Bronco_Loco]

Sounds like you may have a cracked exhaust manifold. Probably caused by bad motor mounts allowing the engine to twist from the torque when under load, and opening up the crack making it louder. When the load is reduced or at idle, the exhaust may settle back into place, reducing the noise.

Had this problem on my '87, but left it unattended since it's an off-road only rig. The manifold eventually broke completely in two between the 3rd & fourth cylinder on the passenger side.

 

[TNT89Bronco]

I will check the belt, but the exhaust manifold sounds like a possibility, based on what I think that would sound like. I will have to figure out a way to check. Do you think the crack would be visible or so small that you couldn't see it?

 

[Gacknar]

Cracked pass side Exhaust manifold, typical.
Replace them both with a set of shortie headers.

 

[MustangSally232]

Definitely sounds like an exhaust leak. I had the same issue about a month after installing my headers, a few of the bolts on the passenger side loosened up and it was leaking between the head and header, luckily it did not damage the gasket and I was able to just re-tighten everything. I'd say check all the exhaust hardware and look for any cracks, and headers would definitely be a nice upgrade.

 

[FirstPriority]

exhaust leak:rockon

 

[tonyroc14]

TNT do you also get a slight vibration? This is what mine sounds like. You're driving and your engine sounds nice, and then all of a sudden there is a buffeting type sound, such as a lawn mower. I get this same noise, but I also get a vibration. It's not a violent or rough vibration but its there. Also, my motor mounts are fawked. So this could possibly be my problem. I can't afford new headers tho

 

[inteva6184]

Sounds like a broken egr tube.

 

[Bronco_Loco]

I will check the belt, but the exhaust manifold sounds like a possibility, based on what I think that would sound like. I will have to figure out a way to check. Do you think the crack would be visible or so small that you couldn't see it?

If it's opening up enough to hear it inside, chances are you can probably see the crack...if you can't see it from the top, look for puffs of exhaust smoke coming out around the manifold, egr, etc. Maybe even have someone hold the brake while it's in gear and give it some gas to torque the engine a bit. If the engine moves more than a fraction of an inch, you'll want to replace the motor mounts too.

 

[TNT89Bronco]

Ok..today I went out and checked under the hood and looked for any type of crack in both the EGR tube and the passenger side exhaust manifold. I checked as best as I could, but couldn't find or feel any type of crack. However, I was checking the driver's side exhaust manifold, and I see what I suspect is a twisted off bolt where the exhaust manifold attaches to the exhaust. I didn't do a lot of other checking, but took this picture to see if it is what I think it is. If so, I suspect that this might be the sound that I am hearing? Thoughts?

 

[thin blue line]

exhaust leaks are a pain to find on manifolds. or even at the y pipe.

 

[cajunrebel]

That is not a twisted off bolt. It actually installs through the bottom. Your seeing the back side of the bolt. That manifold actually looks pretty good.

 

[TNT89Bronco]

Thanks! The search for the noise goes on!

 

[inteva6184]

Just so you know the egr youre going to have a very hard time locating. The part that cracks is deep under the upper intake and is covered by heat wrap. I only found mine because I was doing intake gaskets I couldnt locate where my "lawnmower" type sound was coming from either. One way to tell would be to have someone stand on the brakes and load up the engine until the noise begins. Then listen for it mine sounded like it was a knock coming from the head.

 

[miesk5]

yo,
Use a short section of garden hose to help track it down; once you think you found it, place a lonf scredwriver or any long enug metal rod against the suspect area or component(s)..

Chk the secondary air check valves (btwn eng & firewall); tube to cat converter too
mu ck valve rusted and sounded just like a bad muffler