I know you found the leak but another option I like is get a piece of tube long enough and put on end to your ear and run the other end along where the leak could be coming from. Very simple and effective.
As for the gasket use muffler joint compound, goes on wet, dries hard and makes a good seal...or just weld that s***
Found it! Over the Easter weekend I had my brother plug the tailpipe with a blanket while I crawled around under the exhaust. With the exhaust plugged the leak was really simple to locate: the joint between the first and second cat. I replaced these last summer, but it appears that the gasket is not thick enough to bridge the gap. My plan is to try using two gaskets. Yay or nay?
I'm following up on all this over a year later. I replaced the gasket between cats 1 and 2 (I used 2 gaskets) last year, with no change in the sound. At that point I gave up and figured I'd eventually just replace the whole exhaust when it finally bit the dust.
Fast forward to last Friday. I was under the truck greasing the driveshafts when I noticed that I was missing a significant chunk of the rear O2 sensor gasket. I picked up the gasket and two nuts today and climbed under the rig tonight when I got home. To my surprise, there was nothing left of the original nuts except some rust the the stud threads. I removed the heat shield, O2 sensor and the remnants of the old gasket. After cleaning the mating surface of the exhaust bung and chasing the stud threads with a die (M8x1.25) I installed the new gasket, the O2 sensor and the heat shield. I installed the new nuts with a little dab of antiseize and snugged them down. Voila, no more buzz!
I have a similar leak on my 97 original cats, right between the two. take a look or listen to the cat shields as you tap on them all around, the buzzing you mentioned could quite possibly be one of them. I had a similar buzzing under load that was quickly remedied with a little mechanic's twine wrapped around tourniquet style.
Bumping this up....
I have a new to me 1997 series 80. I'm pretty certain I have an exhaust leak, but it's not like any other exhaust leak I've ever dealt with. Normally I can hear it and/or smell it and then when on the freeway it's not a problem as any fumes aren't going to linger at those speeds.
With my 80, I can tell it's def running a little rich. Initially upon getting it I was throwing a code for the EGR and figured it was bad but ended up finding two disconnected vacuum lines running to it. I reset the codes and it's not coming back so far. The truck still seems to be running rich and I can detect the fumes near the back of the truck. It's missing the converters so that could be part of it.
The biggest problem I'm having and why I'm posting is that when driving I'm getting pounding headache everytime I drive it. It almost seems to be worse on the freeway which boggles my mind. Like I said any exhaust leak I've ever dealt with usually isn't a problem when the car is moving unless it's really large. The truck runs nice and quiet but then again I haven't really poked around underneath with it running. Normally you can hear a good sized exhaust leak without too much trouble. At first I was trying to convince myself each time that there was some othe problem like being tired or not enough coffee. At this point I'm convinced driving this thing is giving me a pounding headache each time. It usually happens within 10 minutes even with the windows up. The only thing that can really be causing this is exhaust getting into the cabin somehow, even though I never smell anything.
80's are somewhat new to me and the exhaust routing going inside and outside the frame is new and odd to me. I'm going to try and digging into this over the weekend, but I'm certainly open to suggestions. Is there any malfunction or broken part that might allow the HAVC to pull air in from under the hood? Any other common things that go wrong that's specific to the 80's that I might not be aware of?
This is a dangerous situation, you don't want to pass out at the wheel so work hard to figure out where the leak is. When I am looking for an exhaust leak I use a 4'+ fuel line or some kind of fairly heat resistant tubing, then crawl around stick one end in your ear and then move the other end around to different connections on the system with the engine on.. You will know when you find the leak.. My guess is that is is from the cats forward, could even be the EGR system.
Sounds like your allergic to something the seller left in the rig. Sit in it for 20+ minutes with the engine NOT running to test the theory. No headache = exhaust problem .
All good stuff guys. I thought about the possibility of being allergic to stuff but at 41 years old I'm pretty much allergic to nothing and have been in so many cars over the years I can't imagine it would be that suddenly.
I did put the code reader on again and I have the EGR code again. I think it was p0401 or something like that. It appears someone previously has disconnected the check engine light, so I can't rely on waiting for that to come on.
Anyway I'm fully aware of how dangerous this is. My wife and I took it tonight for dinner as I kind of wanted to see if she noticed it or got a head ache. She said she eventually kind of did. I'm pretty sure extra rich exhaust is getting in somehow. The faulty EGR will make it run rich won't it? Not that I'm trying to kill my wife or anything but I wanted to rule out some kind of allergen.
In regards to testing it I was likely going to use the soapy water method and then pressurize the exhaust with either the shop vac or using my compressor somehow with the regulator turned way down.
Either way it's all weird as an exhaust leak big enough to give you a headache that quickly is usually easy to hear or smell.
Check the rear quarter panels for holes, my 95 had them (part of the reason the back got cut off) but it was rotted just behind the rear wheel, letting fumes into the cabin by the rear sub...
I've always just started it (when cold) and held my hand over the exhaust to find leaks...but I like the shop vac idea that someone above posted...
Didn't read all posts but old timer tought me:
Engine running, use compressed air over whole exhaust , when air noise changes in pitch you found the leak. Who really wants to breath in sea foam while finding a leak.....
Looks like it might be directly below the rear heater. Maybe you have a hole around the pipes where they go into the truck?
Also in that area, only higher up, would be the gas tank cover plate. Did someone service the tank and not seal it up well?
I put some JB weld on it for now and will let it cure. I did notice that the rear heater pipes were in that area. If I get energetic Ill see about the fuel pump access. That's just removal of the rear seat and pull up some carpet right?
