Hi. I own an '83 Firebird with the 305.
There is an intermittent noise that two mechanic friends have finally caught and identified as an exhaust leak. I cannot find it, and it is understandably driving me crazy. In an attempt to locate it, I have replaced the spark plugs; removed the air-injection pipes at the engine (it still injects air into the cat for the sake of N.Y. smog tests), replaced the cat (had it welded), tightened the torque-converter-to-flywheel bolts;, tightened the front pulley bolts, checked the snugness of the E.G.R. valve (cleaned it too);, ETC, ETC, ETC. I cannot visually locate any smears of soot, anywhere.
Remember that this problem comes and goes. I have been assured that is an exhaust leak, so I should not be concerned about a bearing or transmission or equally expensive problem.. Any ideas????????????
THANK YOU

 

Do you have headers? If yes check your header bolts or replace the gaskets. If no headers, still check the manifold bolts, but if they have never been touched, that probably isn't the problem. What about the O2 sensor? BTW how did your mechanic friends deduce that its an exhaust leak? Could they find it?

 

Car is stock. Has 90,000 miles. Iron exhaust manifolds. The 1st owner had never touched the exhaust securing nuts.
I had thought that the noise was....Well I had no idea. This is why I was (am) so concerned. [It is NOT a hard metallic noise]. Whether a bearing, a waterpump bearing, fuel pump, ring, piston-pin, head gasket, or a tranny/ torque converter issue, the noise should logically be there all the time. Remember that this is my logic, and not necessarily correct. I had even considered the intake-air heater stove door.
Neither friend had been able to find the source of the noise. It seems to disappear whenever we begin to look for it. It appears, usually after a little bit of warm-up. Continues for a bit. And more often than not, eventually goes back into hiding. Needs at least 1500 r.p.m. to become apparent. Occurs in gear or neutral.
Both friends said "Exhaust noise" without any hesitation.
I had thought that the mystery was solved when I discovered that the accelerator cable was rattling against the hollow plastic cover over the intermittent wiper mechanism. The noise seems louder with the windows up, so I figured that we might be looking for a resonance.
My ears indicate that the noise comes through the center of the floor hump, where the two cables go through grommets in the floor.
This has nothing to do with the issue, (does it?), but my intake manifold gasket is peeing onto the floor, and if it is sunny on Saturday, I will replace it. Have a good evening.
Seth

 

Check your manifold bolts. My car has 68k miles on it, and when I installed headers, 3 of my exhaust manifold bolts unscrewed with my finger.

 

Perhaps its a loose rocker arm or two. They tend to loosen after a while and sound similar to a minor exhaust leak but usually are inaudible from the car unless they are out quite a bit. Its easy to check though. Using a large screwdriver have one of your friends rev the car to the RPM where you hear the noise and place the screwdier on the valve cover and your ear on the handle end and it will amplify the sound so you can find or eliminate this as one possible cause. Easy fix too if this is the prob do a search here and you will find all you need to adjust the rockers.

 

Twenty-one year old exhaust fasteners. That shall be a trip.
I will do the smart thing first. RUST PENETRANT.
Will also examine the O2 sensor, but the sensor is a long-shot.
While working on the intake gaskets, I will also do the valve-cover gaskets (from the factory, we have rubber caulking, not real gaskets). This will give me future access to the rockers.
I really appreciate the input from you guys. Thanks.