Hidden Exhaust Leak?
Freshman User
Joined: Sep 2001
Posts: 39
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Hidden Exhaust Leak?
I have an exhaust leak that I cannot find. Even a muffler shop can't find where it is coming from. I could barely hear ir when I first got truck with 56K. Since then I have added Bassani equal length shorty headers, off-road Y-pipe and Gibson cat-back system. Exhaust leak noise has gotten louder and now I have 88K on truck. Sounds like it is coming from back of engine. Not like one cylinder popping from the headers. More like a leaking muffler but behind engine. I removed the crossover on back of heads believing it had a hole, but it did not. It had no carbon evidence of a leak. There are 2 valve looking things at back of engine. Do these leak exhaust? Has anyone else had a mystery exhaust noise? I even removed the egr tube from intake to egr and inspected it for holes and nothing. When I remove the EGR tube from the valve and start the engine it makes a noise similar to what I can hear under a load, but much louder of course, as the mystery leak. Any thoughts. I changed the complete exhaust system and the noise has not changed. It has just gotten worse as the miles rack up.
Posting Guru
Joined: Apr 2002
Posts: 1,471
Likes: 3
From: Greenwood In. USA
Hidden Exhaust Leak?
I assume this is a V8. It should be on pasenger side either directly connected to the air pump or in same general area. Follow the lines from the pump to the engine the "dump" valve will be between the pump and the engine. It dumps the output of the pump when you decellerate preventing a backfire in the exhaust. It is controlled usally by manifold vacumn.
Gasman
Gasman
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Joined: Jan 2001
Posts: 1,124
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From: Rural Florida Panhandle
Hidden Exhaust Leak?
You have two check valves in the exhaust system. One of them is hose connected to the pipe at the back of the heads. The other is along the passenger side or maybe to the rear. The first one dumps fresh air into the exhaust at the heads, controlled by the computer and vacuum. The other dumps fresh air into the converter via the little pipe going to it.
Either of these check valves can fail, allowing an exhaust leak. There are two failure modes; burn/rust out and sticking in the open position. I have had both. They only cost $12 -$15 at Autozone, but are a little chore to replace.
In this system, there are vacuum-operated valves which control the air from the smog pump, and there are electrical solenoids which control the vacuum signal to them. I have had all the above to fail, though not on the same vehicle.
Winford
Either of these check valves can fail, allowing an exhaust leak. There are two failure modes; burn/rust out and sticking in the open position. I have had both. They only cost $12 -$15 at Autozone, but are a little chore to replace.
In this system, there are vacuum-operated valves which control the air from the smog pump, and there are electrical solenoids which control the vacuum signal to them. I have had all the above to fail, though not on the same vehicle.
Winford
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Senior User
Joined: Jul 2002
Posts: 219
Likes: 0
From: SW Michigan
Hidden Exhaust Leak?
I have a 92xlt w/Lightning motor. I've been looking for a exhaust leak on the back of the motor for over a year. You say there are two valves? I think I have to pull the manifold to get my hands behind the motor. Are the valves available from underneath?It sounds like a weekend job. Tanks Sav
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Lead Driver
Joined: Sep 2002
Posts: 9,540
Likes: 2,031
From: North Texas
Hidden Exhaust Leak?
That is where mine leaks from too. It is some stupid check valve that is a PITA to replace. It is a one way valve but, I plugged mine with JB Weld to fool the inspectors! Hahahaha 
I will replace it once it cools off down here in Texas
I will replace it once it cools off down here in Texas
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