Diagnosing Exhaust Leaks Upstream of 02 Sensor

Question

I have a 96 Chevy G10 van with a 5.0. For a while I have suspected the vehicle may have had an exhaust leak. However, I also suspected the leak may have been around the manifold, and unfortunately, I am not really sure how to find a leak at that particular location (no lift for one thing). Eventually one shop reported a small leak on the right exhaust flange, but could not repair it. While, I was quite happy because this seemed to be a reasonable solution to some long running driveablity problems, both the shop that I had hoped would repair it and another were unable to find the leak.

As such, I have a few questions relating to leaks around the manifold of an engine.

First, could a leak in that location cause the following issues: ragged idle, loud engine noise (particularly during acceleration when cold), strong exhaust odor outside the vehicle, vibrations or shakiness felt in steering wheel at higher speeds, and sluggish acceleration.

Second, how do the symptoms of a leak upstream the O2 sensor differ from those downstream it (if at all)?

Finally, how can the average individual go about finding such a leak given that accessibility to the pipes is not ideal?

Thanks.

Answer 1

An exhaust leak can cause your O2 sensor to read incorrectly. Many of these symptoms could be related if the O2 is reading different than the actual reading and adjusting the A/F mixture. Shakiness on the highway is not related. That is likely tire balance, pitman arm, idler arm, tie rods, or ball joints.

Upstream O2 is used to determine the A/F ratio of the mixture burned in the engine. Downstream O2 is used to verify the cat is burning off hydrocarbons. A leak before the first O2 sensor can cause it to read incorrectly and and incorrectly adjust the A/F mixture. Between the first and second sensor, it may throw a CEL. After the second sensor, it will just be louder, with no affects on the engine / tuning. Any leak may allow exhaust gases into the cabin.

I use a stethoscope to find exhaust leaks. Go over the pipe and joint, listen for air movement and exhaust noises. It will get much louder when you are near the leak and you may feel the exhaust pushing out of the leak. Look for black marks where the exhaust was exiting. Use a small mirror to look all around the gasket areas.

Another thought... If you've ever used sea foam or power foam, it causes a lot of smoke from your exhaust. You may be able to use this and see if smoke comes out form the manifold area.

Edit: My stethoscope is ear protection, a hole drilled in one side with a vacuum line inserted. At the end of the vacuum line is a piece of metal brake line with a 45* bend. This allows my to point the tip into tight spots exactly where I want it. When I put it on, I put the bit of vacuum line in/against my ear. Using hearing protection helps filter out the other noises of the engine running.