yo JESS,
WELCOME!
This is by Walker;
TESTING FOR AN EXHAUST SYSTEM RESTRICTION
These tests are used to determine if blockages exist in the exhaust system, creating excessive backpressure. The following test can help determine the location of an exhaust restriction.
ENGINE VACUUM TEST
The intent of the vacuum test is to determine if there is a blockage or restriction in the entire exhaust system. It may or may not indicate converter problems. This test can be performed using any suitable engine vacuum source. After the vacuum gauge is connected to a vacuum source, readings are noted at idle and then again at 2,500 RPMs. As engine speeds vary, readings should initially drop slightly, then rise to within 2 to 3 inches of the vacuum level established at idle. A large drop of 8-10 inches of vacuum typically indicates an exhaust restriction. Erratic swings of the vacuum readings may indicate periodic blockages caused by loose components temporarily blocking the exhaust system. Remember that vacuum levels are also affected by factors other than exhaust system restriction, including valve and ignition timing.
BACKPRESSURE TESTING
If a vehicle fails the engine backpressure vacuum test, you can pinpoint the component in the exhaust system causing the concern by measuring backpressure at different points in the exhaust system. These measurements can typically be made through the O2 sensor ports. Start by inspecting the system for crushed, bent, or otherwise restricted exhaust pipes. Replace or repair as required. If the system passes the visual inspection, remove the most rearward O2 sensor. This sensor is typically located directly after the converter. The use of heat or penetrating oil and a back and forth motion may help if the sensor threads are rusty. Most O2 sensors use an 18mm-threaded port, so one adapter fits many applications. Install adapter in the O2 port and tighten to manufacturer specifications. Then connect the gauge hose to the adapter. Begin by reading, and taking note of, pressure at idle and at 2500RPM. On most vehicles, at idle back pressure should not be higher than 1 psi. At 2500 RPMs the reading should not be higher than 3 psi. If the readings are high at this point, the blockage probably exists downstream of the test point, which typically means it is in the muffler or resonator. If the back pressure is okay at this location, move to the O2 sensor just ahead of the converter and retest. If the back pressure is high at this point, the converter is causing the issue. If the O2 sensor ahead of the converter tests okay, then the restriction is most likely in the y-pipe assembly, or there could be an internal restriction in the air gap pipe located between the exhaust manifold and the converter.
http://www.walkerexhaust.com/support/inspections
>-
