Tech Features

This section contains bulletins and pertinent information for installers or repair facilities. Many of the bulletins in this section deal with very common installation or unit problems. Always check for pertinent bulletins before beginning any installation or if a problem occurs with a unit. Check back often. We add bulletins as information becomes available. If you have any questions please call the warranty department at 800-841-6060 or email us at
Exhaust Backpressure Testing
Excessive Backpressure

Diagnosing excessive backpressure, the result of a restricted exhaust system, is easily performed with common hand tools and a fuel pump pressure gauge. A restricted exhaust system may cause performance problems or even serious engine damage.

Depending on the engine application there are two convenient places to tap into the exhaust system. If the engine is equipped with a thermactor pump that introduces fresh air into the exhaust manifold through multiple pipes, connect the fuel pump pressure gauge to the point where these pipes join (Figure 1). Be sure to remove any check valve that may be present. Alternately, remove the oxygen sensor and using the proper fitting connect the pressure gauge (Figure 2).

Some AERA members have found that a small hole drilled into the header pipe can also be used for testing. Later the hole can be plugged with a rivet.

Start the engine and permit it to reach normal operating temperature if possible. At idle there should be no more than 1.25 psi of exhaust backpressure. Accelerate the engine to 2,000 rpm and observe the pressure gauge. The reading should not exceed 3 psi.

A restricted exhaust system is present if the readings exceed the recommended values at either speed. Inspect the entire exhaust system for a collapsed pipe, internal muffler failure or heat distress. If no obvious reason for the excessive backpressure can be found, it is most likely created by a restricted catalytic converter. Replace the converter.

                                                                                                                                                                                                        —– The AERA Technical Committee