The Wideband O2 air/fuel ratio UEGO gauge is a must if you want to maximize your engine's power and safety. When tuning an engine, accurate air/fuel ratio data is critical because running with too rich of an AFR can cause a loss of power, and running a lean AFR can result in serious engine damage. AEM's digital Wideband AFR UEGO gauge can quickly alert you to even a .1 change in air/fuel ratio and provide enough time to shut down an engine before damage occurs.