6.7L Ford Powerstroke Diesel

Injector Return Line Plug

(Replaces CH-50377 / CH50377-A)

An Essential Tool for diagnosing low rail pressure

In the event of a rail pressure control issue (typically low rail pressure) on a 6.7L Powerstroke the injector return line plug can be a valuable part of the diagnostic process. One possible cause of low rail pressure is an injector that is returning too much fuel back to the return rail and fuel tank.

In the event of a no-start scenario with low rail pressure, we recommend following the GM procedure of electrically unplugging each injector one at a time, removing the return line from the injector, plugging the open point on the return line with a return line plug, and then cranking the engine for 15 seconds.  If any fuel is observed to flow from the injector return port, the injector is suspect and may need to be replaced.

In the event that the engine runs but actual rail pressure is less than desired, it is recommended to test for excessive injector return flow with the engine idling. In order to do this, it is absolutely necessary to use an fuel line block-off plug to seal any open connections on the return rail. Piezo injectors require back pressure on the return side in order to function. If insufficient back pressure is present, the injector will not fire and the engine will not run.  The test is performed by using a graduate to measure the return flow from each injector while idling the engine for one minute. Any injector that exceeds the specified return flow volume or is substantially higher than the others should be replaced.

As an alternative to using an injection line block-off cap, the return line cap eliminates the need to remove the one-time-use high pressure injection line.