GM-51614 allows the DPF injector to be tested outside of the exhaust system. Once the DPF injector is removed from the exhaust, it is reattached to the fuel line upside down, and the block-off plate of GM-51614 is installed on the exhaust manifold to prevent exhaust leaks. The test fixture block is installed on the injector bracket to retain the injector, and a hose is installed over the injector nozzle to direct the fuel released into one of the test tubes from the GM-45873 fuel return volume test kit. The engine is then started, and the injector is triggered for a specific amount of time. The fuel injected during this time is measured to determine if the injector is operating properly.