The process of testing a HEUI injector is referred to as a "flush and flow". This involves installing the injector in our test stand, flushing out all contaminants, and checking the flow against the various voltage parameters. Scan tool "buzz tests" and "cylinder contribution tests" alone are not accurate indicators of an injector's integrity. The "flush and flow" test is the only way to determine the precise measurement of fuel output based on the exact microvoltage outputs of the vehicle ECU. If you question an injectors performance, or if you are pulling injectors for some other reason and want them tested, arrange to have them sent to our facility for a "flush and flow". Refer to the "External Oring Kit" for your cost for new external seals. Testing charges are waved for each faulty injector replaced. Feel free to call our parts department at 800-891-8038 with any questions.