AccurateDiesel Duramax LB7 LLY Diesel Injector Block-Off Tool Cap

When a Duramax common rail engine will not start, one of the very first things to check is fuel rail pressure. If the pressure is less than 2,500 PSI (LB), one of the most likely causes is a defective injector that is returning excess fuel back to the tank. A return flow volume test will verify if excessive return flow is the problem. This cap is then used to identify the individual cylinder that is at fault. The injection line is removed for one cylinder at a time and the cap installed on the fuel rail in place of the injection line. When the cylinder with the offending injector is capped, the rail pressure will rise and the truck will start. In some cases it can be highly advantageous to have multiple caps, because several injectors that return slightly too much fuel can have the same effect as a single injector with extremely excessive return flow. To purchase a complete set of block off tools, please see our other Amazon listings. The injector block off tool can also be useful for diagnosing engine knocking sounds that may be attributable to an injector or a single cylinder problem particularly on engines where this capability is not available through the scan tool, or a bi-directional scan tool is not available. At least one of these would also be a great addition to the glovebox kit of every Duramax owner. When an injector malfunctions on a common rail engine damage to a piston or cylinder can occur very rapidly. When a common rail engine begins to misfire and blow excessive white smoke, the owner is highly advised to turn the engine off and call a tow truck to prevent major engine damage from occurring. An alternative would be to temporarily cap the injector for that cylinder for a short period. When working on high pressure fuel systems, always educate yourself first by reading appropriate factory service information, use common sense, and, above all, WEAR SAFETY GOGGLES!