Package Includes:
12mm Fuel Rail Cap: M12 x 1.5, 12mm internal thread nuts.
14mm Fuel Rail Cap: M14 x 1.5, 14mm internal thread nuts.
16mm Fuel Rail Cap: M16 x 1.5, 16mm internal thread nuts.
18mm Fuel Rail Cap: M18 x 1.5, 18mm internal thread nuts.
20mm Fuel Rail Cap: M20 x 1.5, 20mm internal thread nuts.

Fitment:
M12 (12mm) Fuel Rail Cap:
Fits for Ford 6.4L 2008-2010.

M14 (14mm) Fuel Rail Cap:
Fits for Ford 6.7L 2011-2022
Fits for Cummins 5.9L 2003-2009
Fits for Duramax 6.6L 2001-2005
Fits for Duramax 6.6L 2017-2022

M16 (16mm) Fuel Rail Cap:
Fits for Cummins 6.7L 2019-2022.

M18 (18mm) Fuel Rail Cap:
Fits for Duramax 6.6L 2011-2016

M20 (20mm) Fuel Rail Cap:
Fits for Cummins 6.7L 2007-2018
Fits for Duramax 6.6L 2006-2010.

Function:
Just install the fuel rail block-off caps on the fuel rail. If the fuel pressure increases, it means that there is a problem with the injector.

These fuel rail block off caps are used to block the fuel supply to cylinders or seal the common rail line. This helps to find problems with the engine, for example by checking for faulty diesel injectors or finding the cause of engine knock sounds by checking each cylinder on its own.

Multiple block-off tools can be useful, as multiple injectors returning small amounts of fuel may mimic symptoms of a single injector with excessive fuel return.