Mysttoo Common Rail Fuel Injector Block-Off Caps 5-piece M12–M20, Carbon-Steel, Corrosion-Resistant

When you need to diagnose leaking injectors, intermittent combustion noises, or verify fuel pressure on modern diesel engines, having the right block-off caps makes the job faster and cleaner. This Mysttoo kit includes five thread sizes (M12, M14, M16, M18, M20) to fit injector lines used across many Cummins, Duramax, and Ford Powerstroke engines from the early 2000s through 2022. Each cap is machined from carbon steel and finished to resist corrosion and thread damage during repeated service use.

Which engines and model years will this cap set work with?

This set is engineered to cover the most common injector thread sizes found in late-model diesel trucks. It fits 2003–2022 Cummins, 2001–2022 Duramax, and 2008–2022 Ford Powerstroke applications where common-rail injector block-off caps are required for diagnostic procedures. Compatibility depends on factory injector line thread standards, so verify thread pitch before use.

• Includes M12x1.5, M14x1.5, M16x1.5, M18x1.5, M20x1.5 sizes
• Covers many Cummins, Duramax, and Powerstroke engines across 2001–2022 ranges
• Check vehicle service manual or existing injector line threads for confirmation

How do these caps help during fuel rail diagnostics?

Block-off caps let you isolate cylinders by stopping fuel supply to a specific injector, which helps identify leaking injectors or abnormal combustion. They also facilitate fuel pressure tests and controlled shutoffs without damaging injector threads or common-rail fittings. Use them during pressure checks, knock source isolation, or when performing injector replacement prep.

• Seal injector ports to isolate cylinders during testing
• Enable accurate fuel pressure readings by preventing leaks
• Reduce mess and contamination when removing injector lines

What is the build quality and durability of these block-off caps?

Mysttoo manufactures these caps from carbon steel, chosen for strength and resistance to thread stripping under torque. The surfaces are treated to lower the risk of rust and to extend service life even in harsh workshop environments. Each cap is precision-threaded to form a reliable seal while remaining reusable for multiple diagnostic cycles.

• Carbon-steel construction for high tensile strength
• Anti-rust finish to withstand garage conditions
• Precision threads reduce risk of galling and ensure a tight seal

What comes in the package and what warranty is offered?

The pack contains five injector caps in the five most-used metric thread sizes for diesel common rails. Mysttoo backs the set with a 24-month quality guarantee to protect against manufacturing defects, and their support team is available for fitment or troubleshooting questions. Keep receipts and record fitment details for warranty claims.

• Five caps: M12x1.5, M14x1.5, M16x1.5, M18x1.5, M20x1.5
• 24-month quality guarantee from Mysttoo
• Customer support available for fitment questions

Who is this for: This Mysttoo 5PCS block-off cap set is aimed at professional diesel technicians, independent mechanics, and experienced DIY truck owners who perform injector diagnostics or maintenance on Cummins, Duramax, and Ford Powerstroke engines. If you frequently test fuel pressure, isolate injector faults, or service common-rail systems, this durable, multi-size kit simplifies the process and protects injector threads during work.