After converting your CP4 to a CP3, the stainless steel 9th injector return plug with o-ring is used to block the non-utilized fuel return loop. The CP4 utilizes the additional return plumbing where the CP3 does not. By not closing off/sealing this return port, you place the engine at risk for hard starting, fuel leaks or sub-par performance.

Made from stainless steel and comes with the 0-ring.