So I just put a set of refurbished injectors on my truck 01 3500. Two cups came out and I put news rings and reinstalled them. (Was not aware of need for to thread lock.) Pressure in coolant.... So I tare it back apart to seal the cups. The two injectors that came out with the cups had major carbon build up. Out of curiosity I pulled the next one in line and it has a lot of carbon build up on it too. What can cause such dramatic build up in so short a time?