63679 Mercruiser BUMPER, BELL HOUSING

Table 1
Dual Clean Emission Module Aftertreatment System
Aftertreatment DEF Pump DEF Injectors DEF Pressure Line Color
1 1 2, 3 Blue
1 2 1, 4 Green
2 1 2, 3 Yellow
2 2 1, 4 Red
Illustration 1 g06539999
The 994K aftertreatment contains two CEM packages built into one package. This represents one circuit for the aftertreatment system and there are three other circuits that have the same parts and function.
(1) Exhaust inlet
(2) Inlet Nitrogen Oxide (NOx) sensor
(3) Diesel Exhaust Fluid (DEF) injector
(4) Outlet NOx sensor
(5) Exhaust out
(6) Catalyst brick
(7) DEF supply line
(8) Coolant return to engine line
(9) DEF pump
(10) Coolant supply from engine line
(11) Coolant diverter valve
(12) DEF backflow valve
(13) DEF tank
(14) Coolant supply connector
(15) Suction connector
(16) Backflow connector
(17) Coolant return connector
(18) DEF suction line
(19) DEF backflow line
(20) Dosing Control Unit (DCU)
(21) Aftertreatment Electronic Control Module (ECM)The purpose of Diesel Exhaust Fluid (DEF) is to create a Selective Catalytic Reduction (SCR) process to take place in the exhaust system to reduce Nitrogen Oxides (NOx).When the engine is keyed on but not running, DEF is not being injected into the system. When the engine is running, the DEF may be too cold or frozen to be injected. When the ambient or tank temperatures are cold enough, the DEF control unit (DCU) opens the coolant diverter valve to allow engine coolant to flow through the DEF tank to warm the system. The DCU also activates the heater circuits in the lines and pump to prevent DEF from freezing in the lines and pump. The time it takes to thaw the system depends on the tank temperature. Since the system always starts with empty lines, the pump activates to fill the lines with fluid before DEF injection begins.Once the system is thawed and primed, the DEF will be injected into the exhaust system when the DEF tank and SCR temperatures are warm enough. If the system does not heat up after duration of time, a diagnostic code will become active.Note: Typical usage for DEF is 1-3% of diesel fluid. The DEF tank should be refilled at the same time as the fuel tank.The DEF system has three operation modes:1. DEF Priming ModeSince the system always starts with empty lines, the pump activates to fill the lines with fluid before DEF injection begins. Priming will start when engine speed is greater than 450 rpm, DEF tank temp is greater than −6° C (21.2° F), and SCR inlet temperature is greater