1999 "EE" 90, 115 FFI, 150, 175 V4, V6 FFI Outboards Service Manual, P/N 787024, Page 54Get this manual
The Power Distribution Panel supplies the 12 and 26 volts necessary to operate the ECUIt also contains number of relays and fuses to protect or control these circuitsThe ECU controls ignition coil primary circuit operation, and contains the circuits necessary to supply voltage and trigger firingSignals from the crank position sensor allow the ECU to determine proper cylinder firing sequenceInternal circuits also allow the ECU to detect open loads in the coil primary circuits, and set and store corresponding service codes FFI Combustion Process
The FFI combustion process functions in two modes; stratified and homogeneousThe engine is started in homogeneous, idles and trolls in stratified, then smoothly transitions again to homogeneous as the engine moves to higher RPM During startup, fuel is injected with the piston low in the cylinderAirfuel is mixed by turbulence, and multiple plug firings occur to ensure quick starting and complete combustionDuring idle and trolling, multiple plug firings continue for each cylinder combustion eventSpark is timed to occur as fuel reaches the spark plug tip, then is programmed to continue in multi-strike modeDue to fuel air density at low RPM, and fuel actually spraying on the plug tip, repeated plug firing ensures complete combustionAt higher RPM, the fuel injectors supply fuel earlier in the firing sequencePistons are farther down the cylinder, and airfuel is mixed by turbulenceIn this mode the mixture is more combustible, so fewer firings per combustion event will occurVery low amperage is required to sustain either stratified or homogeneous operation