Mercury Mariner Outboard 225 3 Litre Service Manual 1994, Page 117Get this manual
Enrichment System The Electronic Control Unit (ECU) electrically controls the enrichment valve to provide rich fuel charge for starting cold engineThe ECU monitors engine coolant temperature (thru the
Fuel Enrichment operates as function of time and block temperature aWhen block is cold and keyswitch is turned to "ON" position (engine not running), enrichment valve will provide fuel forsecondsEnrichment valve will continue to provide fuel while engine is cranking until block temperature reaches approximately 122 (50 C)at which point it will no longer provide fuelWhen block is hot (normal operating temperature140 10 155 F) enrichment valve will provide fuel for approximately 12 second when key is turned positionThe valve will not provide fuel to during cranking at temperatures above 122 F
temperature sensor) and ignition timing (thru the crank position sensor)The ECU electronically opens the enrichment valve for varying lengths of limethe colder the engine, the longer the valve remains openThe ECU also advances ignition timingthe colder the engine, the more the ignition timing is advanced to improve cold starting characteristicsFuel is gravity fed to the enrichment valve from the top car-