8.1 Horizon information

Diebroke1

New Member
Sep 25, 2017
11
Chesapeake Bay, Land of Pleasent Living
Boat Info
1998 37' Sundancer. Original RayMarine electronics. Ipad with Garmin, Navionics apps.
Engines
Horizon [2] 380hp--V drives
I have a '98 37DA with 8.1 Horizon engines. port engine runes fine, reaches max rpm. Starboard engine idles surge, sometimes stalls, cruises ok. but can't reach max rpm. after investigating plugs, wires and distributor, fuel pump etc. have come to the conclusion its a sensor. It's a FI engine so I know they have sensors to control the air/fuel. Thinking it has a MAS sensor behind the spark arrestor, I was surprised to discover it has none[???]. Where should I look and what am I looking for?
 
Fault code? If you hook the ECM to a code reader/laptop you may get your answer.
 
Without oxygen sensors, the ecm relies on pre-mapped fuel curves. These can be based on either intake airflow measured from a mass airflow sensor, or engine load information from a MAP sensor.

If there isn't a mass airflow sensor, then the ecm uses the engine rpm and MAP (manifold absolute pressure) sensor data to adjust injector pulse width.

3,000 rpm in neutral is very different from 3,000 rpm in gear, and requires much less fuel flow to hit 3,000 rpm in neutral. The engine will have a high manifold vacuum reading while revving in neutral, and the MAP sensor provides the data to help the ecm "see" this condition.

Sorry for the long winded version.......heres the short version......swap the MAP sensor from one motor to the other.
 
^^^^Wouldn't failure of that sensor just put the engine in GUARDIAN mode and trigger an alarm?
 
^^^^Wouldn't failure of that sensor just put the engine in GUARDIAN mode and trigger an alarm?

Not necessarily - if the sensor has failed in such a fashion that it still sends data to the ECU, but the data is rubbish, the ECU will still act on that data. Only when a sensor fails in a fashion that it sends no data, or data "out of range" will the ECU "know" there is a fault.


Also, you need to have a decent understanding of how the system works to understand what faults a fault code represents.... For instance, on an engine with no oxygen sensors, if the mas/map sensor sends erroneous data to the ECU resulting in a lean condition, the ECU may register a knock sensor fault.
 
Without oxygen sensors, the ecm relies on pre-mapped fuel curves. These can be based on either intake airflow measured from a mass airflow sensor, or engine load information from a MAP sensor.

If there isn't a mass airflow sensor, then the ecm uses the engine rpm and MAP (manifold absolute pressure) sensor data to adjust injector pulse width.

3,000 rpm in neutral is very different from 3,000 rpm in gear, and requires much less fuel flow to hit 3,000 rpm in neutral. The engine will have a high manifold vacuum reading while revving in neutral, and the MAP sensor provides the data to help the ecm "see" this condition.

Sorry for the long winded version.......heres the short version......swap the MAP sensor from one motor to the other.
 
thanks. just need to know where to locate it. I think its under the intake, but I'm afraid to lift it due to the wires being restricted. I have looked under[lifted until felt resistance] and noted wires going to bottom.
 

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