8.8 Coolant Temperature Sensor
Install the temperature sensor in a water passage of the intake manifold. Most intake manifolds have a plug that can be
removed for installation of a temperature sensor. In addition, some cylinder heads have a plug that can be removed for
installation of a temperature sensor. DO NOT install the sensor in the thermostat housing. The sensor must be located so that it
is in contact with coolant on the lower side of the thermostat. If a location cannot be found, a metal tee fitting may be installed at
the boat’s temperature gauge sensor, if so equipped. Then the gauge and PRO-JECTION temperature sensor can be installed
into the tee fitting. DO NOT use any pipe sealer on the threads that may degrade or reduce the ground connection of the
sensor. Tighten the sensor to 15 ft./lbs. torque.
9.0 CLOSED LOOP INSTALLATION AND CONNECTION (OPTIONAL):
The digital ECU is designed to utilize a heated, three-wire oxygen sensor to operate the system in a closed loop mode. When
operating in a closed loop mode, the electronic control ECU utilizes a reference signal from the oxygen sensor to determine
whether the engine is running too rich or too lean. The ECU then adjusts the fuel delivery to maintain a stoichiometric fuel
delivery (14.7:1 Air / Fuel Ratio).
NOTE: The installation of an oxygen sensor will operate with the digital ECU. This requires use of the Holley Digital PRO-
JECTION 2D Closed Loop Kit for 1 and 2-Barrel Applications, P/N 534-54.
WARNING: If you are currently using a Holley analog closed loop kit, P/N 534-27, all electrical wiring connecting to
this kit must be removed and replaced with a new wiring harness, Holley P/N 534-56. Failure to replace
this wiring harness will result in improper fuel delivery and possible damage to ECU.
WARNING! Use only unleaded fuels when operating an oxygen sensor. Use of Leaded fuels will DESTROY the
oxygen sensor and will result in incorrect exhaust gas oxygen readings, which may cause poor
performance and cause serious engine damage.
WARNING! The use of some RTV Silicone sealant will destroy the oxygen sensor. Ensure that the RTV silicone
sealant that you use is compatible with oxygen sensor vehicles. To determine compatibility, check the
packaging of your RTV silicone or contact the sealant manufacturer.
WARNING! An experienced inboard mechanic should be used for installation of the oxygen sensor. Inboard engine
exhaust manifolds have water passages inside them for noise and cooling purposes. An improperly
drilled manifold will result in water getting into the oxygen sensor causing it to be destroyed and
destroying the exhaust manifold. The oxygen sensor should be installed as far from a water location as
possible and as close to an exhaust port as possible.
NOTE: The oxygen sensor, if used, should be installed by someone with experience with inboard boat engine exhaust systems.
Any competent inboard repair shop should be able to perform this task at a minimum cost.
Locate a position for the oxygen sensor as close to the engine as possible. Pick a location that allows easy installation and
removal of the oxygen sensor. Figures 7 & 8 show the location used by Holley engineers during development of the Marine
PRO-JECTION systems. The oxygen sensor was mounted in the exhaust port farthest from the water injection hose and riser
tube at the top of the picture. This location was chosen to prevent water that is pumped into the exhaust system from running
back down the riser tube and into the exhaust manifold. This can wet the oxygen sensor and cause damage to the oxygen
sensor. The close-up shows that the hole for the oxygen sensor was drilled through an area of the manifold that does not have
any water passages. This should be done to prevent any possibility of water leakage from the wet areas of the manifold to the
dry areas.
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