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Mercruiser water pressure sensor

S

sr2

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Hi guys. I have a Carver 2500 that runs a MAP/MPI 350 with a Bravo 3 leg. The motor is has low hours on it and is well maintained. I’ve had my 2nd water pressure sensor failure in two years, I’m over it and want to disable it for once and for good! I'm well aware of what it does and being compulsive oil press/water temp gauge watcher I'm happy to do without it. Can I fool the ecu with a resistor or do I need to have it disabled via the software?
 
The resistor route would be an easier task. The factory manuals are a little thin on the details of the sensors...one of the original books has some specifics and they sugggest a 75K ohm potentiometer would be a good starting place.

The only hiccup I see would occur if the guardian strategy looks for specific thresholds of seawater pressure vs RPM...if that's the case, something like a PIC controller circuit should be able to function as a surrogate sensor...
 
Would be nice if someone could figure this one out, over at iBoats we have had many discussions on the topic. We never were able to verify what the exact specs of the sensor, only the type. It appears the main problem is most likely the range of the sensor, as in 0-145 psi. With this kind of range and it working in the 0-20 range it doesn't last, and salt water makes it worst

Pressure Sensor.jpg
Pressure Sensor chart.jpg


I would think a voltage divider circuit would do it. Could set one up with maybe a 1K resistor then a 0-2K variable resistor (pot). Adjust it so PCM see's 10 psi. Measure resistance of the pot then change pot for fixed resistor
 
why dont you just buy a sensor from a automobile, they are a 3rd of the cost and change it out each year as a maintenance item
 
Hi guys, I've finally found the info.
PinWire ColorFunction
Pin 1BlueSignal – sends pressure status to gauge/ECM
Pin 2Black/PinkPower/Reference – provides 5 V supply from ECM/gauge
Pin 3BlackGround – chassis or ECM ground reference
 

Typical Signal Voltage Range:​


  • 0.5 V or lower = Low or no pressure
  • 2.5–3.5 V = Normal operating pressure (depends on RPM and engine load)
  • 4.5–5 V = High pressure (or potentially a faulty sensor/wiring)

I'll use two same resistors in series as a voltage divider between the ground and 5V supply and take a tap from the connection of the two resistors to get a 2.5V signal.
 
Looks good but think about not "just" any 2 of same resistors.
Don't know if 200 ohm, 2K ohms, or 20K ohms will be needed. It all depends with amount of current and impedance
 
The input impedance of the ADC inside the Ecu is typically high to not load the sensor...the key is the current sourced to the 5Vdc reference...most are good for at least 20ma. I would start with a pair of 4.7Kohm resistors...
 
I'll use 2x 1.5K ohm .5 watt resistors. (could even possibly go down to .25 watt as it's a signal but playing it safe).
V out = ( R2 x V in ) / ( R1 + R2 ).
 
the +5VDC reference, from the ECU, will source 500ma....but there are multiple sensors sharing that source...I think the 1500 ohm parts will work.
 
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