Raw water water pressure sensor issue on Mercruiser 8.1

P

PSNI

Member
Aug 2, 2017
60
Boat Info
2000 380
Engines
Mercruiser 8.1 MAG (2005)
Mechanic replaced raw water impellers and belts over the winter while boat was winterized.

Engines fired up and water flow is good.

However, I'm getting the following Smartcraft alarm: STBD Fault 36. Sea pump CKT High. I get this alarm if the engine is running or not. And the starboard water PSI shows 43.4 PSI with the engine off and when running at idle and up to 1500 RPM.

Mechanic would be happy to scan it.

I cannot locate the sensor to remove and inspect it. Can someone tell me where to find it?

This is a 2000 DA with 2005 8.1 inboards.

Thanks, Peter
 
Sensor problem is possible, might also be a wiring/connector plug.
Possible that it defaults to a high value if wire/plug is not connected?

In any case, on my 2002 with 8.1s, the sensor is just off the outlet side of the raw water pump. It’s a bear to get to, but doable.

Good luck,
Rob

oh, and I believe it takes a 1” socket
 
Thanks Rob. I was wondering if he left it disconnected. Or connected incorrectly. I can't find anything that tells what that reading would be. I believe the range is 0-100. So maybe no voltage is read in the middle. And 43.4 is above the threshold for too high.

I obtained this diagram for my serial number range from the Mercruiser parts catalog. The sensor is # 13. It's appears to be right next to the blue drain plug. I'll bring my mirror with me next time I check.
 

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PSNI said:
Thanks Rob. I was wondering if he left it disconnected. Or connected incorrectly. I can't find anything that tells what that reading would be. I believe the range is 0-100. So maybe no voltage is read in the middle. And 43.4 is above the threshold for too

I obtained this diagram for my serial number range from the Mercruiser parts catalog. The sensor is # 13. It's appears to be right next to the blue drain plug. I'll bring my mirror with me next time I check.
Click to expand...

When my sensor failed, I got a VesselView code that said “sensor fail.” So I’m purely speculating on the possibility of what a disconnect might look like.

Your diagram matches my setup exactly.
If you get to the point of removing the sensor, I found it easier if I removed the fuel/water filter first.

Rob
 
If you can reach it, you might try reseating the connector a couple of times, sometimes the can be a little corrosion on the pins. Then check to see what the PSI is before starting the motor. I have one that reads about 7psi before I start it. Needs replacing.
 
I’ve reseated the connector. I’m still getting the same reading. 43.4 with the engine off. I disconnected the connector. Still the same reading. Does the connector go back to individual interface on a controller.? If anyone has a wiring diagram please share.
 
I found a manual excerpt that indicted the 43.4 PSI is the "default" reading which I took to mean that it will read that when getting no voltage reading.

So I cleaned the contacts on the cable which appear to be oxidized and the problem cleared.
SW Pump .jpg
 
Thank you for the help gentlemen. I do have one more question.

Do I need to be concerned about "clearing codes"? Does a code need to be cleared by a scan tool to take the engine out guardian mode? I was able to cruise at 3400 RPM yesterday. And there are no active alarms in Smart Craft.

Thank you.
 
So I found a PCM manual I can only read it online. It says the CKT HI code indicates it's seeing 5V from the sensor. I would have thought it would have seen 0V if the connector was corroded.

upload_2020-5-11_10-54-50.png
 
I think I understand. An open circuit would be 5 volts.

upload_2020-5-11_11-25-5.png
 

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It provides excellent, detailed information on fault conditions and codes. Sticky codes! Go figure.

FAULT CONDITIONS
Most faults can be detected with the engine running, or with the key on and engine off.
However, some faults require the presence of engine RPM, and cannot be detected with
the key on but the engine off. Examples of this type of fault are EST (cylinders 1 through
8) shorted circuit and all injector faults (fuel and direct).
Some faults are only detected with the key on and engine off. Examples of the type of fault
are EST (cylinders 1 through 8) open circuit.
In addition, some faults are programmed to ignore certain engine speeds. For example,
the low block pressure sensor fault (sea pump pressure on a MerCruiser sterndrive) is
typically not enabled until enough load has been achieved to develop a reasonable amount
of water pressure. Therefore, this fault will not be set at idle.
Faults also take a certain time to set. The time it takes to set a fault varies greatly and can
also vary with engine RPM. Faults generally set faster at higher engine speed.
STICKY AND NON-STICKY FAULTS
All faults are classified as either sticky or non‑sticky. Sticky means that the fault, once set,
will continue to show up as active, even if the circuit or problem has corrected itself. A key
switch cycle is required to reset a sticky fault.
A non‑sticky fault is a fault that will change its status from active to inactive without requiring
a key switch cycle.
The CDS diagnostic tool will continue to display a sticky fault as active even though the
cause of the fault has been corrected. Cycle the key to reset all faults if there is difficulty
correcting a fault.
DEFAULT SENSOR VALUES
Default sensor values are preprogrammed amounts used by the PCM to calculate fuel and
ignition values, when the sensor in question has exceeded its preprogrammed diagnostic
limits. Default sensor values typically are used when the sensor has a circuit high or circuit
low fault.
Most temperature sensors default to 0 °C (32 °F). This can be verified by unplugging the
sensor in question and watching the data stream value with the CDS.
Most pressure sensors default to a preprogrammed number also. MAP sensors usually
default to 70 kPa (20.7 in. Hg). This can be verified by unplugging the sensor in question
and watching the data stream value. Other pressure sensors will have their own default
values which may be determined as described previously.​
 
I know this is a pretty old post but I’m getting the 43.4 psi reading from my starboard water pressure. I understand I should start by cleaning the contacts. This sounds silly but I cannot reach the darm plug. Any advice on the 8.1s v drive and reaching that connector?
 
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