0 psi water pressure but no guardian alarm

[silver_power]

Hello. I gave a 350 mag mpi s/n 1A348183 , MY 2010 with about 450hrs. I had some ignition issues but I now solved them. I just made a test run today to be sure that everything is OK but something strange happened. The engine works very good with smooth operation, the temp is steady at about 72oC but as I scrolled to the smarcraft readings, I saw 0 psi water pressure​​​​​. Obviously I have an issue with my impeller OR with my water pressure sensor. This us something that I can easily find , but my concern is why the engine guardian did not operate. No alarms, no beeps, and 0 psi water pressure!!. The temp was normal and steady. The reading was the same at all the range. The only thing I noticed was about 200-250rpm loss at wot with just a full tunen up engine. (New cap, rotor, wires, plugs all genuine) but this is something I do not concern,...maybe not so good gas. Do you have an idea why is this happening?
Thank you very much.

 

[alldodge]

I think everything is ok, because the flag is not checked (not turned on), or if your at idle this can still be ok. The older 555 ECM would set off the alarm all the time because of the water pressure sensor. The newer 555 PCM (don't have a manual for them) could have different settings.

Old was 1-5 at idle and 7-17 psi at WOT minimum. Being your using metric (bar) 1 psi is 0.0689 bar, so it has to come up some (15 psi) to show 1 bar. Your also don't have seapump CKT Hi or Lo

You open or closed cooled?

 

[silver_power]

So for the ecm there is no problem having 0psi of water pressure?. If this happens then there is no problem since the ecu does not limit the power.
Am I right? I had just a thought that maybe these 200-250 rpm loss was from the low water pressure reading.......I am going to change the impeller anyway, if the water pressure will not raise at the gauge, then it will be obvious that the sensor is faulty.

 

[QBhoy]

Sw pressure switch is one of about 4 or 5 common mpi known weak points. Simply replace it. All good.
Or, sometimes you can get away with cleaning it. I did. Often gathers sand and silt and gets blocked.

 

[alldodge]

So for the ecm there is no problem having 0psi of water pressure?. If this happens then there is no problem since the ecu does not limit the power.
Am I right?

My thought is that your using smartcraft with the metric system (Celsius and Bar). Don't know if there is any decimals seen or just a zero. You could shift from Metric to SAE and see if a psi reading is shown

If it still does not, then maybe the flag is turned OFF in the PCM

 

[silver_power]

I am open cooling system. The smarcraft has decimal even at metric system. It reads 0,00bar. Besides, before my previous sensor become faulty, it read 0,13bar at idle and about 0,75 at wot. My old genuine water pressure was stuck ed at 2,75bar and I used it the last summer period. I changed it with an aftermarket 30psi sensor and now it shows 0,00bar. Probably the sensor is not good. This is something I am not concerned since I have no alarms and my temp is OK. I will change is with the old one (stuck ed at 2,75bar). I will not buy another one genuine since it only leaves for about 3months. My question is the folowing. Is it possible the ecu to limit the power before it reads 0bar water pressure without trigger an alarm? The engine runs perfect till 4700rpm and the strange is that the throttle is not to wot. Let say it reaches 4700rps at 3/4 throttle and as I go to wot it does not raises rpm. ...The cables are OK since it fully open the throttle plate and the boat used to reached about 5000-5100rpms with the same prop and with bigger load. It has just the same attitude as an overpitzched prop. It only raises certain rpm and when you push it more it cannot raise the rpm.
No backfire, no surging, no alarms, very fast acceleration fast get on plane, very good consumption, new gas at portable tank....everything seems perfect. But low wot rpm about 200-300rpms...... If there is no possibility that the ecu limit the power without trigger an alarm, then maybe the gas is not very good......I can not imagine something else...I do not have something else to claim any problem...

 

[alldodge]

Thanks that helps me understand, what your seeing.

If yours was the older ECM I would say there would be an issue and a 2 beep alarm and reduction in power by 10% in most cases. Yours being the PCM I'm not as sure of the possibilities. If your getting your 2 beeps at start up says your alarm horn still works.

While this has no impact with the water pressure item, if the TPS does not go to 100% then the PCM does not know to give the motor more fuel. The TPS is moving full but maybe the internal workings just stopped short

At this point I would suggest have a scanner connected. The scanner can record all info as the motor goes through its operation

If you can see the TPS on smartcraft display, see what its showing.

 

[silver_power]

The TPS is working good because I tested with a voltage meter when I had a surging problem and I wanted to isolate the TPS a's the problem. It had steady linear ra using of voltage till the end. About 4,6v at wot.......

 

[silver_power]

Just a thought.....here in Greece we only have 95 , 97 , 100 octane gasoline. I usually use 95oct unleaded gas but now just for the test ride I put 97oct to the portable tank. Is it possibly the higher octane gas to make the motor have worse performance as higher octane gas is burned slower?

 

[alldodge]

Is it possibly the higher octane gas to make the motor have worse performance as higher octane gas is burned slower?

While it is possible but in most cases it usually just cost more. That said, the more ethanol gas contains the less power is produced.

 

[silver_power]

OK so it makes a little sense but for sure I will wait for the summer to solve my questions.....maybe it is the gas for not reach the usual wot rpms...
thank you very much

 

[alldodge]

Your welcome and sorry I couldn't be of more knowledgeable help. Would be great if maybe user muc might add his thoughts. If he doesn't show up, might send him a PM

 

[QBhoy]

Pretty sure it’s the SW pressure sensor. Also pretty sure mine didn’t beep when it failed, but put the engine into 90% power mode. I only discovered this after the vessel view device (smart craft) displayed a fault code...which with a little help from All dodge (I’m sure) managed to relate the code to the sw press sensor. It also triggered other sensors at the same time and intermittently.

 

[QBhoy]

Look at these fault codes from the manual. All SW sensor related and show intermittent guardian modes from varying to 90%. All exactly what I had.

 

[QBhoy]

This too.

 

[silver_power]

Thsee images are very useful but according to these I should have a horn/beep alarm and a bell index at my smarcraft gauge , but I do not have any of these. If I plug out the sensor,then a fault icon and a beep occurred immediately and so the beeper works. But the 0psi is not trigger any alarm and I do not know why. Is it possible that mercruiser has disable the alarm at 0psi reading IF the temperature reading is normal just like in my situation? I mean it will trigger an alarm only if the temperature is high.

 

[alldodge]

Looking at the pressure sensor for your motor is the same part as early model ECM. The failure modes are the same also as seen in QBhoy postings. So it leads me to believe this may be an internal issue to the PCM or the smartcraft monitor.

Wouldn't be the fist time that the computer doesn't see an issue, but info being sent to a display does not fully represent what is being read by sensors

 

[silver_power]

So if I understood correct, maybe there is an issue and ecm limits the power without triger an alarm?

 

[alldodge]

So if I understood correct, maybe there is an issue and ecm limits the power without triger an alarm?

Not sure that is correct. I'm saying that the PCM may think everything is fine, but the info sent to the display is the issue.

QBhoy has the newer manual and it to shows there are the same error codes and if the PCM did see this issue there would be a code set with power reduction and 2 beeps.

So the inability of the motor to achieve full RPM may not have anything to do with the low water pressure. If the PCM is causing the power reduction but not setting codes then this is a PCM issue.

Would be good if you could get the motor scanned