Mercruiser issues with alarm and guardian mode

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NH Tooner

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I have a 2007 Mercruiser 496 8.1 with bravo 3 and has 130 hours. Also has a closed cooling system. I have issues with the alarm going off and then going into guardian mode at about 3000 rpm

Took it to the dealer for a scan and they said it was temp related. It does not overheat. I changed the thermostat. I changed the seawater impeller and housing as recommended. still the same.
Then I changed the exhaust manafolds and the 2 temp sensors. Also changed the water pressure sensor. Still acts exactly the same. Changed the oil and filter and fuel filter also. Motor runs great until 3000 rpm.
What else can make that alarm go off?
Thanks for any help
 

wellcraft-classic210

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I did hear of someone with a restriction in a check valve that sent most of the water to the manifolds & starved the engine. He was getting an overheated engine that was visible on the gauges & an alarm due to lack of flow & associated heat. I mention this as apparently the check valve is not shown in all diagrams -- But again the gauges should show a temp rise at times if that's the issue.
 

scoflaw

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Have you ohmed the CTS ? Might be sending a false reading to the ECU about the overheat
 

NH Tooner

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I did hear of someone with a restriction in a check valve that sent most of the water to the manifolds & starved the engine. He was getting an overheated engine that was visible on the gauges & an alarm due to lack of flow & associated heat. I mention this as apparently the check valve is not shown in all diagrams -- But again the gauges should show a temp rise at times if that's the issue.

I inspected the check valves when I had the manafolds off. They looked good.

I am not having a overheat issue and the manafolds are cool to the touch.
 

NH Tooner

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Have you ohmed the CTS ? Might be sending a false reading to the ECU about the overheat
No I did not. I will change that sensor and see. What other sensors might trigger the alarm? I feel like changing them all. My thought are a bad sensor somewhere.
 

alldodge

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Took it to the dealer for a scan and they said it was temp related. It does not overheat.

Without an actual code being thrown (no mention of code from dealer) I'm skeptical that its temp related. Being close to 3K rpms the ECM may think your not in gear. Look on the shift plate and see if you have the gear switch in the pic

shift plate switches.jpg
 

scoflaw

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Your dealer said it was temp related. You should find out what he saw to make that statement. That ECM will store codes, and you need the scanner for more info. You will be able to monitor the temp on the tool and compare it to your gauge or an IR gun.
 

NH Tooner

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Your dealer said it was temp related. You should find out what he saw to make that statement. That ECM will store codes, and you need the scanner for more info. You will be able to monitor the temp on the tool and compare it to your gauge or an IR gun.

He just told me to change the impeller and housing then go from there.
 

NH Tooner

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so I changed the CTS and temp gauge sender. Same results. I put an IR gun on the manafolds 137 degrees on the manafolds and 150 on the elbows @ 3200 rpm on muffs and in gear.

I will test that shift switch. I think Im going to buy a scanner Any recommendations on that?
 

scoflaw

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I have that 2nd tool in AD's link. Not the best IMHO. Should be good enough to figure out your problem though. Make sure you get it with the 555 adapter you'll need.
 

NH Tooner

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Ok I purchased a Techmate Pro scanner. played with it for awhile. wasn't giving me any worthwhile info.. I few minor faults that have nothing to do with my motor. I cleared all faults and run the motor. 2800 rpm in gear. all good. manifold temp is about 10 degrees hotter on port than starboard. Reved to 3300 to get an alarm and to go into guardian mode. now gives a fault seapump block/low pressure. I already changed that sensor so might be something in the line. Maybe the checkvalve in the manafolds are bad? Anyway I think I'm going to take all the lines off and clean/ check everything from inlet to outlet. and change those check valves. Any other suggestions? scanner is awesome by the way!!!
 

scoflaw

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Have heard some of those water pressure sensors have a grounding issue, and some run a dedicated ground to it. If you don't have an overheat issue, doubt you'll find a blockage.

Definitely a known Smartcraft problem.
 

NH Tooner

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Have heard some of those water pressure sensors have a grounding issue, and some run a dedicated ground to it. If you don't have an overheat issue, doubt you'll find a blockage.

Definitely a known Smartcraft problem.

so you say run a ground wire to the brass part of the sensor?
 

scoflaw

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Worth a shot. Been a documented issue.

​BT probably knows how to override the sensor
 

alldodge

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So far no one has figured out how to bypass the sensor. As for the ground issue, just make sure to use no sealant on the threads. Also since the sensor is mounted on the power steering cooler, make sure the bolts holding it to the engine are tight and the cooler does not move any.

Low pressure can also be from anything clogging up the channels, this is from the drive, thru the pump and out. My first thought is the seawater pump. Even though the impeller has been changed those pumps have issues with sucking air if the wear plates are not in good shape. You could get a piece of 1 1/4 clear hose and put it inline to see if anything is showing up
 
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