Will bad trim sensors trigger guardian mode?

Sandman251

New Member
Dec 12, 2021
1
Boat Info
1997 270 sumdancer
Engines
7.4 mpi
Hello all. Brand new Forum member but longtime Sea Ray owner. Looked at an 02 bowrider with a 5.0 MPI. Owner said boat runs great except for it "cuts out" at around 4K RPMs. Boat sat for around two years now he wants to sell it. He replaced the sensors and claims it has fixed the problem primarily because the trim gauge now works when it didn't before. I didn't think bad trim sensors put the boat into limp mode. The boat will start right up and idles nicely on muffs. The boat is in pretty rough shape but has potential. Won't be available for a sea trial. Any ideas?
 
Welcome. I would look at seawater press being the more likely issue. Check the Impeller or sensor. It sounds like low seawater press at revs to me. Will seem to run fine at idle, but the guardian is protecting the engine when you hit the 4k area.
BTW, unless you are getting this boat for an absolute steal, I would stay away from it, it sounds like it has been neglected, could be a giant headache.
 
I doubt that boat has a water pressure sensor or the ability to go into limp mode. Sounds like it's running out of fuel.
 
Is this an EFI engine? If so, it should have smartcraft technology which includes a host of sensors that can limit power BUT there should then be a corresponding double beep alarm or even a solid horn alarm unless it’s been disconnected.
 
Early EFI and MPI used the mefi 3 ecm. So very basic system, no double beeping, no limp mode. Wasn't until they started to use the 555 ecm that uses that technology
 
We had an 02 28p with 496. I had a water temp sensor go bad and that triggered guardian mode. But it gave off an overheating error message although the engine was obviously not overheating. Boat ran fine in limp mode.
 
Big blocks have a PCM which has more capabilities than his small block ECM of that age.
 
You know CharlieG had the same year & size engines in his 280 SS and had a similar problem on one of his engines: fine operation on the low end and then it would die when he dropped the throttle. As I recall the problem was because flapper back flow preventer valves rotted out and the debris dropped down into the y pipe causing a partial blockage. He went through the whole litany of sensors swaps, fuel system pressure checks, etc.

We’ve assumed it’s going into Guardian Mode, but the info is third hand from the previous owner, “cuts out” could describe a partial exhaust blockage.
 
Transition from MEFI-3 to 555 is a little tricky. "5.7's" were never made as an MPI, only EFI. However, when designated as a "350MAG", they WERE MPI -- but only after (and this gets to Scof's point) a certain date were they MEFI-3 - before that they were MEFI-3. 5.0's were made in both combinations. Now, when the 5.0L became an MPI (no longer an EFI) around 2001/2, the 5.7EFI was dropped from the lineup since the 5.0MPI produced the same HP as the 5.7EFI.

So... while a 350 could be either MEFI-3 or 555, a 5.0L MPI could ONLY be 555. The same would hold true, by the way, for a 4.3L MPI - only 555... if it's a 4.3L EFI, that would be MEFI-3.

Which means... the OP's engine, a 5.0L MPI, WOULD use the 555. The MEFI-3 "could" reduce power based on a few inputs, but the 555 monitored more things and reduced power in "steps" instead of all at once.

All this said... we may be talking to ourselves here...
 
Transition from MEFI-3 to 555 is a little tricky. "5.7's" were never made as an MPI, only EFI. However, when designated as a "350MAG", they WERE MPI -- but only after (and this gets to Scof's point) a certain date were they MEFI-3 - before that they were MEFI-3. 5.0's were made in both combinations. Now, when the 5.0L became an MPI (no longer an EFI) around 2001/2, the 5.7EFI was dropped from the lineup since the 5.0MPI produced the same HP as the 5.7EFI.

So... while a 350 could be either MEFI-3 or 555, a 5.0L MPI could ONLY be 555. The same would hold true, by the way, for a 4.3L MPI - only 555... if it's a 4.3L EFI, that would be MEFI-3.

Which means... the OP's engine, a 5.0L MPI, WOULD use the 555. The MEFI-3 "could" reduce power based on a few inputs, but the 555 monitored more things and reduced power in "steps" instead of all at once.

All this said... we may be talking to ourselves here...
Very good info Lazy, Do you know if in any of the systems you mention, the trim sensor would reduce power? Doesn't seem likely, but I don't positively have the answer.
 
Very good info Lazy, Do you know if in any of the systems you mention, the trim sensor would reduce power? Doesn't seem likely, but I don't positively have the answer.
If it does, it would surprise me. Offhand, I don't know for sure - but I just can't imagine why that sensor would activate the Guardian mode.
 
I have a 2003 6.2L, my cool fuel started failing which made the boat behave like it was in guardian mode. There are 2 fuel pumps, the booster can keep you running so you don’t get the beeps but can’t get over about 2000 rpm. It’s a tough fix because the cool fuel is on the bottom of the engine.
 

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