2003 350 MAG MPI ECM Heat

E

eric260

Member
Apr 15, 2021
72
Boat Info
2003 260 Sundancer
Engines
350 MPI
On my 2003 350 MAG MPI the previous owner had a spacer installed that sets it further off the engine. They also ran a duct, similar to the blower, and connected it to the outside source. Has no fan, just looks like a vent. Any idea why this would be done? Is this normal?
 
Not normal... must have assumed the ECM was failing because of heat.
 
Is that a real concern? I have an issue on another thread we’re the boat beeps, similar to when you turn on key, and rpms drop. Only happens after I’ve been running around for awhile. Makes me wonder if the ECM could actually be causing it
 
Going into alarm and dropping RPM's sounds like its going into "guardian" mode. This mode is to save the motor when harmful conditions exist... like overheat, low oil pressure, low water pressure, etc..
If heat causes the ECM to shutdown or malfunction, then it could be defective. It should be able to sit where it was designed.
 
eric260 said:
Is that a real concern? I have an issue on another thread we’re the boat beeps, similar to when you turn on key, and rpms drop. Only happens after I’ve been running around for awhile. Makes me wonder if the ECM could actually be causing it
Click to expand...

The ECM would be doing it if any of the attached critical sensors throws an alarm. The ECM does not know the difference between a failed sensor and a sensor doing its job. The best thing to do is pull any codes available from the ECM and track down the problem. Things like over temp, low water pressure, overspeed will cause the ECM to drop the engine into guardian mode to try to protect itself.

-Kevin
 
Electronics are funny - sometimes they act in ways that defy logic. Generally, they do just as Kevin said - they simply react to input (and interpret). Is the ECM the problem? Hard to say... could be,though... especially with that spacer as that was obviously done for a reason. The question is... was there an issue with it and was this the band-aid that a PO did? Or, did the PO replace an ECM and just decided to add the spacer with the new one "just in case".

Or, there's still that possiblity that we talked about before of wiring issues to/from the ECM (including grounds).
 
Last edited:
JimG said:
Going into alarm and dropping RPM's sounds like its going into "guardian" mode. This mode is to save the motor when harmful conditions exist... like overheat, low oil pressure, low water pressure, etc..
If heat causes the ECM to shutdown or malfunction, then it could be defective. It should be able to sit where it was designed.
Click to expand...
I had a tech hook up to ECM, no guardian mode. The “alarm” is exact same beep as when you turn key to start. He thinks something is tricking engine into thinking key turned on then off. Maybe ignition. However problem only happens after running around for about an hour or more. IE things have heated up
 
KevinC said:
The ECM would be doing it if any of the attached critical sensors throws an alarm. The ECM does not know the difference between a failed sensor and a sensor doing its job. The best thing to do is pull any codes available from the ECM and track down the problem. Things like over temp, low water pressure, overspeed will cause the ECM to drop the engine into guardian mode to try to protect itself.

-Kevin
Click to expand...
No codes when checked by mercruiser tech
 
Lazy Daze said:
Electronics are funny - sometimes they act in ways that defy logic. Generally, they do just as Kevin said - they simply react to input (and interpret). Is the ECM the problem? Hard to say... could be,though... especially with that spacer as that was obviously done for a reason. The question is... was there an issue with it and was this the band-aid that a PO did? Or, did the PO replace an ECM and just decided to add the spacer with the new one "just in case".

Or, there's still that possiblity that we talked about before of wiring issues to/from the ECM (including grounds).
Click to expand...
Going with ignition switch first and crossing fingers!
 
Sounds more like a loose connection. Check your cannon plug and ground wire from battery to engine block
 
eric260 said:
Which one is the cannon plug?
Click to expand...
Search online Mercruiser cannon plug connector or the plug will look like the bottom half of this,Wiring Harnesses : ebasicpower.com, Marine Engine Parts | Fishing Tackle | Basic Power Industries
MER84-866337T01.jpg


What is your engine serial number? And Stern drive model? You may have fallen in with this past issue on page 3 of 3 if you have an Alpha stern drive, Boatinfo - Bulletins for marine engines and boat related accessories!
 
I had a similar situation with my last boat ending up with a failed ECM turns out small engine bay with twin engines just too much heat soak. The remedy was to run the blowers all the time the engines were running and for a few minutes after shut down. This solved my problem hopefully it's all you need to do? Blowers are designed to run continuously anyway.
 
Brite Idea said:
I had a similar situation with my last boat ending up with a failed ECM turns out small engine bay with twin engines just too much heat soak. The remedy was to run the blowers all the time the engines were running and for a few minutes after shut down. This solved my problem hopefully it's all you need to do? Blowers are designed to run continuously anyway.
Click to expand...
I very much think this is the case. I only have one engine, but it’s been running slightly hot due to low flow. I need to address that. But, whoever had it before thought to put a spacer under ECM and put air vent line right on it. Also, the problem never happens when we are doing 5 mph cruise. But it starts once I’ve done a long higher speed run, then I slow down. Once it starts, it keeps going, but I did not think to start running blower. Thank you for input
 
Brite Idea said:
I had a similar situation with my last boat ending up with a failed ECM turns out small engine bay with twin engines just too much heat soak. The remedy was to run the blowers all the time the engines were running and for a few minutes after shut down. This solved my problem hopefully it's all you need to do? Blowers are designed to run continuously anyway.
Click to expand...
Also, did it act up, and you did not address (by running blower) and it failed? Then you replaced and always kept compartment cool to keep new one from failing? Can you give me the details of your experience? Thanks
 
Maybe this has more to do with clogged risers or other cooling system issues causing a high heat condition near the ECM.

Addressing those issues may solve this one as well.
 
My situation was a frustrating one because it was intermittent at first but gradually got worse over the season. The second season it finally failed after going thru coil, pickup coil and head scratching. The mechanic I use was the one who said run the blowers all the time because everything in there is hot! I owned the boat for another ten years and never had a problem. The 2000 270 Sundancer with twin V6's is tight and hot. I'd change manifolds and risers every five years like clock work so I never had that problem.
 
Espos4 said:
Maybe this has more to do with clogged risers or other cooling system issues causing a high heat condition near the ECM.

Addressing those issues may solve this one as well.
Click to expand...
Well I already know I have some what if a cooling issue. But runs closer to 180 under full power. When I tried to get codes pulled, the tech said the water pump was pushing a low psi under power, only about 1.7. He said I should be closer to 3. So new impeller going in as soon as I have time. The hope is if I can get to running at proper temp, compartment stays cooler overall and finicky ECM works
 
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