Mercruiser 5.7 engine dies; No power to panel

[Rich2261]

Been lurking here since early July, and it is a terrific resource but haven't been able to solve my issue yet. My set up is: Mercruiser 5.7; TBV; 2 BRL; Eng S/N: 0M326453; Bravo1. Simple reliable engine, until this year.

Problem:

• Engine starts fine, couple of pumps to prime and kicks right over;
• Runs 5 to at most 15 minutes, then dies;
• No warning horns sound;
• Loss of electric to the panel/ignition, but blower and trim have power;
• Wait ~5 to 10 minutes, then power comes back to the ignition/dash and can re-start but will die again, usually sooner than the first time, also with no warning;
• Power comes back to the panel without re-setting any circuit breakers or fuses or any other action by me;
• Happens when idling, tied up at dock;
• Happens under load/underway;
• Idle RPM’s had been ~700 and sometimes still is, but sometimes tach is reading >1200 at idle on throttle, tho not sure if that is a tach error or the engine is spinning that fast;
• IR thermometer shows risers at ~125F port and ~160F starboard, which checks with mercruisers guide

Went at this as electrical problem and have tried so far to fix the problem without success:

• Put new battery in (old one was at 11.6v – thought this might be source of issue, but it wasn’t) Now at 12.6;
• Checked Alternator with VOM and was in Clymer spec;
• VOM shows current both sides of 50 amp CB

• Tightened loose negative battery cable clamp with new bolt to replace old rusty one that wouldn’t tighten;
• Swapped new ignition switch in (old one had worked loose in dash and was twisting). Have correct voltage at ignition;
• Replaced 50 amp circuit breaker, with part # Mercruiser New OEM 50 Amp Circuit Breaker 88-806950, 88-11178A01
• Replaced ignition coil with quicksilver #8M0079202 COIL KIT-IGNITION. Old coil was greasy;
• Wire harness – opened and looked clean so re-attached;
• As much as I can see, do not spot any frayed/worn wires
• Have not added any accessories since buying boat new in '02 (Crownline 230BR)

Boat has not had fuel pump or gas line work and running then dying which with ethanol in midwest would make me think fuel system is problem, but why is power to the ignition lost if this isn't electrical? Any help or suggestions really appreciated here.
Thanks.

 

[Rich2261]

Gauges all read dead center while engine running. 170F; 13V; 40 oil.

 

[alldodge]

Howdy
Have you placed the meter on the Red/Purple wire attached to 50 amp breaker after it dies? Want to know if it kicks out and resets when it cools down

If that checks out place meter on Red/Purple on the key switch

 

[Rich2261]

Haven’t done that when it dies. Does the 50 CB re-set itself? Had one source say that you had to push the red button to re-set. Can test this but it will likely be weekend to do it. Thank you.

 

[alldodge]

Haven’t done that when it dies. Does the 50 CB re-set itself? Had one source say that you had to push the red button to re-set. Can test this but it will likely be weekend to do it. Thank you.

Normally I would expect to have to press, but its a simple check just in case

I sounds like your loosing all power, and if its there at the breaker and not at the key, then the motor connector would be next look