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Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 10747
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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1993 mercury black max v6 replaced upper voltage regulator,

Customer Question

1993 mercury black max v6 replaced upper voltage regulator, had a total meltdown,driveway test with earmuffs seemed OK voltage on guage back to 13.8+\- tach now on line boat in water starts good idles well in gear no power, sounds like one bank of cylinders not firing,or timing not advancing,fuel delivery system OK,occasionally all cylinders fire,runs well,then cuts out,still propels boat through water,but no more than 1000rpm,after that it coughs runs rough, no increase in speed or power
Submitted: 2 years ago.
Category: Boat
Expert:  Jason replied 2 years ago.
Hello my name is ***** ***** I will be helping you today. The engine requires some diagnostics in order to figure out what the problem is with it. What kinds of questions did you have about it, and what were you looking to do here?
Customer: replied 2 years ago.
Get back to you later will have to do some tests with a meter,have many manual's
Expert:  Jason replied 2 years ago.
Okay just post back with any questions you may have and i'll be happy to help.
Customer: replied 2 years ago.
Tested stator OK trigger switch okvolage regulators okplugs and coils OK switch box stop circuit tests 900vdc at idle 1100 vdc at 1000 rpm think l need new switchboxes
Expert:  Tan replied 2 years ago.
The stator and trigger testing good leaves the switch box as the only thing left. There is no stest for the switch box you can only test the inputs. 7452A 3 Looks like you have it under control. Is there something you are concerned with?
Expert:  Tan replied 2 years ago.
Could I get the engine serial number please?
Customer: replied 2 years ago.
How could the voltage reading be so high
Customer: replied 2 years ago.
Expert:  Tan replied 2 years ago.
There is no spec for the stop circuit so I don't know what the voltage is actually reading. You are reading the voltage from the capacitor which is what gets grounded when you turn the key off unloading the capacitor. The capacitor voltage is extremely high.Out of curiosity how were you testing the stator and trigger?The part number for the switch box is 7778A12 Here is a link to the parts.
Expert:  Tan replied 2 years ago.
Here a link to other suppliers of the switch box.
Mercury recommends replacing both switch boxes.
Customer: replied 2 years ago.
Resistance test with an ohm meter
Expert:  Tan replied 2 years ago.
Ok. From what I read you have spark on 3 cylinders. So did you by chance swap the switch boxes around?
Customer: replied 2 years ago.
No all cylinders have strong spark and both boxes test the same
Expert:  Tan replied 2 years ago.
Have you checked the spark on all cylinders when the engine is acting up? This can be done with a timing light.
Customer: replied 2 years ago.
I did it on the ocean with insulated pliers all arced at least 2 inches from cap to plug
Expert:  Tan replied 2 years ago.
Does the engine drop rpms on each cylinder when you removed the plug wire. Now this engine has a low speed coil and a high speed coil. It can fire at low speed and not at high speed. Did you do that check when the engine was acting up?
Customer: replied 2 years ago.
Like l said on the ocean ,with the throttle in high rpm ,while faulting rpm would fall a bit ,all cylinders seem to be firing but not developing any power and using an extraordinary amount of fuel,not developing any power after 1100 rpm
Expert:  Tan replied 2 years ago.
Seem isn't very sure they are all firing. Either they are or they aren't. We have to check with a timing light to verify. If you are dropping cylinder the engine will be low on power.

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