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Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 10964
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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Tan I have dealt with you in the past and you seem to be

Customer Question

Hi tan I have dealt with you in the past and you seem to be the most experienced marine mechanic. I have a 2 stroke oil injected 175 hp carburetor mercury outboard from 1995. I have been having intermittent trouble with power at high rpms where you can here them drop and raise by a little bit but it use to go away. I also recently had trouble with continuous beep beep beep from the oil warning module but it was also in termite and the oil injection appears to be working as I have been using the motor alot still. Today the beeping came on and we lost significant power while in the middle of a trip and could not get back on plane. I'm thinking we lost some spark plugs or ignition coils. I'm on a 2 day fishing trip but just got to shore and have a multimeter. Can you help me figure out what to do.
Greg Joram
Submitted: 2 years ago.
Category: Boat
Customer: replied 2 years ago.
model number is ***** I have a multimeter and 300 piece tool set with me but would appreciate if I could receive help asap.
Expert:  Tan replied 2 years ago.
Hello Greg. The easiest way to see if you have lost spark is to start the engine then pull each plug wire off at the spark plug. The engine should drop rpms. If you find a misfire then swap that cylinder coil with a known good firing coil. Does the misfire move or stay. If it moves that coil is bad replace the coil. If it stays we have to do some testing with the ohm meter. Do these checks and post back with findings.
Customer: replied 2 years ago.
I pulled all the spark plugs while running at idle. Starboard 3 cylinders fire and change or stall engine and shock me when removed from engine running at idle. I can remove all three port plugs and get no shock and they do not affect engine idle. I have been having rough idle for the past 2 years and have been hearing slight change in rpm at high rpms in the past year but it was intermittent
Expert:  Tan replied 2 years ago.
Ok chances are we have a bad switch box. But lets verify with some tests. We can do this 2 ways you can swap the switch boxes or we can do some ohm tests. The ohm test will involve removing the blue and red wires from the switch box that has no spark. Test each blue to ground and each red to ground. You can do both switch boxes or just the one that is not firing. Blue to ground 3200-4200 ohms then red to ground 90-140 ohms. These are the charge coils one for low speed blue and the other for high speed red.
Expert:  Tan replied 2 years ago.
Here is the trigger test. The area circled in blus is the test you want to perform. If either of these fail the test that is the bad component. Now if both pass stator and trigger then you have a bad switch box. Mercury recommends replacing both boxes.There is no test for the switch box so we can only test inputs to the switch box.Post back if you need part number for any of these compnents. The switch box 778A1.
Expert:  Tan replied 2 years ago.
Here is the trigger part number. 96455A 9 and the stator 9619A19.
Here is a link to switch box.
Here the link to the stator # ***** and trigger # *****
Customer: replied 2 years ago.
Hey Tan I wanted to reply before to confirm my findings before I bought the stator but it was trying to charge me more money and I was on the water with only my phone. What happened to paying at the end. I always tipped you well and I do not like the way the service was set trying to charge me another $60 for 10 more minutes. So my red to ground was in spec but my blue to ground was reading only one OHM. So I bought the new stator, installed it after busting my bearing puller and buying a new one. Same issue only with the three port coils not sparking. What do I do now and is my old stator still good to sell on ebay?
Expert:  Tan replied 2 years ago.
Sorry but I have nothing to do with billing. I can send you to customer service after we have finished. If I send you now we won't be able to communicate.
Now if the stator failed the ohm test it is bad. Now we could have a bad switch box. Did you test the trigger? It isn't unusual to have more than one component to fail on a system of this age.
What you can do is switch the switch boxes does the misfire move when you switch the boxes?
Customer: replied 2 years ago.
I will have to perform the other tests. I had figured since I had found the fault in the stator that this was the issue. it also made sense because i wasnt getting spark at low RPM and that was the box that was out of spec according to that chart. I could have not been getting spark at all rpms though.To switch the switch boxes do i simply switch the red and blue wires with the red/white and blue/white wires?
Expert:  Tan replied 2 years ago.
Correct unless we have a trigger issue. So do the ohm test on the trigger first. Then swap the reds and blues.
Customer: replied 2 years ago.
Hey tan so i did all of the tests. The trigger resistances all meet spec. I tests the restances on my new stator(i got the CDI version as I read it was better than the OEM) im ever so slightly out of spec with 33.4 ohms on the red(does this mean a poor connection or should i be fine. Also my blue is still giving me funky readings on the new stator about a random number for a second when i have the ohm meter set for 2000, but a steady reading of like 2.8 ohms when i have it set to 20K ohms.I switched the red and blue leads from one switch box to the other and vice versa. the no spark situation stays on the same side. It sound to me like my original stator works and I need to two new switch boxes. Can you confirm and is there anything else I should test?Also does it matter if i keep the red and the blue wires where they are now or do I need to move them back to the original spots?Thanks
Customer: replied 2 years ago.
I'm also a real budget kind of guy that doesnt replace all the O2 sensors in his vehicle when one fails and I kind of replace them as they go. Can I get away with buying just one box or do I need to buy both?
Expert:  Tan replied 2 years ago.
You can buy just the one box. Since changing the stator leads didn't change the misfire that does point to the switch box. It isn't very likely that you would loose spark on 3 cylinder and even less likely on the same side. So we know the stator is good and the trigger passes the ohm test leaving the switch box as the only possibility.

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