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Tan
Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 10666
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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1993 225 Johnson starts and runs normal how ever acts like

Customer Question

1993 225 Johnson starts and runs normal how ever acts like ignition is being switched on and off under load. Motor was running fine wot. Pulled back to idle. Problem started on next take off. I have unplugged shift switch, no change no warning lights or bells new champion plugs. Vro pump removed flywheel checked stator and magnets. I don't believe it is going into s.l.o.w. Only thing that might help past two years when using boat for the first time of the season. Cranked and cranked smelled fuel then bam fires up and runs perfect the rest of season. This year same issue. But know cutting out under load
Submitted: 1 year ago.
Category: Boat
Expert:  Tan replied 1 year ago.
Hello. My name is***** you have a timing light to check the spark under load? We need to use the timing light to see if we are loosing spark when the engine acts up. Connect the timing light to each cylinder and watch the flash of the timing light. The flash should be steady with no dead spots. Do this test on each cylinder. If you find a misfire swap that cylinders coil with a known good coil. Does the misfire stay or move. If the misfire moves that coil is bad replace. If the misfire stays we have another ignition component failing. When running the boat choke it when it acts up. Does engine run better? Squeeze the primer bulb when engine is acting up. Does engine run better. These 3 tests should tell us something. Post back with findings.
Customer: replied 1 year ago.
I own a auto repair shop and I have tried all the fuel related tests, it is not a miss it is just like I turned the key off and on Next trip out I will unplug all senders that affect s.l.o.w functions. Also will disconnect ign ground lead. I had a timing light last trip however engine bucking is so forceful I would not want to be hanging out on rear deck for this test. I will have to try to duplicate on trailer. Built a peak voltage adapter today tested stator, sensor coils all good. Cdi is original from 1993 (power pack). Thanks for your help so far
Expert:  Tan replied 1 year ago.
Yeah when it bucks and jerks that is an ignition misfire or the engine is jumping out of gear. The misfire is the most likely.Now the way I do this test is connect the timing light to # ***** cylinder run the boat. Watch the flash of the timing light. If the flash is steady then that cylinder is ok. Stop the boat move the light to the next cylinder go run the boat till it acts up watching the flash of the light. Do this on each cylinder. When you find a misfire swap that cylinders ignition coil with a known good firing coil. Repeat the test does the misfire move? If it moves that coil is bad. If it stays then we have another ignition component failing. Testing this way you aren't hanging over the boat when it is acting up. My timing light has leads long enough I am in the boat. Do you follow this procedure?
Customer: replied 1 year ago.
I understand an ignition miss this would cause poor power if one or two cylinders where dropping out this is not the case. I am sure I am loosening spark all 6 cylinders at same time. Under accel it will quit and throw you over helm , then back to normal thrown back to seat. Not fun !! As for gear box just completely rebuilt. Problem was there before hand. Two vro pumps one new on used. Fuel bulb good. It is like switching light on and off at rpm range 2000 to 5000 not consistent. Sorry I suspect we will get to bottom of this. I spoke to owner where I bought boat from he remembers same type of issues years prior but do not remember what caused this. Not this motor. To add I am original owner motor might have 250 hrs on it. I will indeed try timing light on trailer to confirm ign loss.
Expert:  Tan replied 1 year ago.
Ok the only thing that will an issue like this is a short to ground on the black/yellow wire or power pack failure. Disconnect the black/yellow wire from the power pack run the boat. You won't be able to turn the motor off as you have eliminated the stop circuit. This will leave the power pack as the only thing left to cause complete spark loss. Disconnecting the black/yellow from the pack eliminates the kill switch. key switch and the engine wiring harness. The only way the engine will loose complete spark loss is grounding the black/yellow wire other wise the engine will run till it runs out of gas. The stator won't do on off and neither will the timer base. So by the process of elimination the power pack is the issue if the black/yellow wire disconnections does stop the issue. Do you follow what I am saying? Do this test and post back with findings.
Customer: replied 1 year ago.
That's what I will do. I was also told by cdi to remove yellow stator wires and try. Keep you posted need some solid info for next step
Expert:  Tan replied 1 year ago.
Ok keep me posted.

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