merc. 20hp no spark.

[farscapehw]

i bought this 75' model mercury 200 with front of boat controls a year ago this month.

serial # 4148481

when i bought it it had a bad coil for the lower cylinder. it also had a fairly new switchbox on it.( november of 2004 punched out on the mfg date) i put a new coil on it and it ran like new for a few months. it started running bad missfiring and stuff. i ran it like that for a couple days because we were in the middle of a fishing trip. on the third day it quit running alltogather. i checked the spark and it had a very small amount on both coils but it was not consistant. so it set up for a while. i got my multimeter out today and tried to figure out what is wrong.

im an auto mechanic not a marine mechanic. but here is what i did.

i cut the wire going to the killswitch to the switchbox and it still wouldnt spark. i then checked the voltage of the wires to the coils from the switchbox, it was 0 volts. i checked and replaced all wires that were bare or old looking and still no fire. all my grounds apear to be good.

bare with me here, i dont know what these things are called...

under the flywheel there are 2 coils of which im guessing are the magnetos or generators, and a flat black thing with 2 wires going to the switchbox and 2 wires going into the coil looking things. i turned the key on in the running position but not starting and had 0.08 volts dc. i started cranking the engine and the voltage went up ranging between 11 and 15 volts. it was the same for both wires.

now im stumped and cant afford to go dumping money into this motor without knowing whats really wrong with it. can someone help me figure out what is wrong?

the part number on the switchbox is 114-4911 from cdi

 

[farscapehw]

Re: merc. 20hp no spark.

anyone?

 

[mmf]

Re: merc. 20hp no spark.

first off is there is no electrical connection between the battery and your ignition except NEGATIVE common. You ignition is self powered, hook any thing up to 12VDC and you have blown your powerpack instantly.

The two coils you see under the flywheel are a high and a low speed coils.
To check the coils by comparing resistance, the coil with the red and yellow wires should check around 320-550 ohms, the coil with the blue and yellow wires should measure around 3600-5500 ohms.

The blue and yellow coil generally put out around 180V running.
The red and yellow wire coil is 25V or more, running.

the black flat thing you refer to is a trigger for the switchbox. It's resistance is around 750-1400 ohms. It produces the 0.5V necessary to fire the SCR's in the switchbox.

 

[farscapehw]

Re: merc. 20hp no spark.

thank you. ill go test that now.

 

[Laddies]

Re: merc. 20hp no spark.

 

[farscapehw]

Re: merc. 20hp no spark.

ok sorry i havnt responded sooner, ive been very busy.

ok dont laugh at me, but when i went outside to test the stator and trigger i noticed that the positive and negative wires were reversed on the battery... lol.

now i have spark but its very very weak on both cylinders, touching the plug wire to my finger gives me a small shock to my finger but not much. its about a millimeter of arch to the chasis and isnt even enough to light up my light on my inline spark tester.

should i still test the stator and trigger wires? and how do i do it without removing the flywheel to get to the wires? (they are next to impossible to get to with the flywheel on and i dont have a puller that will remove it) also do i disconnect the wires from the trigger to the switchbox before testing it?

one more thing, my multimeter is saying both the + and - wires on both coils are - . im only getting a reading at all testing one lead on the main + cable and the other to the wires on the coils, and its saying 12.3 volts while spinning the engine over. i get no voltage at all when testing from ground to the coils wires. i dont know if thats normal.

 

[Laddies]

Re: merc. 20hp no spark.

You need to do the ign test as your engine has no charging circurt on it and no rectifier. The barrery is not wired into the ign. system so reversed polarity don't have anything to do with the problem.

 

[farscapehw]

Re: merc. 20hp no spark.

ok i could not disconnect the switchbox from the high and low speed coils to test them because i cant pull the flywheel to get to them i hope it doesnt throw off my test.

blue wire: 6.28 on 20k ohm setting
red wire: 6.46 on 20k ohm setting

brown to white on trigger: .786 on 2k ohm setting

question, when i test the voltage for the high and low speed coils, do i need to disconnect the blue and red wires from the switchbox? and just the starter spinning the engine over will produce the voltage in that chart?

 

[Laddies]

Re: merc. 20hp no spark.

Yes, they must be unplugged

 

[farscapehw]

Re: merc. 20hp no spark.

ok i got someone here helping me read the meter and stuff. i cut the wires off the back of the switchbox to test them.

blue wire: 6280 ohms, 140 volts
red wire: 6460 ohms, 120 volts
brown to white: 175 ohms, .5 volts

voltage i tested while engine was spinning over
resistance i tested without spinning engine over

he had the idea of doing a "touch test".... i dont like this test but it told us something.

the red and blue wires shocked the **** outa me, the blue wire shocked the horse **** outa me. the plug wires do not shock me much at all but a little. both coils are getting 12.3 volts from the green wires and the ground wires testing from the + terminal on the battery. he thinks i have 2 bad coils but im not so sure about it since i just replaced them a month or so before it quit working. what do you think?