'84 Merc V6 150 - cyl 1, 3 &5 has weak spark, 2, 4 & 6 strong. Any ideas?

Jersey13

Petty Officer 2nd Class
Joined
Mar 18, 2001
Messages
101
Took her out yesterday for the first time this year after i just rebuilt the carbs. Ran her at home, everything perfect. Got onto the lake, helped a guy at the dock (his battery was dead after he just got it back from the dealer being serviced and i happen to have an extra battery, go figure),started the ol' merc right up, idled around a little, got her good and warn, checked the tattle-tale - flowing good, then chugged out of the no wake zone then goosed her full throttle and she ran like a champ. I was heading into the wind and it was a little choppy so i backed off the throttle, swung her around and goosed her again. She took off fine and got up on the pad for about 10 seconds and then all of the sudden she backed down like she fouled a plug or two. I thought it was strange to foul a plug since i was running WOT for 2-3 minutes total but i had no power what so ever. So after being on the water for about 20 minutes, i idled back to the dock and put her on the trailer headed for home. Once home, i put the ears on and same thing...no power. Checked the plugs, carbs, blahblahblah..all ok. I started pulling the wires off the plugs one by one as she ran on the ears and realized the one side of the motor has really weak spark and doesn't make much difference when i pull the wires off. When i did it to the other side, cly 2,4 &6, it made a big difference. And the spark coming off the wires as i pulled them off the plugs where much stronger on 2,4 & 6. I know this motor has two switch boxes, one for cyl 1,3 & 5 and one for 2, 4 and 6, but i really want to be sure that this is the problem before i drop $200 or whatever they go for. My Solec (horibble) manual doesn't tell me how to test the switchbox but tells me how to test everything else....stator, trigger, control box. I'm guessing i should just swap the switch boxes and see if the problem follows it but it just seems sort of odd that one of then would just "sort" of die. It still throws spark, but not strong spark and i guess under power, it's not strong enough to ignite those 3 cylinders. I guess i figure if one of thise bixes is going to go, it's either going to work or not work at all, not "kind of" work. If anyone has ever experienced something like this or may have any other idea of what could be wrong, any help would be appreciated.<br /><br />Thanks in advance - Jersey
 

ODDD1

Lieutenant Junior Grade
Joined
Jan 23, 2001
Messages
1,054
Re: '84 Merc V6 150 - cyl 1, 3 &5 has weak spark, 2, 4 & 6 strong. Any ideas?

Jersey, I believe you have a failed stator.....an heres why...mercs switch boxes dont usually fail "a little" they will usually drop spark on one cyl every once in a while two cyl an I've seen a couple that failed all three cylinders BUT WHEN THEY GO AWAY IT DONT COME BACK! The weak spark is the trick here...a stator has a low speed winding and a high speed winding for each switch box......stators are known for failing a low speed winding. When this happens one switch box [an its bank of cylinders] will work normally, but the other one will only have energy from the high speed winding and wiil have about a third of the spark energy available hence weak spark on one bank...testing input voltage at the coils and a voltage/ohms test of stator will verify.....dont just put on a stator...get someone competent to test.....it could be a box or a advance module...good luck
 

Bobby Powell

Petty Officer 3rd Class
Joined
Apr 7, 2001
Messages
78
Re: '84 Merc V6 150 - cyl 1, 3 &5 has weak spark, 2, 4 & 6 strong. Any ideas?

To ODD1:<br />What is the voltage supposed to be coming from the stator to the powerpack? And then from the powerpack into coils? I cant find this info in my engine manual.<br /><br />1984 Merc. 90hp In-line 6<br /><br />Bobby Powell
 

ODDD1

Lieutenant Junior Grade
Joined
Jan 23, 2001
Messages
1,054
Re: '84 Merc V6 150 - cyl 1, 3 &5 has weak spark, 2, 4 & 6 strong. Any ideas?

Blue wires to switch boxes..200+ volts....red wires...anything over 20 volts...output to coils...180 minimum....these tests done at cranking speed using a peak reading DC voltmeter....regular dc meter will get cooked.
 

Bobby Powell

Petty Officer 3rd Class
Joined
Apr 7, 2001
Messages
78
Re: '84 Merc V6 150 - cyl 1, 3 &5 has weak spark, 2, 4 & 6 strong. Any ideas?

To ODDD1:<br />Thank you for the above Infomation.<br />It is greatly appreciated.<br /><br />Bobby
 

Jersey13

Petty Officer 2nd Class
Joined
Mar 18, 2001
Messages
101
Re: '84 Merc V6 150 - cyl 1, 3 &5 has weak spark, 2, 4 & 6 strong. Any ideas?

Thanks so much for the info ODDD1. I've been reading this board for a while now and have read many of your posts. You really dedicate time to this board and help a lot of people out and i'm sure it's very appreciated, especially by me. I haven't had a chance (BTW, Happy Easter) to test the stator but i will this week and post a reply on what i find. The voltage readings you gave to Bobby Powell for his '84 90hp merc, should they be the same on my '84 150 merc? Once again, thanks for all the input and help you've given me and i'm sure tons of other readers on this board.<br /><br />-Jersey
 

ODDD1

Lieutenant Junior Grade
Joined
Jan 23, 2001
Messages
1,054
Re: '84 Merc V6 150 - cyl 1, 3 &5 has weak spark, 2, 4 & 6 strong. Any ideas?

Yes jersey the readings for you an Bobby are the same. In fact the stators are basically same piece with different length wires on them......yes happy easter to you too.<br />As a long time boat wrench in the midwest I have learned alot and this time of year I have time to spend here.....probly see less of me in summer.....as far as why.. well everybody likes helping others...on a selfish note the more people i can help stay in boating the bigger customer base I can draw from....an i see alot a people bailing out because they get soooo disgusted with their hardware....half the time all that is needed is a little education.
 

Jersey13

Petty Officer 2nd Class
Joined
Mar 18, 2001
Messages
101
Re: '84 Merc V6 150 - cyl 1, 3 &5 has weak spark, 2, 4 & 6 strong. Any ideas?

I've worked on cars most of my life and i enjoy, when the wife and child aren't really pressing me
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, to work on the boat. You should post the name of your business and where you're located so some of these people could locate you if they were in your area. Judging by all the knowledge you shed on this board, i would feel safe bringing my boat to someone like you. Even though i haven't brought any of my "toys" to a mechanic...yet! haha. Thanks again. I'll kepp ya posted on how i make out.<br /><br />-Jersey
 

Jersey13

Petty Officer 2nd Class
Joined
Mar 18, 2001
Messages
101
Re: '84 Merc V6 150 - cyl 1, 3 &5 has weak spark, 2, 4 & 6 strong. Any ideas?

Update - Read through my manual and found readings the stator should give. There are 7 wires coming from the stator - blue/white, red/white, blue, red, black, and 2 yellows that go to the rectifier. Did all the tests it asked and all was within ranges given except when i ohmed out the red to ground, it was way below the reading what it should be. Then i disconnected all the wires (except the black ground to powerhead) and re-tested the red to ground and it read perfect. After fooling around with it a bit, i realized when i hooked the yellows up to the rectifier, the readings on my meter while testing red and ground dropped back out of range. Somehow, inside the stator, the yellows are shorted to the red lead. Guess it's time for a stator
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<br /><br />ODDD1 - i would have done the test you asked but it's tough doing that test at night by the time i get home and, my meter isn't a peak reading dc meter.<br /><br />Thanks again.<br /><br />-Jersey
 
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