Merc 15 rectifier

[LubeDude]

Ok, did a search but didnt find what I wanted so hear goes. Had some time today to look at my engine, 87 Merc 150, Noticed the last time I went out that it didnt seem to be charging, not to mention not running right. Did all the tests on the rectifier and it appears that it is bad. Will a bad rectifier cause the engine to run bad due to low voltage?

 

[rickdb1boat]

Re: Merc 15 rectifier

Hi Lubedude,<br /><br />Low voltage will certainly affect performance, as the spark to the plugs will suffer. If the battery is fully charged, it should run OK until it starts getting weak from lack of charge. Not good on the rest of the electronics, either. Might as well replace it...

 

[LubeDude]

Re: Merc 15 rectifier

Im beginning to think this may be the whole cause of my problem! I am definatly going to replace it.<br /><br />The problem I had was that it ran fine the time I took it out and then when I started to come back in it took off fine and then it stumbled a little and the oil alarm went off. I imeadiatly shut it down and checked every thing and it started right up. The exhaust was smoking a little so I figured it had oil! After that it just ran rough and didnt have the power it should have. Brought it home and imeadiatly did a compression check and it was 120# across the board + or - a # or two. Does that sound like something that might happen due to low voltage? Curious about the beeper going off. Oil system all checks out and it is definatly using oil from the tank.

 

[rickdb1boat]

Re: Merc 15 rectifier

Funny things happen when you have low voltage on those Mercs. Don't know if it would affect the horn, but it would not suprise me... One way to find out is get that rectifier and try it out again and hope for the best. Sounds like everything else is doing it's job and you do have oil going to the motor, as you said. <br /><br />BTW, got that quart of Amsoil and just recieved a packet from Amsoil yesterday, that I haven't had time to go through yet. Can't wait to try it out!! Still got about a month here before I can unless, the weather changes a whole lot.

 

[LubeDude]

Re: Merc 15 rectifier

Once I get this engine running as it should, Im going to record some #s and change it over too. But not untill I get it running right in the first place. Im also going to install smart tabs on the boat. You do not hear of them on Bass Boats much, but they have my curiosity up and Im going to give them a try! You all will sherly hear about those results!

 

[LubeDude]

Re: Merc 15 rectifier

OK, now Im really confuse. Not too hard for me sometimes.<br /><br />I just went down to the dealer to buy a rectifier for the engine, He looked up the part and brought it to the counter where I ran the same test I ran on the old one on the new one. Guess what, the new one failed too. The manual I have says that if you use an ohm meter and put the + point on the base and the - on the top two posts that there should be an open circuit. And if you reverse the connections that it should be closed! Well mine tests bacwards from this and so did the new one. What gives with this? Is my manual wrong?

 

[DHPMARINE]

Re: Merc 15 rectifier

LubeDude, If you were using Mercury's tester,I would expect it to read as stated in the manual.Other ohm meters may have a different polarity.Important thing is the test reads only one way.You are testing the diodes,and if they don't read one way it is bad.I suspect your rectifier is OK.Also if the battery was low,you never could have done that compression test with out charging the battery first.DHP

 

[rickdb1boat]

Re: Merc 15 rectifier

DHP<br /><br />Are you kidding me that if the charging system is not woking, it can't be the recifier?

 

[DHPMARINE]

Re: Merc 15 rectifier

Not kidding at all.I think the test says the rectifier is okay.I want to know if the battery was indeed low on charge.I suspect either low or high stator readings to be affecting the engine operation.<br />DHP (yes a bad rectifier will cause the battery to be under charged)

 

[LubeDude]

Re: Merc 15 rectifier

DHPMarine:<br /><br />The first time the engine did this, it just ran rough, no stutter or jerking, Thats when I did the compession readings and the battery was just replaced and fully charges befor I went out, only ran for maybe 20 minutes. So with all the sparkplugs out it didnt take much to turn it over to do the comp check!<br /><br />The second time it happened after cleaning the carbs, changing fuel filter and plugs and checking electrical conections and changing the outer switchbox, (Borrowed a good one from a freind), it ran great for thirty seconds and then it did the sudder thing and the horn went off again, started fine, but know it has a definate stutter and misses. Does the duh duh duh duh thing! Havnt had the boat out since. Did put the original switchbox back on.

 

[DHPMARINE]

Re: Merc 15 rectifier

LubeDude,Guess we have to wait until you go out again and can give us more clues.I still doubt the rectifier or the battery.A 20 minute run won't deplete a good battery.Your motor only needs the battery to start.Then it can run on it's own.Even without a charge system,it takes a few hours to run down a battery,unless you run a trolling motor,or motorized down riggers alot.<br />Good Luck DHP (keep us posted!)

 

[dilligafda]

Re: Merc 15 rectifier

Originally posted by LubeDude:<br /> Will a bad rectifier cause the engine to run bad due to low voltage?

I tried to do this earlier but the computer crashed, GOD I hate these things sometimes! <br /><br />The answer to the question above is NO, not in this case. The battery charging part of the stator has nothing to do with the ignition, they are seperate windings on the same core. Also the ignition on that engine is not dependant on battery voltage to operate. If the battery is not charging (which it would appear it isn't) it will not effect the running of the engine unless you don't have enough battery voltage to turn the engine over. <br /><br />From what you are describing, I would be suspect of the wiring harness and ground connections. THat is the first place I would start after I looked into the charging system. Also as DHP said, I too am not suprized you got different readings from your meter. Merc must use a different meter than the rest of us cause I've checked good regulator/rectifiers and come up with similar readings as yours. Install the new reg/rec and check all the ground and wiring connections and let us know what you find. <br /><br />Good Luck!

 

[jimmy@wm]

Re: Merc 15 rectifier

Hello LD, Just out of curiosity why did you swap the outer switchbox and have you checked the trigger to see if there may be a broke wire in the harness for it. I am working on an '87 150 mariner now that would miss on 2 cyls at certain times depending on throttle pos. Found a broke wire in trigger, soldered it together insulated it, runs great. With the movement back and forth on these things wires will break. This may have nothing to do with your problem, just curious. <br />Good luck.<br /><br />Jimmy

 

[LubeDude]

Re: Merc 15 rectifier

I changed the switchbox on the advice of the local Merc mechanic, he thought that might be the problem, because he said thats the one the horn hooks to, and loned me a used one, but that didnt help! I need to put the boat in the water again and try it after checking all the connections again, but do not have the time. Im going back to Portland next week again so wont be able to do it next week either. Now Im thinking it may be a coil pack after it warms up a little, Like I said, it ran fine for 30 seconds the last time I took it out. I really do not know!