1984 Merc 90 missing on 2 4 6

[superman111]

Ok so i have a problem with my new boat. When I got it the previous owner siad it needed the Carbs cleaned. He said last time he ran it it did good for about 30 min, after that it started skipping, he just made it into shore. (By the way a rat had gotten into the wiring and chewed a bunch into, he had supposedly wired what was required to make it run). Anyway, I got it and started with replacing the fuel filter almost immediatly it was obvious the the fuel pump was the only problem. It was just making enough fuel for it to run at idel and at full throttle without load. I put a electric fuel pump on it, and went to the lake.
At first it ran great and didnt miss a beat, at least not that I noticed. After stopping and going a few times(without ever killing the motor). It went dead, We played with what i would consider a fuel pressure regulator,and got it to run just enough to make it back, it was not easy as it would not idel slow enough for me to come back to neutral , then go in gear. When i got to the bank I decided to check the spark and thats where Im at now, I have no spark on 2 4 6, I assume I did before as it ran super strong, Can anyone give me a reason for this or jsut a place to start, I am new to thie and this it my first real boat. Also i would like to know if there is a way to choke the motor without having to put my hands over the carb to get it started. I am used to working on diesels and have no idea about outboards.

 

[backyard mechanic]

Re: 1984 Merc 90 missing on 2 4 6

No spark on even cylinders is a clear sign of an electrical wire/ignition failure.

You said the rats chewed up wiring. Sounds like a start to me... If there were wire connectors installed there is a good place to look.

All wires should be soldered back together then covered with die electric silicone and shrink tube over the repair or you can expect additional failure. Corrosion is a good insulator and it's tough to notice that in places you can't see, (like butt connectors).

 

[j_martin]

Re: 1984 Merc 90 missing on 2 4 6

The common denominator on those 3 cylinders is one switchbox, and one coil in the stator, with 2 taps on it going to that switchbox.

If I were you, I'd get the factory manual, and go through it very carefully as if you were restoring an engine found in the back of the barn under a haystack, because that's about what you have. If you mess around and fry electrical parts, it gets expensive. If you lean out and burn down a cylinder, it gets real expensive.

hope it helps
John

 

[superman111]

Re: 1984 Merc 90 missing on 2 4 6

Ok so one switch box runs the evens and the other runs the odds? I had a mechanic tell me that the top one ran 123 and the bottom ran 456 (not sure about his legitamcy), so i just need to get a manual and go through it and see if there are any wires going to the wrong place on the switch boxes? and one thing i forgot to mention is that i did smell what seemed to be a wire burning but seen no evidence of it nor any hot wires? If the rat was is the problem, is there any wires in the boat that could cause this, because i seen no evidence of him in the motor compartment? Thanks for the advice, I really need it!

 

[Barnacle_Bill]

Re: 1984 Merc 90 missing on 2 4 6

If it turns out to be a switchbox, which is sound like your problem, replace both of them so you are sure to have the same revision on both. Plus the bad one can make the good one look like it is the culprit. Why did you install an electric fuel pump? Not a good idea. Have you got it hooked up so that it will shut off if the motor stops running? If not you are inviting a major disaster like in loss of life.

 

[superman111]

Re: 1984 Merc 90 missing on 2 4 6

Yes it is wired up so the key turns it off, is there any other reason not to use an electric pump? it is rated at 2-3.5 psi i figured with a carb engine that is all i would really need. Any suggestions on where to some cheap switch boxes? as I am in college and money isn't coming my way as much as i would like for it to.
Thanks

 

[superman111]

Re: 1984 Merc 90 missing on 2 4 6

Also is this a common occuanace, I mean a switchbox just to go out all of a sudden? This is really bothering me as I can usually figure these things out on my own, but when it comes to boats i am lost, I am guessing that the switch box works like a ecu on a car for the timer, just for half the motor

 

[trihull59]

Re: 1984 Merc 90 missing on 2 4 6

cheap switch box for old engines does not exist lol. You can pay around 200 a switchbox for a used one. I have a 1975 85 hp and a new switch box is 456 dollars. Check CDI electronics and match up the numbers they seem to be the cheapest place to get one. For a cdi one it is around 200 new for mine at least. Electrical parts are never cheap even ebay seems to be expensive.

 

[superman111]

Re: 1984 Merc 90 missing on 2 4 6

Also is this a common occuanace, I mean a switchbox just to go out all of a sudden? This is really bothering me as I can usually figure these things out on my own, but when it comes to boats i am lost, I am guessing that the switch box works like a ecu on a car for the timer, just for half the motor

 

[superman111]

Re: 1984 Merc 90 missing on 2 4 6

Also one other thing how can i tell what year model the motor is?
Thanks

 

[superman111]

Re: 1984 Merc 90 missing on 2 4 6

Is there a major difference in the Sierra and the CDI switch boxes other than the 60 dollar price difference?

 

[trihull59]

Re: 1984 Merc 90 missing on 2 4 6

Everyone swears by CDI can't tell you much about the other brand, and as for what the switchbox does it powers the motor to do nearly everything to run. It powers the coil/distributor

 

[superman111]

Re: 1984 Merc 90 missing on 2 4 6

Ok thanks, but now i have no spark on any cylinder. is this a good sign that my stator has gone out?