Sudden loss of power?

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floridagirl

Recruit
Joined
Jul 24, 2012
Messages
2
OK, I'm sort of new at this but hopefully I can make this sensible. I'm pretty much an engine newbie, I can do simple stuff, change out the water pump, etc, but I'm out of my depth with this one. I have a 1984 Johnson 115 hp V4 engine. Has been running fine until now. New water pump, new plugs, wires about a year old. Took it out Sunday to go scalloping, ran fine at about 25 mph almost all the way out. About 2 minutes before we got to the scallop grounds, it suddenly throttled itself down to about 8 mph. Since we were already there, I anchored and scalloped for a few hours, hoping that whatever it was would sort itself out when the engine had cooled, at least well enough to get home. Coming home, it was very hard to start, kept turning over, but took several tries to catch. Got it started, but it refused to go any faster than 8 mph, even at full throttle. Didn't sound like it was revving any higher than it should have been at 8 mph, but wouldn't go any faster. (RPM guage is out, so can't be totally certain). Several times on the way home it tried to die, like it wasn't getting any fuel, but then just coughed and went on again without my doing anything. Tried pumping the primer bulb in case of a fuel pump issue, but didn't seem to make any difference. Also noticed that the instrument panel kept turning itself off, don't know if that is related or not, but trying to be thorough. Got most of the way home, a few hundred yards from the dock it died and refused to start. Checked the fuel, and it was so close to empty as made no difference. When I left I had more than enough fuel for two trips, so it really burned through some fuel getting back.
I'm stumped as to where to start looking, and I've had zero luck with marine mechanics. Always spent loads of cash, almost always with bad results, so I'm hoping that it is something I can handle.
I'm thinking that it is likely either coils or a power pack, just from what I've read here, but if anybody has any advice, I could sure use it.
 
kfa4303

kfa4303

Banned
Joined
Sep 17, 2010
Messages
6,094
Re: Sudden loss of power?

HI floridagirl. Welcome to iboats. I'm not an expert on the big large HP motors, but it sounds like you're having electrical issues which are causing you to loose spark on one or more cylinders (aka "dropping a cylinder"). Only in your case, I suspect you might actually be dropping 2 cylinders (1 & 3, or 2 & 4) and running on half power, which causes you to then use twice the fuel. The simplest thing to do would be to check for strong, consistent spark from all 4 cylinders. If 2 are out that implies that they have a common cause. Many electronic components won't fail until they get hot. As a result, you may have to take the boat out and get it to fail again on purpose, then test for spark. Just stay close to shore and have some tools on board so you can do some basic diagnostics while on the water. Wish I could help more, but some of the big motor gurus will be along shortly to help some more. Good luck. Keep us posted.

btw...what part of FL are you from?
 
M

mekkamaz

Petty Officer 2nd Class
Joined
Dec 30, 2008
Messages
180
Re: Sudden loss of power?

Looks like a power pack failure dropping 2 cylinders, as one pack feeds 2. If so, due to the electrical gizmo in your boat,you have to check for voltage at the kill wire of the power pack (black/yellow), which is one of the most common causes of damage them.

I?ll try first what kfa above suggest, then starts from there.
 
F

floridagirl

Recruit
Joined
Jul 24, 2012
Messages
2
Re: Sudden loss of power?

I can't even begin to tell both of you how much I appreciate the advice. Anything that helps to narrow down the possibilities is tremendous! It will probably be a few days before I have a chance to check it out, but I'll let you know what I find out. I'm hoping for a quick fix so that I can get in some serious scallopping before the end of the season.
Oh, and kfa: I'm in Ocala. Not as close to the water s I'd like, but not as bad as all that.
 
E

emdsapmgr

Supreme Mariner
Joined
Dec 9, 2005
Messages
11,551
Re: Sudden loss of power?

Some good comments about testing for spark. If you find no spark on one head or the other, you perform an easy test. That engine has two power packs-one for each head. You can swap them and see if a no-spark condition moves from one head to the other. If it does, likely a bad pack.
 
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