Odd Engine Problem... Mechanic Can't Replicate It

brettagostini · Jul 30, 2003

Hi. I'm running a '78 140 Hp. Sometimes when I'm running at speed the engine will just... stop. Like I cut the key off. It starts again no problem, and this problem may occur once, twice, five times, or never during the course of the day. A likely related problem, that is even stranger, is this-- while running at speed the engine will stop for about one second then restart... like flicking a light switch off and on again. But this has only happened once or twice. When I took it to the mechanic for the first problem (last season) he, of course, couldn't get the problem to replicate itself as he ran it. Any suggestions on what to check, clean, or replace? Thanks!

Joe Reeves · Jul 30, 2003

Re: Odd Engine Problem... Mechanic Can't Replicate It

Brett.... Remove the black/yellow wire from the back of the ignition switch. If the problem now ceases to exist, replace the ignition switch. If your control has a safety kill switch, check that also as it might be intermitent, although unlikely. NOTE... with that black/yellow wirte disconnected, it will not be possible to shut down the engine by turning the key off. If the problem still exists, I would suspect that a short exists in the black/yellow wire (engine kill circuit) somewhere in the wiring harness. If so, you'll need to locate it via a ohm meter.

brettagostini · Jul 31, 2003

Re: Odd Engine Problem... Mechanic Can't Replicate It

Thanks Joe... I'll give it a try. Now for a dumb question. Is there an alternate way to shut off the engine, or do I need to re-connect the black yellow wire and then shut off via the key. How would I reference this wire if I were to replace it... "ignition wire?"

The Marine Doctor · Jul 31, 2003

Re: Odd Engine Problem... Mechanic Can't Replicate It

Checking the Black/Yellow. Hook one lead of and omh meter to the Black/Yellow, hook the other end to a known good ground. Operate the T+T and move the steering wheel back and forth. If at any time you get and Omh reading...you will know that the Black/Yellow is shorting to ground. TMD

wilde1j · Jul 31, 2003

Re: Odd Engine Problem... Mechanic Can't Replicate It

You can shut down w/ the choke/primer or disconnect the fuel line.

Luna Sea · Jul 31, 2003

Re: Odd Engine Problem... Mechanic Can't Replicate It

Brett, You just got some good advice here. My mechanic suggested power pack, stator, timer base. Big $$$$$$ Please let me know how you make out as I'm curious and this would be helpful to others as well. Good Luck. PS Tried doing a "holeshot" the other day and.........yup, died right out!

brettagostini · Jul 31, 2003

Re: Odd Engine Problem... Mechanic Can't Replicate It

I checked out my wiring today. My black-yellow wire is actually one of three that are part of a wire plug that plugs in just below the ignition. I can't just disconnect the black-yellow, I have to cut it from the plug. So I didn't want to cut the black-yellow just yet. (I tried unplugging the entire thing, but the engine really ran terribly, spitting and sputtering, when I did that.) I've notice that on the starboard side of the motor three cables enter, two side-by-side and one about an inch higher. The higher one is cracked and I can see rusty metal under the cracks. It looks like a metal sheathing protecting whatever is in the core of the cable. Is this cable the other end of my ignition plug cable? If so, I'll probably just go out and buy a new one on faith that that is the problem. PS Luna Sea... what is a "hole shot?"

Joe Reeves · Jul 31, 2003

Re: Odd Engine Problem... Mechanic Can't Replicate It

Brett.... In your last post, you stated "My black-yellow wire is actually one of three that are part of a wire plug that plugs in just below the ignition. I can't just disconnect the black-yellow, I have to cut it from the plug." I assume you're speaking of the wiring harness at the powerhead..... not at the ignition switch?

brettagostini · Aug 1, 2003

Re: Odd Engine Problem... Mechanic Can't Replicate It

Sorry for my cluelessness Joe... I don't even know what a "powerhead" is. The wire plug I'm referring to goes directly into the throttle unit at the driver seat -- beneath the place the ignition key goes in. The female connection is on the throttle unit, and it is a three wire plug that connects to it. There is a black-yellow, and (going from memory here) a green-yellow (or maybe green-white) and a third I don't remember at the moment.

Joe Reeves · Aug 1, 2003

Re: Odd Engine Problem... Mechanic Can't Replicate It

Brett.... The powerhead is the upper portion of the engine (block, crankshaft, pistons, etc etc). The plug you're referring to that is located under the ignition switch is a plug that a OMC tachometer would plug into. I was speaking about the back portion of the ignition switch which would, in your case, get somewhat involved. The alternative way to eliminate that black/yellow kill wire would be to carefully remove it from each of the two powerpack plugs at the powerhead (engine). Keep in mind that you can not shut the engine down with the ignition switch when those wires are disconnected. If you intend to keep that engine for awhile, I strongly recommend that you obtain a service manual for it.

brettagostini · Aug 1, 2003

Re: Odd Engine Problem... Mechanic Can't Replicate It

Yes... the service manual is on "The List." At the moment my boat budget is maxed out, so I'm trying to get through the end of this season without further investment if I can. I have the basic owner's manual, but that really isn't much help. Would the service manual be of much use to a mechanical idiot such as myself?

Luna Sea · Aug 1, 2003

Re: Odd Engine Problem... Mechanic Can't Replicate It

Brett, A "holeshot" is simply throwing the throttle lever down, kind of like flooring a car. No need for me to be doing that, but apparently waterskiers, tubers, showoffs, ect. have the need/desire. Interesting post ya got going. "If" my motor dies again I'll be paying special attention to whether the boat was bouncing or I was cutting the steering port or starb. The Clymer and/or Seloc manuals give you the basics. But the OEM one gives all, and I was surprised they also give you some of the basics. Good Luck!

brettagostini · Aug 1, 2003

Re: Odd Engine Problem... Mechanic Can't Replicate It

Thanks Luna Sea. An interesting thing I notice is that this seems to happen more frequently at top speeds.... possibly more vibrations = greater chance of shorting wires "brushing" occaisionally. It also SEEMS to only happen on the straight away... never in a turn. I'm going a way for a week or so, so once I get 'er back in the water and test out the black-yellow disconnect back at the powerhead I'll bump this post back up and let you know what, if anything I learned. Regarding manuals -- When I was in the Army we had TM's that would give you step-by-step instructions for troubleshooting and fixing virtually anything. There were diagrams, troubleshooting flowcharts, by the numbers directions for removing parts, etc. Are any of the manuals you mentioned like this?

Luna Sea · Aug 1, 2003

Re: Odd Engine Problem... Mechanic Can't Replicate It

Brett, Not exactly like that. I combine the basic repair (approx $30)with the OEM (approx $60) and that gives just about everything. Yeah, bump it if it gives you more problems. My boat only did it at WOT after I bought it, then it got worse, but I've changed the whole fuel and ign. systems since. If I baby it up to speed it doesn't seem to happen anymore.

pbailey · Aug 1, 2003

Re: Odd Engine Problem... Mechanic Can't Replicate It

Brett, Had a similar problem on an 88 special. We looked and looked for the problem. Finally broke down and took it to a mechanic. While I was inside giving all the information to the shop owner, the mechanic came in and said "I think I found the problem". He had unpluged the wiring harness at the engine and found it to be corroded. He said that with all intermitent electrical problems on older outboard's that's the first place he looks. That plug should be located on the port side under the cowling just below the starter. It's the main plug that has about 4-6 pins in it. It should be red in color and have a clip holding it together. It could be that it doesn't do it in the turns because tension is being apllied to the cable thereby making contact. pbailey

xp150 · Aug 1, 2003

Re: Odd Engine Problem... Mechanic Can't Replicate It

I had some what of the same problem with my motor and I took it had it put on a DYNO. It was the power pack. I order one from the link below it was about $140 delivered.I put it on in about 30 min. No more trouble.Just be sure to unplug and plug one wire at a time when replacing. http://www.seilermarine.com/outboard/omc_parts.htm

DJ · Aug 1, 2003

Re: Odd Engine Problem... Mechanic Can't Replicate It

Brett, If your budget is maxxed out, throwing parts at it is not an option. Unplugging and cleaning every connection you can get your hands on costs $$$nothing. I think you'll find something.

SeaMasterZ@aol.com · Aug 1, 2003

Re: Odd Engine Problem... Mechanic Can't Replicate It

Here is a low budget recipe for finding a flaw of the sort they are talking about go to a dollar store, get a small brass wire brush, sometimes they come in a pack of three, and a can of wd 40 almost anywhere for 2 bucks ONE AT A TIME undo every wire you see, clean it up and give it a shot of WD ... then replace the wire on the cleaned up, lubed down stud (behave sharkcat!) Virtually free and you can have a beer and make a fun project of it, I usually put a tiny dab of never sieze on there too, but its not neccessary, WD is good stuff eBay is a good source of cheap manuals, bid on one and youll likely get it for 20 bucks, I went to Amazon cause I already have an account there, and wanted it right away Good luck!

Taasman · Aug 1, 2003

Re: Odd Engine Problem... Mechanic Can't Replicate It

I had the exact same problem and symtoms you explain....one word POWER PACK! Mine $350.00

sharkcat · Aug 1, 2003

Re: Odd Engine Problem... Mechanic Can't Replicate It

Brett as you have read there are lots of things you can try b4 you spend out loads of cash.I had a similar problem with an old merc a few years ago it turned out to be a broken/corroded wire in the plug that went into the motor.The replacement loom was cubic$$$ I just cut into the loom & bypassed the problem area total cost about 2 cents worth of solder, 6 inches of wire & lots of time to actually find the fault.Didnt look all that pretty but it worked.Castaway at your age you probably have to lube down

Im still lubing up

Good luck Brett

Odd Engine Problem... Mechanic Can't Replicate It

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