boat problems- need help

matt1808 · Wakeboarder.Commie Joined: 05 Feb 2004 Posts: 1981

The past 2 years we have had this problem.- While we are driving the engine will shut off with no warning. It has been completly sporatic so we figure it is wiring problems. We have checked a lot of wires, had it in at several shops, got suggestions from people and nothing. One of the dealerships that worked on it kept screwing up the wiring more and more and finally we got a new wiring harness put in.

Any body have any suggestions to check or know what it is?
Sorry I didn't give much info but it has been really sporatic. If you have any questions I could answer them though.

JDK · Newbie Joined: 06 Oct 2004 Posts: 31 City: Saskatoon

Kill switch lanyard (the coiled cord near the throttle). Is it loose?

PortlandBrder · Soul Rider Joined: 18 Apr 2004 Posts: 352 City: Portland

I agree with JDK, I had that happen on my boat, dealer never thought of looking at the kill switch.

matt1808 · Wakeboarder.Commie Joined: 05 Feb 2004 Posts: 1981

no not it checked that the first time it happened and it starts right away.

matt1808 · Wakeboarder.Commie Joined: 05 Feb 2004 Posts: 1981

marlinempress · Outlaw Joined: 02 Feb 2005 Posts: 112 City: Murray

We'll need to know exactly what boat, engine, ignition system etc. you have to be able to give ideas...

matt1808 · Wakeboarder.Commie Joined: 05 Feb 2004 Posts: 1981

boat- Tahoe Q7
engine- Mercruiser 5.0 MPI Alpha
ignition system- not sure. Where could I find this?

marlinempress, anything else you need to know?

chaz28o · Posted: Jun 07, 2005 7:57 pm Post subject:

Gotta go with JDK

The kill switch could still be your problem - they're a 20 cent item made in china

a few bump in rough water, and it will pop out ever so slightly and the boat dies. All you have to do is look at it crosseyed, and it's fixed

I would complete bypass the switch (very simple) it servers no purpose, unless you're in a hydro-hull

matt1808 · Wakeboarder.Commie Joined: 05 Feb 2004 Posts: 1981

I'll check back behind the kill switch tomorrow, but I know for sure the lanyard isn't loose.

chaz28o, we bypassed it on our last boat and got a fine. oh well might go ahead and do it again.

matt1808 · Wakeboarder.Commie Joined: 05 Feb 2004 Posts: 1981

ok just checked the kill switch. There is no way it is the lanyard side and the back side didn't feel loose. Might still bypass it and see how it does this weekend though.

MrBlean · Posted: Jun 09, 2005 11:55 am Post subject:

Sounds electrical but could it be the fuel pump? I believe you'll find that's powered by 12v too. Could be a loose wire, faulty pump, all sorts of possibilities.

Does it just cut out briefly or does it die for a while? If the latter, get yourself one of those neon spark indicators that fit between the HT cap and the spark plug so you can check there is a spark. Next time it cuts out, insert the indicator crank the engine and see if it is sparking. If not, then it has to be fuel.

Liquid Lifestyle · Posted: Jun 09, 2005 12:16 pm Post subject:

You might want to check your temp also. Some boats once they start to overheat have a kill switch, usually with a loud beeping also.

If this goes bad it could be killing the motor when you aren't overheating, or you could really be overheating.

Just a thought.

matt1808 · Wakeboarder.Commie Joined: 05 Feb 2004 Posts: 1981

MrBlean, it just dies with no warning but then you can start it up imediatly after no delay. Well the first time it did it took about 2-3 mins. before it would start up. At the beginning we thought it could be a fuel problem and we found a loose connection in the fuel line but that didn't help. We didn't check too many of the wires to the fuel pump though, and I am not sure what all the mechanics have checked. They have pretty much just made the problem worse though.

Liquid Lifestyle, we have been watching all the guages pretty well and it hasn't been overheating. If the guage is reading the temp and it is in the right range then the sensor should be reading right shouldn't it? And how would I be able to check if it is killing the motor when it isn't overheating. Oh and there has been no beeping.

Shawn Madison · Posted: Jun 09, 2005 2:12 pm Post subject:

Try and backprobe your wiring harnesses with a t-pin and check for voltage fluctuations on all the things that are connected to engine. You will be able to isolate it better from there.

matt1808 · Wakeboarder.Commie Joined: 05 Feb 2004 Posts: 1981

Shawn Madison, how do I do that? And what am I looking for when I do that? Also would they test it like that when the wiring harness is installed, cause we had a new one put in at the end of last season.

MrBlean · Posted: Jun 10, 2005 12:39 am Post subject:

I'm not familiar with the Mercruiser but the higher end marine conversions using either single point or multipoint engines (and their more sophisticated electronics) often have more than one temperature sensor. There'e one for the gauge, one for the ECU to help set the fuel/air mixture and one for the overheat alarm.

If you have this type of set-up, just 'cos your gauge is reading correctly does mean you do not have a faulty sensor causing the problem.

I experienced a similar effect on an SPFI Ski Nautique only a week or so ago. Engine alarm light came on so we checked oil pressure, temperature, voltage etc - no apparent problems. Checked back thro' the "safety" sensors and the oil pressure switch was leaking slightly and clearly faulty. In that instance there's was an oil pressure switch and a temperature sensor wired in series to the alarm circuit. They are normally open circuit. When the engine overheats above a pre-set level or the oil pressure drops below a pre-set level the sensors "close" and a circuit is made to earth and instant alarm.

The gauge uses a sender giving a variable reading. The switch is simply on/off. Your symptoms are consistent with a faulty switch or connection somewhere as a sender would take time to recover and the engine would not re-start immediately.

At this stage could still be spark or fuel supply. You really need to find out which so you can focus your search. When a fault disappears immediately and/or is intermittent it is so hard to trace. But I guarantee that when you do find it, it will be something simple and you will kick yourself for not thinking of it sooner. Been there, got several T-shirts to prove it Embarassed

matt1808 · Wakeboarder.Commie Joined: 05 Feb 2004 Posts: 1981

MrBlean, so if it will start up immediately it probably isn't a faulty sensor? Also I wouldn't think it would be spark since it starts up right away, but I very well could be wrong. Do you really think it could be a spark problem?

Thanks for all the help so far. Hopefully I can get this sorted out soon. Nothing sucks more than the boat dying when you are boarding behind it.

MrBlean · Posted: Jun 12, 2005 9:44 pm Post subject:

I'm not suggesting it has to be a problem on the HT side of the ignition system (plugs, leads etc) but could be a poor connection or fault on the low tension side. The effect will be the same - no spark.

Years ago I had an intermittent problem with an outboard and it transpired there was a crack in the plastic housing in which the coil was mounted. Was on the underside and hence not visible but it allowed the spark to earth within the body of the coil. Was an intermittent fault for quite a while before it failed completely.

Managed to find it by cranking the engine over in darkness and could see the light emitted by the spark jumping in the crack.

As far as a faulty sensor goes, you have to understand the difference between a switch and a sensor and what is happening to the condition they are measuring. An oil pressure switch is designed to turn on a dashboard light when oil pressure is below, say 5psi. If the switch is faulty, (a loose terminal, say) it will appear closed and hence turn on the light unnecessarily. The intermittent contact may reset itself within seconds and the engine will restart.

A sensor provides a signal depending on the level of whatever it is measuring (fuel, oil pressure, temperature). Often they are variable resistors and the engine electronics measures how much current flows thro' the sensor. At a given threshold level of current (or voltage) the engine electronics will shut off the engine. If such a sensor fails completely, the associated gauge will either read max or min.

Temp senders have a habit of failing in such a way that the signal they produce is no longer calibrated correctly so the engine may shut off when the temp is normal. In the case of engine temperature, this doesn't change that quickly. If the sensor triggers falsely (when the temp is too low), when the engine stops the temperature of the water in the block and heads will rise so the sensor remains in it's fault condition. The engine will not restart until it has cooled below the temp at which the sensor falsely triggered the safety system. This may take several minutes.

In contrast, as soon as the engine stops the oil pressure drops to zero so if it was a faulty oil pressure sensor, the engine would restart immediately.

All of this only applies if you have such sensors fitted and the engine electronics is set up to use them.

matt1808 · Wakeboarder.Commie Joined: 05 Feb 2004 Posts: 1981

MrBlean, thanks for all the info. I am going to try calling the mercury service line and get some specific info on the sensors in my engine.

matt1808 · Wakeboarder.Commie Joined: 05 Feb 2004 Posts: 1981

ok I finally got it fixed and I feel pretty stupid now. couple weeks ago I found out the horn wasn't working but I went on vacation so I couldn't fix it until today. So I am fixing the horn and I was like wait a min. this is hooked up to the ground. I hooked it up right took it out and it ran perfect. After thinking about it I feel stupid for not thinking about it being a ground problem. I was talking to my uncle (a mechanic) afterwards and it got brought up and I just finished explaining what was wrong before and he said, "Have you got it fixed yet sounds like a problem with the ground."