Engine Dies ---- electrical failure????

[rndcomp]

87 Merc 170 - FWC - Electronic Ignition - Aftermarket charging system

After running the engine for about 45 minutes at 75% power, it dies on me... No warning, just dies. The temp is great (around 170) and the the oil pressure looks good as well.

If I let the boat sit for about 5-10 minutes, it will start up again, but only run for about 5 minutes. When it does run for those 5 minutes, she does great. Again, normal temp and oil. The engine is also very hard to start, almost as if the battery was dead. (FYI-it is a 2 month old battery)

I don't know much about engines, but what I have learned from this site (kudos to Don for teaching an old dog new tricks) is that an engine needs two things to run, fuel and spark.

When the engine died the first time, I removed the flame arrester and saw fuel flowing into the card when throttle was advanced. So this led me to believe it was a spark issue. Unfortunately, I didn't have the right tools to remove the plugs and look for spark. I did however check the battery terminals because the negative lead looked loose. When I went to tighten the lead it was VERY hot to the touch (to the point that it burned my fingers...) . What was strange was that the negative lead was connected to the battery via the wingnut terminal (accessory terminal), and not the standard post. While I do know that the two points are electrically identitical, my question is if the negative lead needs to be connected to the larger post due to current draw.

My final question is whether or not the battery lead connected to the smaller wingnut post (aka the accessory connector) could have caused the engine to die?

Any help would be greatly appreciated!!!!

 

[rndcomp]

Re: Engine Dies ---- electrical failure????

Bump

 

[Don S]

Re: Engine Dies ---- electrical failure????

What was strange was that the negative lead was connected to the battery via the wingnut terminal (accessory terminal), and not the standard post. While I do know that the two points are electrically identitical, my question is if the negative lead needs to be connected to the larger post due to current draw.

There are 2 posts on a battery, a positive and a negative. Has nothing to do with accessories or mains. and they are NOT electrically identical.

My suggestion, if you don't know that much about batteries and how to even hook up positive and negative cables, then you probably shouldn't be working on it at all till you do some reading on 12V systems and understand them a little bit more and how they operate.

 

[thrasher]

Re: Engine Dies ---- electrical failure????

Just to correct Don , an engine needs 3 things to run, fuel, spark and compression!!

Don, I think what he is trying to say is that on his battery he has the post and also on each post a seperate wing nut to run accessories. So he is correct stating that the negative post or the wingnut that is part of the negative post are the same thing electrically. My marine battery is the same in that it has 2 posts (a positive and a negative) and each post also has a wingnut attachment for accessories.. Hopefully that makes sense!!

Gary

 

[Don S]

Re: Engine Dies ---- electrical failure????

Just to correct Don , an engine needs 3 things to run, fuel, spark and compression!!

Gary

Hey, I never said 2 things, the original poster only remembered 2

 

[rndcomp]

Re: Engine Dies ---- electrical failure????

Just to correct Don , an engine needs 3 things to run, fuel, spark and compression!!

Don, I think what he is trying to say is that on his battery he has the post and also on each post a seperate wing nut to run accessories. So he is correct stating that the negative post or the wingnut that is part of the negative post are the same thing electrically. My marine battery is the same in that it has 2 posts (a positive and a negative) and each post also has a wingnut attachment for accessories.. Hopefully that makes sense!!

Gary

Gary, you are correct. That is exactly what I was saying.

Now that we are all on the same page.... can anyone help me to understand the problem at hand? Could an overheated battery cause an engine to die, or, is the problem most likely elsewhere.

 

[Don S]

Re: Engine Dies ---- electrical failure????

Now I understand the battery terminals you were describing. The wing nut terminals aren't just for accessories, they can be for anything with an eye type cable. And the main battery cables are often hooked to the wingnut terminal. Of course, ANY termainal on a battery should be Clean and Tight. Personally, wing nuts shouldn't even be allowed on batteries. They end up causing a lot of problems.
Get some 3/8 or 5/16 nuts and replace the wing nuts, and use a wrench to tighten them down.
Now rather your accessory wire could stop the engine........ It shouldn't, let's put it that way. But I have seen some very creative wiring done on boats by owners that THOUGHT they knew how to wire something.
Clean and tighten ALL your battery connections and replace the wingnuts and see if your problem goes away.

 

[rndcomp]

Re: Engine Dies ---- electrical failure????

thanks for the suggestion. Is it possible to rule out vapor lock due to the fact that there was fuel present in the carb when the throttle was advanced? I would like to know for sure that it is elecrical and not fuel related.

Thanks!

 

[Don S]

Re: Engine Dies ---- electrical failure????

There is no way you are going to "Know For Sure" without doing some testing. It's obvious you have a connection problem, cure the obvious problems and test for the results.
There are way more than one thing that can cause problems like you have, and throwing a lot of parts at it and fixing a bunch of differnt things that may not be bad isn't the way you fix a problem inexpensivly.
Could you imagine spending 400 bucks for a distributor, rebuilding the carb, replacing the fuel pump, then the coil. all because of a loose battery cable?????

 

[CharlieB]

Re: Engine Dies ---- electrical failure????

Does your boat have a volt meter in the dash?

If not thinnk about installling one to monitor your batteery and charging system.

You can test with a meter, battery voltage key off vs. running

Poor connectionns at the battery and a lot of alternators fail to charge, they cannot 'sense' battery voltage well enough to turn on/off correctly, sometimmes they will charge full tilt til they (the alternator) die, then you run off the battery til voltage gets so low the electronic ignition simply shuts off due to less than minimum voltage required.

Wait long enought for the battery to recover and you may restart and run a short time til you again drop below the minimum, and it dies.

All this time the starter will crank, allbeit, slowly, cause the battery is very low, and no charging system.

Don's right, the poor connections started it all, but after fixing them I'd bet your alternator/charging system needs some love and attention also!

 

[oldforge1]

Re: Engine Dies ---- electrical failure????

I am actually having the same problems as rndcomp. but I have an '87 165 i/o, and it seems to run fine with a fresh battery, but if i run it longer then ten minutes or so and shut it off at a dock, leave it for ten minutes or more, the battery has no juice. hook up the ejump pack to it to get home and its fine. Yes the battery is fine, have checked them many times to rule it out. but as for the hot terminal, my negative pole gets hot as well. since mine has no alternator, I don't know what else would send polarity back at it to make it so hot. Boat runs great when it runs, but when it leaves me 8-9 miles from home its really a pain in my side that I can't figure out which is driving me nuts. Any ideas out there?

 

[thunderroad]

Re: Engine Dies ---- electrical failure????

since mine has no alternator

.??? no alternator on a 165?

 

[poolmedic]

Re: Engine Dies ---- electrical failure????

Oldforge -- No alt. ????

My Dad's 72 invader with a 165 Merc. has an alternator on it! I suspect you have one but it sounds like it is not charging the battery. I can't remember if they had an integral voltage regulator or an external one. Voltage at the battery should be 13-14.5 volts with the engine running. The 165 had one belt that drove the water pump and Alt.

Randy

 

[rndcomp]

Re: Engine Dies ---- electrical failure????

All,

My system does have the voltmeter in the dash, and it is reading normal. The alternator is brand new, so I would assume that it is good. You can watch the voltmeter when the key is turned to "on" and it is just at the green line, however, when the engine does start (and the alternator is working) the voltmeter jumps up to normal.

I will start to trace out the electrical system and see what I can find out. I was reading the manual last night, but I am not sure as to what I need to check.

Thanks!

 

[Don S]

Re: Engine Dies ---- electrical failure????

Not much to trace out and check at this point, you have loose terminals, Clean and tighten them and test run it and see if your problem is cured.

 

[rndcomp]

Re: Engine Dies ---- electrical failure????

Not much to trace out and check at this point, you have loose terminals, Clean and tighten them and test run it and see if your problem is cured.

Don, I apologize if I have mislead you in regards to the problem. I do not believe that I have loose terminals. The statement was weather or not the negative lead being attached to the accessory terminal (and thus getting hot) could cause the engine to die. If not, then I am not sure what I need to check in regards to terminals.

This is why I asked the question earlier about the fuel. I want to make sure that I am actually looking in the right area.

Thanks!

 

[CharlieB]

Re: Engine Dies ---- electrical failure????

When was the last time you checked the water/acid level in your battery?

 

[rndcomp]

Re: Engine Dies ---- electrical failure????

I have never checked the level in the battery. The battery is only 2 months old. What else should be checked? Does the fact that there is fuel going into the carb (once the engine dies) prove that it is electrical failure, or, can this issue still be related to fuel? Should I be checking the water/fuel seperator? What about the various filter screens.

Please help.

 

[Mjust]

Re: Engine Dies ---- electrical failure????

Go to your local auto parts store and spend $5 and buy new battery cable ends that will clamp to the post and not use the wing nut. The wing nuts on the battery suck and come loose which will cause that cable to heat up. Also, Have the positive battery cable loose (could use a friend for this test to hold the cable on the post for you) Start the motor and remove the positive cable while running, did the motor die???. It should stay running, if it dies your setup is using the battery to keep it running which is a sign. Also, put a volt meter on the neg. side of the coil and the other lead of the meter to a good ground. Watch the DC voltage till the motor dies after 5 min and report back with the readings.

 

[Don S]

Re: Engine Dies ---- electrical failure????

DO NOT disconnect the battery cable with the engine running. It will die, and you will blow the diodes in the alternator.