Mercruiser 140 3.0 going through condensers

tu1aher1

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Jun 3, 2015
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Hi all,

I really hope someone can help me out. I bought a 84 Hammond with a Mercruiser 140. all cylinders are in the 180s compression. I had the coil, cap, rotor, points, condenser, fuel pump replaced and the carb rebuilt at a big time boat place. Every thing will go great for about 30 to 60 min and then the engine starts to slowly bog down and sputter and eventually come to a complete stop and die. I put a new condenser in it and the engine runs like new again. I have gone through around 5 condensers already. Then engine never over heats and I verified the temp gadge works properly. I replace the condensers pretty fast so the engine is still at temp and will run like new with the new cap for another 30-60 min

When the engine is on I have 12-14v at the + on the coil. I had read somewhere to add a ballast resistor and drop the volts down to 9 or less at the coil + or it will eventually degrade the condenser or over heat the coil. On other forums they say the 12-14 is correct. I did add the ballast resistor but it did not drop the volt to 9 or less but I know it was at least cutting down the amps because it did get warm. But it still ruins the condensers. When I do change out the condenser it is pretty hot along with the rest of the inside of the distributor but I figured this was because it was so close to the block. I could pick it up and juggle it around, if you know what I mean

Please help me out on this if someone knows about this problem. I can tell you how much I would appreciate it.

Thanks a lot
 

achris

More fish than mountain goat
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When you say 'When the engine is on', is that running or just with the key ON?
 

gm280

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WOW knowing exactly what a condenser actually does, this is an interesting problem. I can't help but think that the heat is the culprit, but I can't figure out why the heat is there in the first place. Condensers, actually capacitors, are used to help keep the points form arching as they open each time. So they absorb the voltage for a little time to keep sparks/arches off the point contacts to prolong the point's life. It is really unusual to actual find a bad condenser in a point systems. It just isn't a high failure item. And with that info, I think you need to figure out where all the high temps are coming from. I think that is your problem... Of course I could be wrong. But honestly that would be only the third time...this morning... :facepalm:
 

tu1aher1

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Achris, sorry I ment to say " while the engine is running I have 12v at the + on the coil. "
 

michael225q

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I had the exact problem turned out to be the alternator would put out too much voltage and burned the points and condenser. changed out the alternator and problem solved. Good luck
 

tu1aher1

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Ok thank you. What I will do is, find out how much Ohm resistor I need to bring the voltage down to 9 voltz at the coil. I dont have enough money for a new alternator right now. Any idea how much current draw at the + side of the coil with the engine running? Or Ohm needed? Thank you every body. Let me know what you think.
 

achris

More fish than mountain goat
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If your alternator is putting out more voltage than it's supposed to, then you need to fix that, not try and 'band-aid' around the problem. If the alternator is the problem, let's fix it. It certainly doesn't mean buying a new one. Just like most other stuff, they can be pulled apart and fixed.

But first, get a battery voltage reading from the engine. Run the engine for a few minutes at high idle (about 1200-1500 rpm) and with it running at that speed, put your voltmeter on the battery itself. What voltage does it show?

Chris......
 

tu1aher1

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Update, I calculated I needed a 15 ohm resistor to get 9 v so I went and got one. But when I put it in line to the + side of the coil the engine would not run. It would run with a 2 Ohm ballast resister. With or without the resistor it have 12v at the + side of coil. Apparently you need to have 12v at that location.

I agree that I need to have the problem fixed. To answer your question Chris when I run the engine at 1200 to I get 14v to the battery but after a while it seams to drop a little around 13 as the battery reaches full charge. The battety is fairly new. I bought it this season. Thanks
 

achris

More fish than mountain goat
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Ok. Nothing wrong with the alternator (voltage 'drop' could be due to heating or inaccurate voltmeter).

How did you calculate 15Ω? If you have a coil with a primary resistance of around 1Ω (spec is 0.9 to 1.5, depending on which coil) to drop 1/4 of the voltage at that resistance would require roughly 1/4 of it's resistance to be in series before it, so about 0.3Ω, not 15Ω. (but this does not include reluctance).

Spec on the resistance wire is 1.8 to 2Ω Measure the resistance from the harness plug (pin 5) to the power lead to the coil (should be purple or white, depending on the era of the engine). You need to measure it with the wire disconnected from the coil. You should have 2 wires on the coil +, depending on the era of the engine, should be (purple and a purple/yellow) or (white and a tan).

Chris.........
 

RCAnderson

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The ballet resistor was put in place to get 6 volts to the old 6 volt coils. If you have a 12 volt coil, you don't need one, but some wiring modification is needed. The way it works is that the resistor is bypassed while starting only, so you get 12 volts to the 6 volt coil while starting. Once the ignition switch is in the run position, then the ballast resistor comes into play, giving you 6 volts at the coil. I"m sure someone smarter than me can get you a wiring diagram if you don' t have one.
 

PeterB26

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Jun 16, 2013
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There is a wire on some Mercruiser ignition systems to the + 12 v side of the ignition coil that is meant to change resistance as it warms up.
It has no special idication that it is a special wire. If you were not aware of its pecurliar existance then just by inspection you would not know that it was anythng but a "normal" wire.
The idea is it delivers 100% voltage to the coil when the engine is cold, but after running a while the wire acts like a resistor and reduces the voltage to the coil. I have had my run-arounds with this particular Mrecruisre-ism.... it could be the source of your trouble.

PeterB26
 

achris

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The ballet resistor was put in place to get 6 volts to the old 6 volt coils. If you have a 12 volt coil, you don't need one, but some wiring modification is needed.

No, the balast resistor was put in place so a coil designed to run at 7 or 8 volts could be used. This was done because the battery voltage while cranking would drop down, and so a 12v coil wouldn't have enough power to produce a decent spark while cranking, making starting difficult.

The way it works is that the resistor is bypassed while starting only, so you get 12 volts to the 6 volt coil while starting. Once the ignition switch is in the run position, then the ballast resistor comes into play....

That's mostly correct, except it's not a 6v coil.

There is a wire on some Mercruiser ignition systems to the + 12 v side of the ignition coil that is meant to change resistance as it warms up.

First I've heard of that.

It has no special indication that it is a special wire.

That's true, likes like just another piece of wire.

If you were not aware of its pecurliar existance then just by inspection you would not know that it was anythng but a "normal" wire.
The idea is it delivers 100% voltage to the coil when the engine is cold, but after running a while the wire acts like a resistor and reduces the voltage to the coil.

Yeah, NO.... A resistance wire is resitive, at the nominated value regardless of temperature.
 

tu1aher1

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Update. Ok I have some info. First, to Mr Anderson, there is no ballast resistor in my system. I added it to see if I needed it. Thank you though . I now know it is not needed so it is out of the equation. To Chris. I completly disconnected my coil, +, -, and wire to distributor. Across the + and - I get 3.8, 3.9 ohms. Also, I have the purple/wellow and brownish wires on my + on the coil. My purple/yellow go down to the starter and my brownish goes to pin 5 like you say and it does give me 2 ohms from the Big connector to the other end that connects to the coil. Of course I disconnected from the coil. Does the 3.8 ohms on my coil mean its bad? Supposed to be a new coil? Thanks for the help.
 

achris

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. Does the 3.8 ohms on my coil mean its bad? Supposed to be a new coil? Thanks for the help.

The Merc service manual specifies 2 different coils, based on part number. One shows as 0.9 - 1.2Ω, the other 1.3 - 1.5Ω. So yes, your coil is out of spec.

If you'd like to buy a non-genuine, try this one -> http://www.iboats.com/mall/partfinde...n_id=029289596

Or if you want to go the genuine route, the Merc part number is -898253T24.

Chris......
 

tu1aher1

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Update. So I have determined thanks to Chris that my coil is defective. I looked in my mercruiser manual and at the + side of my coil I should have a purple/yellow wire and a purple resistor wire. I have the purple/yellow wire but the other wire is sort of Orange that looks like it could have turned light purpplish over the years and now more orange. I verified that is does have 2.1 ohms. So I go to remove my coil that was installed at the Big time boat place and low and behold stamped right on it says "12v Use without External Resistor 080" I should have one that uses the external resistance right? Since I have a wire pulling 2 ohms. There is a serial number on the bottom 101514. I appears that at first when I go out to the lake with a cool coil and new condenser the boat will run fine but after a while with the double resistance of 4 ohms(I'm assuming from 2 ohms in the wire and 2 internally) as the coil starts to heat up and the condenser heats up, it block too much electricity. Am I on the right track?

Im going to go and get the right coil and see what happens. Does this sound like I solved the problem?
 

tu1aher1

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Problem fixed!!! The coil that was installed at the boat repair place was the wrong one. It had internal resistance. Thats why it had 4 ohms. That plus the 2 ohms in the resistor wire's 2 ohms gave it too much ohms when the motor heated up. Now with the right coil with out the internal resistance I can boat all day with problems. Thanks a lot to everyone that helped me especially Chris!
 

achris

More fish than mountain goat
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Great news... Thanks for letting us know... Happy boating.

BTW, that coil's not defective, it's just the wrong one. Lots of perfectly good coils get tossed each week... :D
 
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tu1aher1

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Update. Well I thought my problem was fixed but the boat started doing the same thing again. At first for a couple of days I could go the whole outing (about an hour and a half on the lake) with out a problem. I thought my problem was fixed. Now After about 30 min the motor will almost come to a complete stop then sputter then stop. If I wait a few min when the engine cools down it will go again for a few more min. I removed the wires to the coil, all of them, and measured 2.0 ohms across the +, -. Then I remembered that Chris stated that it should be .9 to 1.2 or 1.3 to 1.5 depending on the coil. I read 2.0 to 2.1 cold or hot. Is this enough to affect the spark when the engine gets hot?

Thanks for any help.
 
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