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I have a 1986 OMC Cobra 3.0. I am having an ignition problem…

I have a 1986 OMC...
I have a 1986 OMC Cobra 3.0. I am having an ignition problem I cant figure out. Start it up and let it idle. It runs from 35 to 50 minutes and dies. Everything is new, points, rotor, cap, coil, wires, condensor! Dwell is set according to book. If I pull #1 plug wire off, no spark. If I pull Coil wire I still have spark. Check voltage at Distributor side of coil while running and I have about 10.5 volt (analog meter). Voltage stays at that level the entire time it is running! What am I missing?
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Answered in 4 hours by:
9/24/2016
Marine Mechanic: K. Kergan, Marine Mechanic replied 5 years ago
K. Kergan
K. Kergan, Marine Mechanic
Category: Boat
Satisfied Customers: 1,031
Experience: 24 yrs exp. Inboard/Outboard mechanic Mercury/ Mercruiser, Volvo Penta and OMC, Johnson/Evin.
Verified

Hi, my name is Kerry.

Many coils are designed to run at 9volts.

This is because the system voltage drops to about nine volts while cranking.

There are two types of coils, one runs on 9 volts and the other on 12 volts(full system voltage}.

The 9 volt coil uses a ballast resistor to drop battery voltage down to nine volts while not cranking, when cranking, the resistor is by-passed by the starter solenoid sending the full battery voltage to the ignition system (9 volts while cranking).

If you have a 9 volt coil in a system with no ballast resistor or resistor wire, the coil could heat up and break down after about a half hour's running.

It usually says right on the coil, "use with ballast resistor" or "12 Volts".

I had one case where the distributor cap was at fault with almost the same symptoms, it would crap out and die after 20 minutes, the cap was like new but replacing it fixed the problem.

You can check whether or not you have a ballast resistor or resistor wire by putting a voltmeter on the coil positive terminal and turning on the key.

You may need to rotate the engine so the points are open, if the voltage is only nine volts, you have a resistor and need a nine volt coil.

If you have the full 12.7 volts, you need a 12 volt coil.

So what have you got?

Do you have a voltmeter?

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Customer reply replied 5 years ago
okay, also in this scenario, when I bought this boat I found what looks to be the "original coil" (color matches the blue gray of the rest of the unit). It states on the side "NO EXTERNAL RESISTOR REQUIRED". That coil is bad. The coil that was on it states "EXTERNAL RESISTOR REQUIRED". So, same as if I had good sense I assumed that it had the wrong coil on it, and purchased a new one and installed it with the same symptoms, just a few more minutes of run-time before shutting down. I have "10 Volts" on the +side of the coil. So do I need a "9 Volt Coil"?
Marine Mechanic: K. Kergan, Marine Mechanic replied 5 years ago

If you have only 10 volts, you need a coil marked "Resistor Required"

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Marine Mechanic: K. Kergan, Marine Mechanic replied 5 years ago

If there is 12 volts at the solenoid and only 10 at the coil, there is a resistor wire or ballast resistor in the system.

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Customer reply replied 5 years ago
Okay, the coil that was on when I started troubleshooting is labeled "USE WITH EXTERNAL RESISTOR". and I had the same problem. So is that coil bad even though it starts and runs for a while also? You think I need to replace it with a new one like it? Or is there a way to test a coil to see if it is bad? I verified again that I have 12 Volts at the Solenoid and only 10 Volts at the + side of the Coil. Clarify something for me please. Is a coil that needs an "External Resistor" what you refer too as a 9V Coil or is there both a 12V and 9V with that "External Resistor" requirement?
Marine Mechanic: K. Kergan, Marine Mechanic replied 5 years ago

The 9 volt coil is the one that says "Use with external resistor".

A coil that says "No external resistor required" is meant to use 12 volts. When you put it on a resistor, it will usually have weak spark and be hard to start.

What do the spark plugs look like?

Are they getting sooty? (black)

I was thinking the coil was getting hot which can happen if you run a 9 volt coil on the full 12 volts.

You have opposite situation. A 12 volt coil on a resistor.

I'm beginning to think you have some other problem, possibly fuel.

In any case the coil should be the same type that was on it for best performance.

You can test the resistance of a coil across the two terminals and from a terminal to where the coil wire plugs in.

I don't have a manual to get the values that it should be.

Sometimes a coil will have the right resistance and still be no good so it's not a sure fire way to know if it's good or not.

Is this a single engine boat?

A sure-fire way to test it would be to install it on another engine.

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Customer reply replied 5 years ago
the plugs are looking "sooty". But they have had nothing but an idle on them for 3 or more Hours trying to find the problem? Also the fuel could be getting weak,but that wouldn't cause me to loose spark? Yes it is a single engine boat. Sounds like I need to try a "New 9Volt Coil"? Can the "Resistor" be bad? I cannot find it in the harness anywhere? If my memory serves me well, on the old "Breaker Point" cars that resistor was mounted on the "Firewall" and got RED HOT? I can't imagine where it would be in the engine compartment of a Fiberglass Boat?
Marine Mechanic: K. Kergan, Marine Mechanic replied 5 years ago

Some of the older boats had a resistor that looks the same as the one in the older cars.

The newer type of resistor is the wire that connects to the + terminal of the coil, it doesn't get very hot.

Sooty plugs implies that the engine is getting too much gas or that the spark is weak.

I would go with a new 9 volt coil and go from there.

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Customer reply replied 5 years ago
I can agree with the weak spark, but I just rebuilt the Carburetor when I started working on it in the beginning. I will pick up a new Coil this afternoon. If that doesn't do it there isn't much left?
Marine Mechanic: K. Kergan, Marine Mechanic replied 5 years ago

In rare cases new ignition components can be faulty right from the get-go.

I have had several condensers that were bad right out of the box.

I would get the right coil on it first, if it still does the same thing at least the coil is ruled out.

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Customer reply replied 5 years ago
I think I might be on to something other that the coil. The engine had been tuned up prior to me getting it. I went to pull the rotor off, and it will not come off the shaft! I have pulled with Vise Grips, beat on it with brass punch and hammer! It will not budge!! I believe someone has forced the wrong Rotor on the shaft. As best I can tell there is an 1/8" gap between the end of the rotor and the contacts in the Cap(by measuring with a small ruler) but I cant tell about the height alignment. I am going to have to cut up the side of the rotor with die grinder to split it to get it off?
Marine Mechanic: K. Kergan, Marine Mechanic replied 5 years ago

Interesting, I think this one should be easy to remove the rotor.

I'll look at the parts diagrams.

I had a Mercruiser 4 cylinder once that ran under power for 15 or 20 minutes, then would start missing, then quit.

Let it sit for 15 minutes or so and it would start and go for another 15 or 20 minutes.

This kept repeating and even though the cap looked like new, that's what it turned out to be.

Is this your distributor?

http://www.boats.net/parts/search/OMC/SternDrive/1986/252APKWB/IGNITION/parts.html

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Customer reply replied 5 years ago
As best I can tell ,yes that is the right one
Marine Mechanic: K. Kergan, Marine Mechanic replied 5 years ago

The rotor should be able to be just pulled off by hand.

If it's stuck fast, it may be rusted on the shaft which would mean the tune-up didn't include a new rotor.

You said the tune-up was done before you got the boat?

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Customer reply replied 5 years ago
302AMKWB is my tag number. Yes before I got the boat. They couldn't get it to run on the water consistently.
Marine Mechanic: K. Kergan, Marine Mechanic replied 5 years ago

http://www.boats.net/parts/search/OMC/SternDrive/1986/302AMKWB/IGNITION/parts.html

yes, it's the same distributor

I wouldn't trust the word of someone selling the boat, it may or may not have the parts they said it does.

I think the rotor is rusted on, you may need to replace the cap and rotor.

Did you get a new 9 volt coil?

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Customer reply replied 5 years ago
No I am gonna go with a cap and rotor first. Even if that's not the problem it needs to be corrected. Another question, how much up and down movement should there be in the distributor shaft? Mine seems excessive?
Marine Mechanic: K. Kergan, Marine Mechanic replied 5 years ago

A punch and hammer didn't break it loose?

Did you try prying upward?

You may need to put a block of wood on both sides of the distributor and use two pries at the same time.

Whatever gives you a good pry without breaking something.

Distributor shafts do have up and down play, more than 1/8" is not uncommon.

The helical drive gears on the distributor and camshaft tend to pull the distributor shaft downward.

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Customer reply replied 5 years ago
Couldn't budge it
Marine Mechanic: K. Kergan, Marine Mechanic replied 5 years ago

Cap and rotor first is a good idea since you can't be sure they have been replaced.

Couldn't, eh?

Maybe you can split it with a chisel.

Be careful not to bend the shaft by hitting from the side.

Hit it downward near the side of the rotor.

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Marine Mechanic: K. Kergan, Marine Mechanic replied 5 years ago

A wood chisel might work best, ***** *****

If you have a die grinder, you can use that to weaken the rotor so it breaks easily but it makes a mess of plastic particles.

Whatever works.

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Marine Mechanic: K. Kergan, Marine Mechanic replied 5 years ago

Getting back to the coil, you need a 9 volt coil, "Use with external resistor".

With the 12 volt coil, you will likely lose performance at high RPM.

The old one may be just fine.

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Customer reply replied 5 years ago
Kerry, sorry to have not gotten back to you on my ignition problem! I got tied up on other projects while waiting on the Cap and Rotor. Put them on yesterday and installed the Coil that was on the motor when I started working on it (the External Resistor Required one). Started it up. It ran flawlessly! After an hour and 20 minutes with the motor flusher on, I shut it down. I believe that the Cap and Rotor was the problem. Will try to put it on the water this weekend for a actual test run.
Marine Mechanic: K. Kergan, Marine Mechanic replied 5 years ago

My turn to say sorry about the delay, I've been away for a couple weeks.

I thought it might be the cap, glad to hear it ran good.

K. Kergan
K. Kergan, Marine Mechanic
Category: Boat
Satisfied Customers: 1,031
Experience: 24 yrs exp. Inboard/Outboard mechanic Mercury/ Mercruiser, Volvo Penta and OMC, Johnson/Evin.
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