Logo
FULL SITE MENU

Omc voltage problem at coil. Help

J

jeff torres

New member
For any of you OMC pro's, I have any electricial problem that is kicking my butt. The voltage is low at my coil when running.(.9-3.5 volts) Charging voltage to battery seems high at 16 volts. Coil has been changed, I have an after market electronic ign. kit installed, but problem still exists with old points installed. Resister wire has not been changed but I don't know if they go bad over time? Engine runs great out of the water. When it hits the water and motor gets under load then it bogs down greatly after more than about 10 knots. Coil seems to get extremely hot also. Is my alternator/regulator going bad? A short circuit in the ignition?? Thanks for any advice and input.
 
Hello all,
New member here.
I am having the same problem as the OP. Low voltge at coil after engine gets hot. I can hook 12 volts directly to the coil and it runs great,until the coil overheats. Can a resistance wire go bad? How can I fix this? I see this problem many times when I search but nobody posts the answer.
Thanks in advance
 
I thought so too, at first. I installed a switch on my dash when it first started acting this way. the switch puts full voltage on the coil. When it tries to die I hit the switch and it comes back to life. This has kept me from having to be towed. When it dies out, voltage at the +side of the coil is about 8 volts. It seems like the resistance wire gets more resistant when hot. I cannot find a replacement for it, even if it is the problem. I can find this problem all over the internet but nobody comes back and posts the solution.

1990 OMC 4.3
New: Points, plugs, condensor, cap, rotor, coil, fuel pump, carb rebuilt in 2010. Replaced alternator with another used one two weeks ago. No change.
 
If your engine runs great with 12V to the coil, but won't run with 8 or 9V, you need a tune up of the ignition system. I see you have a bunch of new parts, but are the plugs gapped correctly? Are the plug wires good?
Have you done a compression test? That's the first step.
Your boost in spark energy could be masking another issue like low compression.
 
How old are the fuel supply lines? If they have not been replaced recently with alcohol resistant lines, there is a strong possibility that the innards of the lines are collapsed or otherwise deteriorated. You cannot see this just by looking at the lines. Be sure that you have good open flow from tank to carb.
 
Still fighting this. Fuel lines were replaced a couple of years ago. Doesn't look like a fuel problem. When it starts dying I flip the ignition bypass switch, putting 14 volts on the coil, and it runs like new. Release the switch and it dies again. I ran new wires to the ignition switch, and from the switch back to the resistance wire. Still does the same thing. I checked ground resistance straight to battery from distributor and measured .1 ohm. Not sure where else to turn. How about electronic ignition kits? Any reccommendations? Anybody know the part number for the Pertronix kit?
 
skier-24 said:
Still fighting this.
Click to expand...


Hello, I just regestered on the forums and I see I am not the only one with this very same issue.
1988 Bayliner with the 3.0 OMC motor. I bought the boat last spring but I have had several boats over the years.
My issue is similar, the engine starts and runs for about 20minutes then starts to act up misfire and stall if I back off on the throttle, then will not idle, hard to start etc.
I have installed new wires, cap, points, condensor, coil, plugs, fuel filter, rebuilt carb, all done last season in an attempt to solve this problem.
Now that spring is here, I would like to get this resolved so that I can use the boat a bit.
Today, I pulled all the fuel lines and drained then into a clear jar, pulled the fuel gage sender and syphoned about 3 gallons of fuel fronm the bottom of the tank and let it all sit for a few hours. I see no evidence of old nasty gunk or water. I then ran the boat on an external tank with brand new high test and was able to duplicate the failure here in the driveway with the engine running on Muffs.
The engine is not overheating, and I am now convinced that it is not a fuel issue.
The way I see it, I have now cut the possibilities in half as I am not looking at fuel issue.
Now I guess the next stem is to check compression and then try to understand the whole coil and resistor system. I pulled all 4 spark plugs they all look normal.
 
My compression is good on all six cylinders. When mine acts up, I connect 12 (14) volts to the coil, and the engine runs perfectly. But I can't leave it like that.
 
If your only seeing 3.5 volts at the coil battery terminal when the engine is running then yes you have a low voltage problem. Probably a connection issue where the resistance wire connects in the harness. Those wires can be a 2 to 3 feet long and are usually easy to identify as the insulation is much different than the regular wires in the harness due to the heat that they build. The only way I have been able to repair them is to pull the harness out of the machine tear it all apart so you can see every thing and then tug gently on the wire itself to make sure it is not broke inside the insulation. If that all checks out then make new connections on the ends. Then you want to try it before taping it all back up to make sure the issue is resolved. Major pain as a rule to do. I have found it is usually more cost effective for a customer to run a new wire from the ignition switch to the coil and bypass the resistance wire. Then install a heavy-duty external ballast resistor on the coil and that becomes the new resister for the system. Normally I just pull the wire loose at the key switch and tape it so it can not cause an issue. The coil end I usually leave connected that way the bypass circuit for starting will still function as it should. If you want to convert to electronic ignition you probably still need to run a new wire as most of those systems that I have been around want battery voltage at the coil when the engine is running. Normally running a resistance wire should show you about 8 to 10 volts at the coil. What they are doing more than anything is cutting the amount of current that the points have to switch to keep the contacts from burning up so fast.
 
ihc1470 said:
If your only seeing 3.5 volts at the coil battery terminal when the engine is running then yes you have a low voltage problem. .
Click to expand...

The OP was from 2014 and they never followed up. The newer posts have similar issues but I do not know if the data on the coil voltage is as wacky as the OP.
I am continuing to investigate my issue. I have ruled out fuel issues and my next step is to do a cold compression test followed by a second compression test as soon as the motor starts to stumble. I also plan to check coil cold and on stumble.
 
Well, I put a new coil on and the engine is running fine so far. The previous coil, only used for about a year, must have gone bad. The true test will be when I take it to the lake Thursday.
 
skier-24 said:
Well, I put a new coil on and the engine is running fine so far. The previous coil, only used for about a year, must have gone bad. The true test will be when I take it to the lake Thursday.
Click to expand...

I hope this solves your issue!
Please follow up to the thread so that we can gain from collective experience. let us know if it is fixed for certian.
if you can, please let me know what is the voltage that you read from the + side of the coil to the battery negative. I am wondering if you read 12 volts with the key in the run position or something around 9 volts or less.

I am trying to undersytand the how this all works. So far, what I think i know is that the + side of the coil is fed full battery voltage when the key is in the start position, then, when the key is released to the run position, the + side of the coil is fed a resisted voltage that is less than full battery voltage.

I have not found information on exactly what the correct voltage is when in the run position.

Thanks
 
With the engine idling, I was reading about 9.5 volts on the + terminal and about 4.5 to 5 volts on the - terminal. Not trusting my cheap meter, I double checked with my Fluke 87 and read about .2 volts more. Close enough.

The coil is fed full voltage, about 10 volts while cranking, by way of the starter solenoid. When you release the key, to the run position, it gets power from the ignition switch through the resistance wire. On my engine, the resistance wire runs from the alternator "S" terminal to the coil "+" terminal. The wire from the ignition switch is terminated around the middle of the resistance wire. The whole bundle of wires was wrapped in tape making it difficult to determine where the junction was.

Incidentally my boat had been hard to start for years. I could crank and crank, but I felt like it was not firing until I released the key to the run position. Since troubleshooting and rewiring over the last couple of years, it starts immediately, better than when it was new.
 
Last edited:
skier-24 said:
With the engine idling, I was reading about 9.5 volts on the + terminal and about 4.5 to 5 volts on the - terminal. Not trusting my cheap meter, I double checked with my Fluke 87 and read about .2 volts more. Close enough.

The coil is fed full voltage, about 10 volts while cranking, by way of the starter solenoid. When you release the key, to the run position, it gets power from the ignition switch through the resistance wire. On my engine, the resistance wire runs from the alternator "S" terminal to the coil "+" terminal. The wire from the ignition switch is terminated around the middle of the resistance wire. The whole bundle of wires was wrapped in tape making it difficult to determine where the junction was.
Click to expand...

Thats great information! Thanks.
Please let me know how your trip to the lake goes and if your issue is "fixed".
Good Luck!
 
The boat ran fine at the lake Thursday. Evidently, the coil, I replaced in 2014, was the culprit. First coil lasted over 20 years. That is why I couldn't believe it was a coil problem. I think I will carry a spare coil from now on.
 
WOW! that is good news, I am glad that you are up and running.
I also bought a new coil yesterday, from the Marina, The coil that is supposed to be correct, says it requires external resistor, just like the coil that is in the boat that I installed last year.
with new coil or old coil, I get around 12v on the positive side and about 10.5 volts on the negitive side with the boat running.
So I am still stumped.
 
Your volt readings sound high compared to mine. Do you still have an external resistor, that is, the resistance wire? What voltage is your alternator putting out?
 
skier-24 said:
Your volt readings sound high compared to mine. Do you still have an external resistor, that is, the resistance wire? What voltage is your alternator putting out?
Click to expand...

On my positive side of the coil, I have 2 wires, one that appears thicker than the other, the thicker wire is a purple color with a stripe, the other is a redish. the heaver wire runs down to a lug on the starter motor and the other runs to the switch. It all looks quite stock and normal compared to the pictures I have seen on line. I was thinking that checking the alternator is on the list, along with compression test and to check the dwell on the points. A much needed rainy day here so a welcome break from fussing with this motor but this week, I am planning on taking the boat down to the river, doing some more testing cold, then getting the motor to the failure point (running rough) and testing the voltage and compression at that point.

Thank You for replying. I will follow up to this thread as I get more info or if for some reason I am able to solve this. Any more ideas will really be appreciated!
 
finnyct90 said:
On my positive side of the coil, I have 2 wires, one that appears thicker than the other, the thicker wire is a purple color with a stripe, the other is a redish. the heaver wire runs down to a lug on the starter motor and the other runs to the switch. It all looks quite stock and normal compared to the pictures I have seen on line. I was thinking that checking the alternator is on the list, along with compression test and to check the dwell on the points. A much needed rainy day here so a welcome break from fussing with this motor but this week, I am planning on taking the boat down to the river, doing some more testing cold, then getting the motor to the failure point (running rough) and testing the voltage and compression at that point.

Thank You for replying. I will follow up to this thread as I get more info or if for some reason I am able to solve this. Any more ideas will really be appreciated!
Click to expand...


Today, I intalled a new coil and took the boat down to the river and let her run on the ramp. It ran for an hour without starting to skip, miss and run poorly and was still running good when I shut it off. I still have 12 volts on the positive side of the coil and around 10 volts on the negitive side. previously, the boat would start to run real bad within 25 minutes. So I think the coil was bad or the coil is a casuality of what really is wrong.

I am still searching for why I have high voltage when running, and I do not expect that I have solved anything yet.
 
If the coil is getting hot put a ballast resistor wire to coil posative. If your running a electronic ignition that is using coil pos just splice the ignition and key on to the resistor and connect the resistor to the coil. I didnt read back do you have points in the distributor?
 
kimcrwbr1 said:
If the coil is getting hot put a ballast resistor wire to coil posative. If your running a electronic ignition that is using coil pos just splice the ignition and key on to the resistor and connect the resistor to the coil. I didnt read back do you have points in the distributor?
Click to expand...

Thanks for the reply.
This is a 1988 OMC 3.0 and it has points in the distributor. I do not see any signs that the wireing has been fooled with, it appears to have the stock 2 wires on the Positive side of the coil, one runs down to the starter, one disappears into the harness. I suspect that if I do not figure out why I have 12 volts at the coil when running, I will be in bad shape soon with either burnt points or another bad coil.

I guess I need to understand how much resistance is needed to bring the voltage down to near 9 volts and what could cause the stock resistor wire to not do its job.
 
Do you have a schematic? It may have a start circuit similar to the old cars when you turn the key on you should have ballast voltage then when you turn it to start it provides battery voltage at the coil for quick starts. It can be accomplished in several ways but most common is off the start solenoid.
 
kimcrwbr1 said:
Do you have a schematic? It may have a start circuit similar to the old cars when you turn the key on you should have ballast voltage then when you turn it to start it provides battery voltage at the coil for quick starts. It can be accomplished in several ways but most common is off the start solenoid.
Click to expand...

Yes, from what I understand, that is exactly how it works.
I have a manual and I did trace out the wire that heads for the starter, I am taking that to be the "start" feed to the coil. The other wire (they are crimped to the same end at the positive coil) heads into the wire harness and I am guessing that that wire is the resistance wire. It should be the wire that supplies power to the coil when in the "run" position. From what I read, that wire should be a "resistor" wire. So now I think I need to see if it is actually adding resistance? I was thinking of doing a test by running a wire of proper resistance from the run side to the positive side of the coil and see if it has an effect. I just am not sure what the resistance should be.
I really appreciate the replyies and I intend to follow up on this post so that others with the same problem might gain from it.
 
I had the same issue with my volvopenta and just spliced a resistor going to the coil and she starts just fine cold and runs like a top. The coil barely gets warm now and plugs are burning nice and clean.
 
kimcrwbr1 said:
I had the same issue with my volvopenta and just spliced a resistor going to the coil and she starts just fine cold and runs like a top. The coil barely gets warm now and plugs are burning nice and clean.
Click to expand...

I am tempted to do the just as you suggest. I am still working through the issue, my resistor wire (stock) appears to be intact and I am afraid that all I would be doing is dealing with the symptom but not the root problem. Maybe the stock resistor wire is corroded in the harness and that's all it is and if so, adding an external resistor is the fix.
One thing about this boat, I am probably the 3 owner and someone, ( previous owner) liked to have all sorts of electronic dodads and gadgets. When i got the boat last summer, it featured an hour meter, an old school VHF radio, a fish finder, extra cabin lights, 2 bilge pumps and a dual battery system. All this stuff was wired poorly, wires just twisted to existing under dash wires, a couple connections were taped over using band aides. Today, I spent a couple hours removing all that McGiver junk and restored the battery system back to one good deep cell and stock positive and ground. I now have a milk crate stuffed with gadgets and about a 100 feet of wire.
i guess I am wondering if all that junk could be causing or caused stress on the electrical system and may have been the root cause. I hope to take it down to the river this week and run it while testing, and trying an external ballast resistor to see what effect it makes.
Thanks Again
 
Back
Top