multiple coils going bad

[piasajake]

I have a '85 mercruiser 140 with a standard points ignition. Over the years I have had trouble with coils going bad. Years ago I was told to remove the existing resistor wire and replace it with a regular wire and install a coil with an internal resistor. That coil setup worked for a while but eventually went bad too. I probably went thru 3-4 coils over the seasons that it was used. I thought I would try going back to the original setup and installed a new resistor wire, coil, plus a new distributor with new points, condenser, cap & rotor. It ran great for several outings and then the coil crapped out again. It ran very rough all of a sudden and would hardly start and then would not start at all until it cooled down. I switched out the coil with a spare one I had and it started and ran fine. Then I switched back to the original coil and was very hard to start and ran rough. I also put a timimg light on all the spark plug wires and they all showed erratic misses while the engine was running with the old coil. Could anyone give me some ideas of why I keep having coils go bad or what I can troubleshoot for possible causes? Any suggestions or ideas would be greatly appreciated.

 

[Haut Medoc]

Re: multiple coils going bad

I would check to see how many volts I had at the+ side of the coil with the key on first.....If you have 12v your resistor wire is not working....It should be something like 7-9 volts.....JK

 

[xtraham]

Re: multiple coils going bad

use normal wire and install a ballast resistor,

 

[bruceb58]

Re: multiple coils going bad

What dwell are you running at? What is the voltage at your coil? When your coils fail is it the primary windings that are opening up?

Too wide a gap on spark plugs and faulty spark plug wires can also hurt coils because you end up causing a higher current to flow through the secondary of the coil.

Heat and vibration are also very hard on coils. If your coils is not mounted in it's original position and it is close to the exhaust manifold, it might be getting too hot.

 

[piasajake]

Re: multiple coils going bad

Finally had some time to do some testing. From the suggestions and looking at other posts, from what I can see everything is wired correctly and the voltages and resistance levels seem to be in the acceptable range. The coil is also mounted in the original position. The resistor wire does get fairly warm or hot with the key on and the engine not running. I don't know if this matters or not, but my new distributor is a Prestolite instead of the Delco style.

The only other thing that might be the cause is what bruceb58 said about the bad wires and spark plug gaps. It has been several years since I have replaced the wires and possibly the plugs. I guess I will try new wires, plugs, new coil, and replacing the resistor wire with a regular wire and a ballast resistor. I am also considering getting a new alternator and a new starter since I have been cranking on it so much when the coil went down.

If there are any other things I can check or other suggestions to why my coils keep going bad, your comments would be appreciated. Thanks for all the suggestions.

 

[Dunaruna]

Re: multiple coils going bad

[colour=blue]How did you do the tests? Can you post results?

The dwell would need to be WAY out to eventually effect coil longevity, there would definetly be other symptoms associated with dwell/timing problems.

Let's see some figures on the resistor wire test.

 

[hoot]

Re: multiple coils going bad

jake, what type of coils are you having trouble with? automotive type, mercruiser brand, oil filled, epoxy filled? i replaced an old one this year with one that was made in china. as i was tightening the wire nut, the plastic around the stud broke away. i am having a similar problem every other year or so and am interested in what your outcome is. i am also considering going pointless with a new coil and conversion kit.

 

[bruceb58]

Re: multiple coils going bad

Exactly!

The dwell would need to be WAY out to eventually effect coil longevity, there would definetly be other symptoms associated with dwell/timing problems.

 

[piasajake]

Re: multiple coils going bad

hoot,
My last coil was a Mercury/Mercruiser marine coil with a new external resistor wire. When this one went bad it was different from the ones in the past. It went really bad all of a sudden when I was cruising at very low speed. The other coils that went bad before started cutting out and running rough, mostly after running the boat hard while pulling a tuber or skier, but at least still ran for a while. My last coil failed the worse I have experienced with all my replacements (at least 4). It won't even hardly start being cold and will run rough if it does start and die fairly quickly. If I replace it with a spare coil, it starts and runs fine. I have also used automotive coils with internal resistor when I removed the resistor wire years ago. They also went bad after a period of use, but would still run for a short period after they cooled down. All the coils I have used were oil filled.
I also had the cam, timing gears, and timing chain replaced last year as well.
I guess I need to get my parts and try it out while I still have a little time left this season. I might not be able to see how the new setup with the ballast resistor holds up until I get to use it more next season.

bruceb58, would you recommend getting rid of the points and switching to a electronic ignition and if so, would it eliminate my problem?

Any other suggestions or comments are appreciated.

 

[bruceb58]

Re: multiple coils going bad

Depends on what is causing your problem. Points are very reliable and, if properly adjusted, have really no performance disadvantage over the electronic points.

bruceb58, would you recommend getting rid of the points and switching to a electronic ignition and if so, would it eliminate my problem?

Did you ever check your dwell like I asked in a previous post with a dwell meter?

 

[piasajake]

Re: multiple coils going bad

To be honest, I'm not sure I know how to check the dwell. I set the points with a feeler guage and adjusted the timing with a timing light. Is it possible to check the dwell with a multimeter?

 

[Haut Medoc]

Re: multiple coils going bad

No, you need a dwell meter...
You need to set the dwell, then the timing.......JK

 

[ziggy]

Re: multiple coils going bad

You need to set the dwell, then the timing.......JK

because dwell effects timing......

 

[bruceb58]

Re: multiple coils going bad

Only if your meter can measure "duty factor"

Is it possible to check the dwell with a multimeter?

 

[hoot]

Re: multiple coils going bad

please help educate me on adjusting dwell. i understand what it is and that you need a meter to set it. and on some distributors there might be a door to lift and adjust the dwell. on the older systems, once the point gap is set and the distributor set down, the only way to reset is to remove the cap. if the point gap is within the specified range, would the dwell angle be acceptable?

 

[bruceb58]

Re: multiple coils going bad

This what I do...I run the engine and measure the current dwell with a dwell meter. I then take off the cap and crank the engine to see what the dwell is that way. I note what that offset is and set the dwell with the cap off plus or minus the offset. I put the cap back on and measure again to verify.

No marine distributor has a door on it. You are referring to the old automotive GM caps.

 

[piasajake]

Re: multiple coils going bad

I don't know if it would do any good to check the dwell at this point. At the time of the coil failure I checked the gap adjustment on the points and moved them from the setting they were running at when the coil failed. I will be sure to set the dwell when I replace the coil. I do have a old coil that it will run with. Should I set the dwell with the old coil or wait until I get the new one? I am also probably going to replace the plugs and wires too and possibly the starter and alternator. It also sounds like it would be a good idea to replace the resistor wire with regular wire and a ballast resistor. Any thoughts?

 

[LuckyPenny]

Re: multiple coils going bad

I had the same exact problem. After several coils, new plugs and wires, new points and condenser we finally traced the problem back to the dash. Somewhere along the line someone installed a new Amp meter, and took the lead to in ing side of the starter switch instead of the Batt. In effect, the coil was getting the full output of the alternator. Not very good for the ing system at all.

 

[bruceb58]

Re: multiple coils going bad

Lucky,

I am sure you are talking about a voltmeter and not an amp meter. Your voltmeter should be hooked to the ign terminal and should have zero affect on the voltage to the coil since that is tapped off later.

 

[bruceb58]

Re: multiple coils going bad

The dwell value is independent of which coil you have. It's up to you to change out the resistor wire to a ballast resistor since they both do exactly the same thing.

Pick up a dwell meter. Thay are only around $35 and may be less at Wall Mart.

I don't know if it would do any good to check the dwell at this point.