Troubleshooting a coil

[ErikF]

Hello,

I'm working on a Mercruiser 165. The motor has been sitting a long time and I'm working to get it going again. Right now I'm trying to get the ignition system working. I found the old coil to be bad and replaced it with a new one. However I still cannot get a spark, with the key in the run position I have a steady 3.7VDC at the coil (I know this is a little low, problem?) With the key in the start position and the engine turning over I have ~10VDC (same voltage at the battery).

Any ideas? Do I have another bad coil? I checked the new one with my fluke and it's .1ohm off on the primary (1.5 vs. spec of 1.4) however I can't find a tolerance for variance so I'm not sure if it's bad or not on this alone.

Comments, ideas?

Thanks,

Erik

 

[Bondo]

Re: Troubleshooting a coil

Ayuh,... The Points fire the coil,...

Replace the Points...

 

[jerryjerry05]

Re: Troubleshooting a coil

The coil should have a resistor built in if it's off the shelf.Merc has a resistor wire in the system(maybe)
Should have 12v in and 9v out of the coil.12v to points and they'll burn. Check the battery for charge.
File/replace the points.Change the condenser/rotor.
Dwell about 29+/- 1J

 

[fourfather]

Re: Troubleshooting a coil

removed

 

[Eric 3.7LX Alpha 1]

Re: Troubleshooting a coil

I hope you don't mind me hijacking your thread, but I have a similar situation. I was given a boat in bad shape and while fixing it up discovered the alternator was making 17 volts (sometimes more), so I ordered an alternator. The coil on this boat says right on it that it needs a ballast resistor but there isn't one present, so knowing what excess voltage does to points, I filed and reset them (but I didn't buy a ballast resistor yet). Before the alternator arrived I got far enough on the project to give her a test on the water. If I run her wide open for 4-5 minutes the RPMs will fall off sharply and then she'll die. If I wait till she cools off, she'll start back up and run great for 4-5 minutes. Then the process repeats itself. When running wide open the volt meter is buried (I didn't check it with my diagnostic volt meter). BTW, this boat will idle for long periods without any issues.
I should add that this is a 1975 Mercruiser 165 (straight 6 Chevy).

Here's my question: do you think I was overheating the coil with the excess voltage causing the problem described or should I look elsewhere?

Thanks,
Jesse

Announcement: -------------Please DO NOT reply to old threads or hijack existing threads. Old threads of a technical nature are like a library book, Do Not write in them.

How To: Troubleshoot a Points Ignition System
http://forums.iboats.com/showthread.php?t=335407

From the Adults Only sticky at the beginning of this forum^^^

 

[fourfather]

Re: Troubleshooting a coil

My apologies, I removed the question and started a new thread.

 

[ErikF]

Re: Troubleshooting a coil

Thanks everyone for the replies. I realized soon after I posted that most of my problems were stemming from never having worked on an ignition system with points before or really any automotive gas engine ignition (I work primarily on diesels so this was new territory)

And as a result I was misunderstanding the wiring schematics and conducting my test opposite of how I should have.

In short the coil was good, I was just testing it wrong, the points were good but needed adjustment, I got everything sorted out and the engine started right up and ran great!

Thanks Everyone,

Erik