The Ghost in the Machine - voltage drop in the ignition system?

Can anyone help?  I bought a 1966 38 Commander Sport Fisherman back in October.  The boat had been refitted with Twin rebuilt Chrysler 360s about 7 years before I bought it.  After the engines were installed, the boat was water tested, then removed from the water for cosmetic work.  It subsequently sat idle for the next 7 years.  Needless to say, I got a good deal from the marina I bought the abandoned Commander from.  After purchase, I had it moved to my local marina yard and began the process of getting it water worthy again.  All was going well until I couldn't get spark from the coil in the port engine.  Here's what I've done:

1.  I removed all the spark plugs and put a few drops of Royal Purple in each hole.

2.  I turned over each engine by hand.

3.  I compression tested all 16 cylinders.  All tested well.

4.  I changed the oil to new Royal Purple.

5.  I replaced all the spark plugs and wires.

6.  I replaced both fuel pumps and filters and all the fuel lines from the tanks to the carbs.

At this time, I test fired both engines.  

The starboard engine fired right up and purrs.  

The port engine had fuel leaking out of the carburetor in several spots.  To save time, I bought a new, tested, Edelbrock 4 bbl carb and replaced the original.  The only difference between the carbs is the new has an electric choke which I wired directly to an unused switched fuse.

Then I test fired the port engine again.  NO SPARK from the coil.

This is when things got interesting.  Since that time I have tried the following:

1.  New cap, rotor and magnetic pick-up (properly gapped).

2.  New ballast resistor.

3.  New Coil.

4.  New solenoid.

5.  I broke out the wiring diagram from the M360 and from the mallory magnetic pick-ups and made sure everything was wired correctly.  I found a couple discrepancies and corrected them with no results.

6.  I have tested voltage at every location I think of and here's the quandary:

        When I disconnect the ignition wire from the coil I get 10.5 volts to the wire with the key in run and 12.5 volts when cranking.  If I reconnect the wire, the voltage to the positive post on the coil is about 3.8.  If I disconnect the wire from the negative post of the coil that runs to the ignition module the voltage on the positive side jumps back up, but with that wire disconnected the engine won't crank at all.

So, I replaced the negative wire to the ignition module with a brand new 14 gauge wire thinking it was causing resistance.  No change.

So, I tried taking the ignition module off of the starboard engine (that runs so nicely) and putting it on the port side.  No change.

So, I tried getting a high powered cranking battery and blasting it with amperage hoping to overcome the voltage drop.  No change.

I've run this by a few mechanic friends and nobody can figure it out.

Has anybody else ever run into a mysterious voltage drop in the ignition system?  If so, did you figure it out and how?

Or, does anyone have any suggestions or troubleshooting tips?

Thanks,

Baron

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Baron,

From your description I think your starter solenoid or solenoid's are getting a ground thru your module in the distributor. Try removing the wire from coil to module and ground your solenoid with a jumper to the neg batt post. 

Thanks Dan!  I'll try that and let you know how it turns out.

Dan Stokely said:

Baron,

From your description I think your starter solenoid or solenoid's are getting a ground thru your module in the distributor. Try removing the wire from coil to module and ground your solenoid with a jumper to the neg batt post. 

Did you try swapping the coils? Your brand new coil could be no good.

Good thought Nat, but I did try that, no luck.

Nat Brady said:

Did you try swapping the coils? Your brand new coil could be no good.

Dan,

I was thinking about your suggestion and had a question.  When you say "module in the distributor", are you referring to the magnetic pick-up module or the ignition module?  Also, which post of the solenoid should I run the jumper off of?  It has the positive connection from the battery, an outbound positive to the starter motor, an outbound positive to the ballast resistor and an outbound positive to the coil.  Are you suggesting that I ground off of the positive connection to the coil?  I just want to make sure I'm trying the right thing.

Thanks,

Baron

Dan Stokely said:

Baron,

From your description I think your starter solenoid or solenoid's are getting a ground thru your module in the distributor. Try removing the wire from coil to module and ground your solenoid with a jumper to the neg batt post. 

Baron,

I am referring to the grounding of the solenoids, Some have ground terminals, and some have metal cases that are grounded, either way, I think the reason your starter doesn't work when you disconnect the wire from the coil to the module, is the starter solenoid has lost its source of ground, causing it not to work. Your starter system should be separate from your ignition system. The only connection between the starting system and the ignition system is a wire that is powered with battery voltage from the starter to the coil only when the starter motor is cranking.

Did you feed the electric choke from the ignition side of the coil? That wont work. Simply disconnect it and see what happens. If not clean all terminals and make sure there are no shorts to ground. A simple short to ground from a hot manifold and melted insulation had me pulling my hair out. It caused similar electrical issues on my 360.

Hi Baron:

Just a thought...Of all the things on your list I didn't see that you didn't try bypassing the ignition switch to start your engine?  

Best Regards,

Lewis 

I've seen faulty ignition switches cause mysterious voltage drops like you describe. The switch contacts get corroded and will pass enough current to make a decent reading on just a voltmeter alone, but when the system load is applied the switch can't pass enough current and the voltage drops like a rock. One of the best tools a diagnostician has in his tool box is about a 3 foot chunk of #14 (or #12) wire with an alligator clip on each end. Why don't you make one of these up and supply the coil positive with 12 volts directly from the battery? Cheap, and it's easy and doesn't take long. BTW, although a little foggy from your description, I am assuming that this engine is turning over in the key start position ? PS-- If indeed this test works, bear in mind that corrosion or loose contacts anywhere in the coil primary circuit could be the culprit. It's just that the ignition switch is the most likely suspect.

sometimes difficult to determine what is going on with the new multimeters. Just because it says 12 or 12.5 volts doesn't mean it is getting anywhere near the current required. It is a phenomenon electricians call phantom or shadow voltage, enough for a digital multimeter to see but no umph (current) behind it. An old simpson meter would probably show a different story. I agree with Dick, get out your jumpers and basically hot wire the engine to start. Or if you have the original gauge package that came with the Chryslers swap out the engine gauge plugs and run the engine off the other engines gauge and key switch. Wish I was there with a meter! 

What about your tachometers. If I remember correctly, Trojan boats with 360's had issues with tach's or the wiring to the tach. The signal came from coil. Not sure if this applies. Just throwing it out there.

Thanks Kevin,

This afternoon, I plan to head over and wire a new ignition switch in, bypassing the original.  If I'm getting too much resistance somewhere between the battery and the coil, I'm hoping that will fix it.  That's entirely possible since we have 2 ignition switches (helm and fly bridge) and 2 bus bars between them.  I'll update after I've tried it.

Kevin McKinnon said:

sometimes difficult to determine what is going on with the new multimeters. Just because it says 12 or 12.5 volts doesn't mean it is getting anywhere near the current required. It is a phenomenon electricians call phantom or shadow voltage, enough for a digital multimeter to see but no umph (current) behind it. An old simpson meter would probably show a different story. I agree with Dick, get out your jumpers and basically hot wire the engine to start. Or if you have the original gauge package that came with the Chryslers swap out the engine gauge plugs and run the engine off the other engines gauge and key switch. Wish I was there with a meter! 

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