grounded the alternator hot post, now no spark

[NHGuy]

I feel pretty stupid. I know enough to power down the engine while working on it and I still messed up. I touched the main post on my alternator while assembling my power steering and now I have no spark. This was done while the key was off.

There's no spark now, I went as far as disconnecting my shift interrupt and then checked the output circuit. It has battery voltage.
But there's no fire at the plugs, and there was before this muck up.

I have the manual and I was going to next test the excitation circuit, and then the sensing circuit.
After reading the electrical diagram it appears that the only pieces in the line of fire are these.
I happen to have a new regulator/brush assembly. And I bought a new rectifier bridge this week in case I need it.
What else do I check, anything?

 

[achris]

Alternator circuits (sense and excitation) don't affect spark. And are not running while the engine is cranking anyway. It's possible you spiked the ignition module. Go through the TB-IV/V troubleshooting chart and see where it leads you.

I assume you are cranking ok, and that you have checked for power on the + terminal of the coil.

Chris..........

 

[NHGuy]

On the other forum AllDodge suggested checking for the 90 amp fuse on the starter post, but I don't see one on my engine. If it's there I sure don't see it, and the starter works.

It does have a breaker on top of the motor, that is good. And the starter still works from the helm or the remote solenoid.

The ignition is Davis Unified (DUI) which is just a marine rated improved version of the 80's era GM HEI. It's new this year and I ran the engine in my yard with it before installing to the boat.

I followed their test process and found the primary coil impedance was NG, infinite.

Their instruction page says I could have run a regular HEI coil so I grabbed one at the parts store.

Just in case of questions I decided to ohm out the new coil before removing the packaging, it failed too.

At that point I was out of time so I packed it and returned the replacement part. I have another meter, so I'll check the DUI coil with it before I contact DUI.

I'll put a test light on the ignition powered circuit (purple) when I crank to see if that gets voltage. At last check it was dead with key on, but I hadn't tried it with the start circuit running.

I'm also going to try powering the engine from the engine mounted cannon plug as I do to run it on a stand. That would eliminate the wiring to the helm. It might get some results on 31 year old boat with a 21 year old harness.

Hope it's only the $55 coil.

 

[Scott Danforth]

Doubt its the $11 coil, most likely the $9 ignition module. If you pay more than that, you are wasting money in HEI parts

Its almost never the coil

Check voltage at the purple wire at the coil, you should have batt voltage with the key on

If you have voltage there,

Align the motor at tdc so your rotor is pointing to cyl 1, put timing light on cylinder 1

Then unplug the ignition module from the coil

take a wire to the tach terminal and rapidly touch a good ground and your DUI HEI coil should be firing every time you pull the wire off ground

if not firing, check the button spring under the coil and retest

If #1 cyl is firing, then most likely the $9 ignition module is bad

 

[Scott Danforth]

If you have no voltage at the purple wire, you have no ignition power. Fix that issue

 

[NHGuy]

Thanks, I love it when people distill it down to the basics!

 

[NHGuy]

Just in case any one else comes across this post and goes to follow the process. I'll do one thing differently from Scott.

I'll use a test light on #1 as opposed to a timing light.

If that's a fail I'm sure he will come back and update us.

BTW, when I checked at the ignition there was power to the purple "BATT" terminal with key on. So one less problem.

 

[NHGuy]

So. as is typical. Coil tested again with correct ohm scale and unplugged from engine harness - was good.
I called Davis Ignition and he thought it would be the module. It was.
I'm back in business.
I hope if someone else does the same dumb thing I did they can learn from my mistake.