Weak spark, no start after bump in road 86 OMC 4.3

Ackevor

Cadet
Joined
Sep 25, 2019
Messages
25
I have been unable to get this engine running reliably since I bought it. GM 86 OMC cobra previous owner swapped points to pertronix ignition, I had it running once, changed the out drive because it was destroyed and couldn't get it running again.

Took it to the local mechanic and he said when he went to start diagnosis it started right up and to just come get it. I brought it home and sure enough it did. The boat started and ran great in the driveway. I was excited and immediately took it to the launch. Got it in the water and again no start, same as before.

What in the world would cause the bumps down the road to keep it from starting? I know I know lots of things probably.

Fast forward a year and I'm still messing with it and that mechanic doesn't return my calls anymore, no one else around me can get to it for the rest of the season...

Here is what I know or tried.
New pertronix flamethrower ignition coil because the old one was reading 2.1 ohms between +/-and 8550 ohms from center to either polarity.

When I check the voltage to the positive terminal of the coil with the key in the run position I was getting 4.5v. I know this is supposed to be 8v+ and ideally battery voltage. The only way I can get battery voltage is by removing the pertronix ignitor (1563B) red wire from the positive terminal. The moment I touch the wire to the positive terminal it drops from 12.8v to 4.5 and I can hear a hum almost.

I thought there it is! the ignitor is burned up. Took it off and tested it, works fine. It reads battery voltage without the magnet and 0 volts when the magnet is in position next to the ignitor. Unless I'm doing something wrong am I correct in thinking I should replace the ignitor since it's the cause of drop in voltage to the coil?

I feel silly thinking I need to purchase a new ignitor when it tests ok but wanted to get some input from those more experienced than I.

Yeah the springs under the plate look rough but still function.



P_20250716_180210.jpg


P_20250716_174854.jpg
 

Ackevor

Cadet
Joined
Sep 25, 2019
Messages
25
I will start testing continuity anywhere I can to check for broken wires.

Perhaps I'm mistaken, but I don't see an ESA here, it looks like 2 relays. I was going to test the ESA after work, does this setup look familiar to anyone?

As far as the voltage at the coil I am going to try a jumper from positive terminal to the positive of the battery and see if it starts. If it does but then stalls when I pull the jumper off, I think I will need a relay from the ignition switch to the coil and the battery because they forgot to bypass the resistor from the ignition switch to the coil.
P_20250716_180309.jpg
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
50,838
I personally have never had luck with the pertronix modules longer than a few months. 3 out of 3 went bad. 2 of them broken wires where they go into the unit.

easy to check for spark (before you pulled it all apart). and determine what is wrong.
 

kenny nunez

Captain
Joined
Jun 20, 2017
Messages
3,388
Petronics ignition are not compatable with OMC esa systems. The 2 relays you posted showing are actually for the power trim/tilt.
Sierra # 18-5277 tune up kit. Gap the points at .017. 1 877 663 8396. This will get the esa system working if all the limit switches are working and connected properly at the plate where the shift cable is connected.
The ignition wire that comes from the ignition switch must have 12 volts in cranking mode which bypasses the resistor wire to assist in starting. Once the engine starts there should be 8-9 volts on the same wire. The 12 volts in cranking comes from the starter solenoid.
Post a picture of the shift cable bracket where the micro switches are located.
You need to get a Genuine OMC service manual for your model #. They can be had from Michigan Motorz. Or just google it. And not one of those generic Clymer /Seeloc ones.
 
Last edited:
Top