Mercruiser 4.3 Crank But no Start (spark issue)

[ESully94]

Hi everyone, new to boat life and new to the forum. I recently bought a 1990 (old I know, but in great shape) maxum 2100 with a mercruiser 4.3. First few days of having the boat it started right up never an issue. One day I forgot to turn off the radio when covering the boat (it was raining really hard) and it drained the battery. Was anticipating it to be a simple battery swap but that was not the case.

Battery was replaced, then bolts on starter snapped. I ordered and replaced the starter. I have also replaced the solenoid, ignition coil, distributor cap and rotor, spark plugs and spark wires with no luck. When I check the spark at the distributor, I get one initial really strong blue spark when cranking. After the initial spark, there are no more sparks until I reset and recrank.

From reading around the forums like a mad man, I came to the conclusion the problem could either be a bad ignition module, possibly a shift interrupter? Perhaps something else I am overlooking?

All 4 wires that come off the thunderbolt IV ignition module have power which go to the coil. Purple is good, grey is good, white with red stripe is good. Getting very low readings on the white with green stripe. Pretty sure this wire controls the feed being sent to the coil in order to generate sparks in the distributor.

Any help would be greatly appreciated as I am ready to bring it to a local marina and call it quits. Money is not the issue and have no problem bringing it to a professional. I just wanted to sort the issue myself so I am knowledgeable about my older boat and know how to service and maintain it myself

[mmwjr]

So does the engine crack over when trying to start? Why did the stater bolt break off? Is it possible water got into the engine? I’ve not heard of a case where spark is there but goes away after a few cranks, how are you verifying this?

[ESully94]

The main cap in the center of the coil was removed, and an insulated screw driver was used to check the spark output. From the main plug wire, there was one initial solid blue spark and is gone after legit one spark.

I couldn’t tell you how the starter bolts broke, there is no mount or brace for it, and the starter was dated from 2011 so I’d imagine corrosion on the bolts.

Engine does not crack over. Starter engages, solenoid is working and everything. Just no spark to fire it over.

Spark plugs when I remove them show no signs of firing at all. Completely clean when I pull them out.

[mmwjr]

With the spark plugs out can you spin the engine over by either hand or the starter?

[ESully94]

I also forgot to mention that I was using a light tester on the electrical connectors, and found that all of the wires coming from thunderbolt IV ignition module all carried strong currents aside from the white and green wire that goes from ignition module to the distributor itself. Leads me to believe the coil is not getting ready power, and therefore cannot generate a spark to be transferred into the distributor.

[ESully94]

Yes the engine spins plenty. If I had spark it would fire right up. Just never achieving ignition.

[mmwjr]

Ok, then it’s either the ignition sensor in the distributor or the module which is no longer available. You can find used ones on eBay but it must be for the V6.

Worst case is get an aftermarket marine distributor which is a complete ignition system with coil. Mallory, Sierra are two such suppliers.

[ESully94]

How would I be able to tell which it is? Could I run a Hotwire from the battery to the coil to see if it is indeed just not getting power?

[ESully94]

Why would the aftermarket part be worst case though? Wouldn’t it be better to bypass a part that is no longer available??

[ESully94]

Could you perhaps share a link to the aftermarket part you speak of? Will likely go that route, as I’m in this mess right now I’m the first place from some else’s used stuff lol. New to the boating world and boating repairs, so I wanna make sure I buy the right thing here!

[mmwjr]

Originally Posted by ESully94

How would I be able to tell which it is? Could I run a Hotwire from the battery to the coil to see if it is indeed just not getting power?

Running 12V to the coil is just going to ensure the ignition system is getting power and will not compensate for a bad, sensor or module.

[mmwjr]

Originally Posted by ESully94

Why would the aftermarket part be worst case though? Wouldn’t it be better to bypass a part that is no longer available??

There is no bypassing a bad ignition sensor or module. Aftermarket replaces everything.

[mmwjr]

Originally Posted by ESully94

Could you perhaps share a link to the aftermarket part you speak of? Will likely go that route, as I’m in this mess right now I’m the first place from some else’s used stuff lol. New to the boating world and boating repairs, so I wanna make sure I buy the right thing here!

I’m working now but will provide a link later.

[ESully94]

Awesome thank you so much!!

To clarify, with this aftermarket distributor/coil, I would not have to change the thunderbolt IV module correct? The new distributor takes that module completely out of the equation?

[mmwjr]

Originally Posted by ESully94

Awesome thank you so much!!

To clarify, with this aftermarket distributor/coil, I would not have to change the thunderbolt IV module correct? The new distributor takes that module completely out of the equation?

Correct!

[ESully94]

Fantastic!! I will be eagerly awaiting the link you post and you better believe I will be paying overnight shippin lol I live on a huge lake and everyday I look at the boat and can’t go out on it kills me inside a little bit hahaha

[mmwjr]

This is the one i was referring too but not sure it's in stock at this place, all other places it's out of stock.

https://www.wholesalemarine.com/sier...YaAurnEALw_wcB

Another option but don't know anything about them.

https://www.amazon.com/Marine-Igniti.../dp/B07NGYZRH4

[ESully94]

Thanks!!

Upon further inspection, I noticed the shift interrupter switch was super corroded and actually stuck!! Cleaned and lubed it and now it’s moving freely, but not sure if I need to replace the switch as the metal arm holding the wheel on it seems to have bent a good portion. Could a shift interrupter cause no spark if the kill switch on it is engaged?

[mmwjr]

Originally Posted by ESully94

Thanks!!

Upon further inspection, I noticed the shift interrupter switch was super corroded and actually stuck!! Cleaned and lubed it and now it’s moving freely, but not sure if I need to replace the switch as the metal arm holding the wheel on it seems to have bent a good portion. Could a shift interrupter cause no spark if the kill switch on it is engaged?

Yes, that’s exactly what it does when shifting out of gear. It kills the ignition for a very short time to remove engine load on the dog clutch to make it easier to shift out of gear.

[mmwjr]

You can try temporarily disconnecting the shift interrupt switch to see if the engine will run