1990 larson all american 195 4.3 confusion

[Rslavinjr]

Confused about the layout of my 4.3 mercruiser in my 1990 larson. Went to change out my exhaust risers and noticed on the back of the engine was a coil. My engine has an hei distributor so the coil, as it seems to me would be pointless. There are a few loose wires behind the engine that have eyelets on them so I would guess they were once attached to that seemingly pointless coil, but unfortunately I have been unsuccessful at locating a good wiring diagram for this engine/ boat. Even on iboats the ones that have been posted previously either don't open or don't show enough to check over everything. Does anyone have a complete schematic for a 1990 4.3 mer-cruiser with an alpha 1 outdrive. As a bonus would anyone have or know how to get a hold of a full boat diagram for this All American.
Thanks all. I look forward to your responses.

 

[tpenfield]

Serial number for the engine would help narrow down exactly what you have.

What is a pointless coil? Not sure if the issue is pointless

1990 would probably be electronic ignition of some sort. Most of the Mercruiser part websites will have an electrical diagram for the engine . . . Google is your friend. Here is a diagram from a parts website . . . but not knowing your serial number it may not be 100% accurate.
.

 

[Meames1]

I too have a 1990 Larson that originally came with the 4.3 V-6. If yours has an HEI (GM car-type) distributor, then someone has swapped it out from the original Thunderbolt IV ignition. They must have never removed the old coil. With the single-wire hookup of the HEI distributor you will be left with several loose wires that went to the original dist, and the unused module on the port side exhaust riser (unless they removed that as it's no longer needed). I have the original Mercruiser install manual at home for mine that has the wiring diagram. I can scan it for you if wanted, but as stated above this info is easily found online.

Edit, here is a link to a downloadable manual for the 4.3 including wiring diagrams >>> https://drive.google.com/file/d/1l0fOeDisw-Ot78kypOLYe_y3n_wXKMQX/view

 

[Scott Danforth]

Confused about the layout of my 4.3 mercruiser in my 1990 larson. Went to change out my exhaust risers and noticed on the back of the engine was a coil. My engine has an hei distributor so the coil, as it seems to me would be pointless. There are a few loose wires behind the engine that have eyelets on them so I would guess they were once attached to that seemingly pointless coil, but unfortunately I have been unsuccessful at locating a good wiring diagram for this engine/ boat. Even on iboats the ones that have been posted previously either don't open or don't show enough to check over everything. Does anyone have a complete schematic for a 1990 4.3 mer-cruiser with an alpha 1 outdrive. As a bonus would anyone have or know how to get a hold of a full boat diagram for this All American.
Thanks all. I look forward to your responses.

you are saying your motor has an HEI distributor with the coil in it? unless that distributor has a tag on it from DUI (davis unified ignition), and a tag that says SAE J1171. stop using it. someone swapped in a different distributor.

if you have a vacuum canister on the distributor it is an automotive distributor. if that is the case. immediately buy the right distributor. do not use the boat at all. running an automotive distributor in a boat is like buying a case of dynamite and holding lit sparklers. all you need is a slight fuel leak to meet Jesus.

Boats never came with an HEI distributor. they only came with ignition systems that have a separate coil.

wiring diagrams are in the factory service manual.

however standard wiring goes by color. grey wire is the tach, black is the ground and purple is the ignition.

original distributor from mercruiser would have been a Thunderbolt ignition (much better than any GM HEI) and it would have had a separate amplifier assembly from the distributor and trigger.

 

[Meames1]

"unless that distributor has a tag on it from DUI (davis unified ignition), and a tag that says SAE J1171. stop using it.

if you have a vacuum canister on the distributor it is an automotive distributor. if that is the case. immediately buy the right distributor. do not use the boat at all. running an automotive distributor in a boat is like buying a case of dynamite and holding lit sparklers. all you need is a slight fuel leak to meet Jesus."

Good info, I did not know why it was unwise to use a car-type distributor. I had "assumed" it was due to the wrong mechanical advance curve....but yeah, now it makes sense.

 

[jbcurt00]

Moved to the Mercruiser forum

 

[Rick Stephens]

The HEI is not going to have the right advance curve for a boat and besides, is not safe in a boat. Taking this to the next step, also need to look and see how the shift interrupt switch was wired to the HEI. May be some of that extra wiring and the shift interrupt got deleted. That wouldn't be good as the Alpha drive needs the shift interrupt to come out of gear.

It is not financially reasonable to purchase Thunderbolt IV ignition parts. Way too expensive these days. I have a '91 V6 that I installed from ground up in my boat and when I had a bad component in my Thunderbolt IV system I didn't hesitate for a second but went out and bought the excellent Delco Voyager ignition system. The timing curve is designed for a boat and works perfectly.

Everyone here is happy to help you with wiring issues as the system is simple and usually easy to describe or show schematics to get you up and running.

Rick

 

[Rslavinjr]

Wow, thank you all so much for the invaluable information. I had no idea it was so unsafe. I will definitely be looking further into what exactly is going on and will take pictures as soon as the weather permits. Its been pouring here all day and have the boat under a tight cover. At the moment since I have the engine cover and rear flip up cover removed to gain better access to the engine. It did strike me as odd that it had an hei in it since I've never seen a boat with one. Supposed to have a sunny day tomorrow so I'll get some good photos of the engine, loose wiring and distributor.

 

[Rslavinjr]

So after looking at the distributor it is most definitely a automobile distributor and not one made for a boat. The device that mounts to the port exhaust riser is still in place and in relatively nice shape. The coil looks like crap but could function just fine. I will have to see about a test procedure or just replace it with a better one since I have to replace the distributor anyways. I have located a couple of the thunderbolt 4 distributors for <$75. There is a loose wire that is white with a green stripe that im not sure where it connects to.

 

[Rick Stephens]

This might help. #10 is the shift interrupt switch.

 

[Rslavinjr]

And one of the engine cover with all numbers on it.

 

[Rslavinjr]

This might help. #10 is the shift interrupt switch.

Thank you for the diagram Rick. Where would that shift interrupt switch be located?

 

[Rick Stephens]

Where the shift cables are attached at the motor. Here's average picture, the Y shaped lever presses on the switch when shifting out of gear, in the water, cutting out the ignition for a revolution of the motor or two and unloading the dogs in the gearbox.

 

[Rick Stephens]

Before you go to work on it, read this page so you understand how the shift interrupt works. It will greatly simplify your rewire.

HOW TO: How the Shift Interrupt system works

Usually in the spring and summer we get a lot of posts regarding the shift system for the MC-1 (falsely referred to as Pre-alpha drives) to the Alpha 1 drives. There are a lot of wrong ideas on how and why the system works and why it's there to begin with. Maybe this will help explain how it...

forums.iboats.com

 

[Rslavinjr]

Thank you Rick for posting that explanation. I have those parts on my starboard riser so I'll be curious as to see how the previous owner wired it up. After reading how the shift interrupt works it explains why my buddies Searay would run great in the driveway and die when he tried to take it out on the water.