Mercruiser 4.3 V6

[ChrisCraftJohnny]

I am new to iboats and I have to say that I've learned much from all the great topics on the site.

I have a 1988 21' Chris Craft Scorpion with a Mercruiser 4.3 V6 / Alpha one outdrive.

I will make the first question an easy one.

What was the original ignition coil installed in this engine?

Thunderbolt IV, with a Prestolite Distributor.

Previous owner installed a Accell Super Coil in it's place. I don't want a automotive coil on the boat. And want to get this set-up back to original.

I will have more questions soon.

Thanks a ton!

Johnny

 

[Don S]

Re: Mercruiser 4.3 V6

I'm not really sure what you are asking, but the distributor for Mercruiser in that era was a Thunderbolt distributor. NOT Prestolite.
If you have the OEM distributor, then just head off to your local Mercruiser dealer with your engine SN and get the right coil.
It should be PN 805570A2
If you want to order it, here is one place. Just type in the number above.

Now, if the previous owner replaced the distributor as well as the coil. Then you will need a lot more to get things back to normal.

If you go up to the Adults Only sticky at the top of this forum, you can download a manual with pictures and details of the system.

 

[ChrisCraftJohnny]

Re: Mercruiser 4.3 V6

Don,

I could be wrong about the distributor being a prestolite. All I know right now its that the distributor cap has a 4 screw design.

Thanks for the info.

 

[Don S]

Re: Mercruiser 4.3 V6

All I know right now its that the distributor cap has a 4 screw design.

That is the standard Mercruiser Thunderbolt distributor. Used for many, many years. Still in use.

 

[ChrisCraftJohnny]

Re: Mercruiser 4.3 V6

Don,

Thanks for the info. I am glad to know that this is the orginal distributor.
The previous owner had the engine rebuilt. The shop who rebuilt it did a good job. But the owner did a limited job on hooking up the ignition and also did not refresh/rebuild the 2BBL Mercarb when he had a new engine to do so on.

He had 4 of the 6 spark plug wires going to the wrong clyinders! The engine ran OK but never seemed 100% to me. What I found out was that the distributor was not installed correctly when put back into the engine. It was basically "thrown in" the engine and then compensated for by advancing the timing and moving the plug wires around until the engine ran OK. The old owner felt the numbers marked on the distributor were just for fun and don't matter!

I first ask my friend who is a 40 year certified GM mechanic if this could be possible. He told me yes and that he has seen this before when DIYers don't understand the importance of getting the distributor installed correctly.

Johnny

 

[Don S]

Re: Mercruiser 4.3 V6

Go look at the adults only sticky at the top of this forum. You may be surprised at all the good stuff you find.

 

[joncrisler]

Re: Mercruiser 4.3 V6

Both Accel and MSD made distributers suitable for marine use at one time. Before spending money on this I would check the part number. I put a MSD marine-rated coil on my 454 many years ago when the original coil went bad.

 

[ChrisCraftJohnny]

Re: Mercruiser 4.3 V6

Jon,

Thanks for the input. I know MSD and Accell make great products. And I know that the Super Stock coil on the engine works. I just want to go thru everything now that the season is over And replace with genuine Mercruiser parts. The coil is old, and with the bad work the previous owner did on the ignition system, I just want to replace most of the main ignition components so I can get this thing purring like it should and to not have to worry next season on the water.

Johnny

 

[ChrisCraftJohnny]

Re: Mercruiser 4.3 V6

Don,

Thanks again buddy for the "Adults Only" tip. I found the Mercruiser manual for my application and all I can say is OH YEAH!

The 4.3L V6 has an uneven mechanical firing sequence. The cam on the distributor is uneven. It has sharp lobes and round lobes. You MUST have a round lobe in sync with the #1 cylinder. I can bet that he has the thing a** backwards.

Will let you know what I find out on Friday.

Thanks a-million. Love this site!

 

[Don S]

Re: Mercruiser 4.3 V6

The Thunderbolt IV distributor is electronic and doesn't have a cam lobe like you are referring to. Those sharp and round lobes are only on points type ignition.

 

[Chris1956]

Re: Mercruiser 4.3 V6

Johnny, I had the exact motor for some years. I found that the distributor would only install into the block properly in two positions. These were 180* apart. Of course if you had it in wrong, the plug would fire on the exhaust stroke, instead of the compression stroke.

The distributor had a six-lobe reluctor and a sensor under the cap. All advance was electrical, no vacuum or mechanical.

 

[45Auto]

Re: Mercruiser 4.3 V6

The old owner felt the numbers marked on the distributor were just for fun and don't matter!

The old owner was right. They really don't matter. What determines the #1 position on the distributer cap is where the rotor is pointing when the #1 cylinder is at TDC. The numbers are handy for a reference if the distributor is installed in the factory orientation so that the rotor is pointing at #1 on the cap when #1 cylinder is at TDC. No reason not to do it that way, doesn't take but a couple of seconds to find the right tooth on the distributer gear.

But if the distributor is installed with #1 piston at TDC so that the rotor is pointing at #3 on the cap for example, then that #3 on the cap is really #1. If the wires are then installed in sequence according to the firing order the engine will never know the difference.

The engine ran OK but never seemed 100% to me.

What all this means is that if the old owner installed the distributer with the rotor pointing at the wrong pole on the cap, but then compensated for it by shifting the plug wires, it's going to make no difference in how your engine runs when you change it back so it lines up with the factory numbers.

 

[ChrisCraftJohnny]

Re: Mercruiser 4.3 V6

I understand what you said. I had hoped that the reverse install made a difference.

The problem still remains. I have rough idle with lots of black smoke out of the exaust and BLACK fouled plugs. Was thinking ignition when I saw the wrong placement of plug wires. But it may be the carb.

It has the 2bbl Mercarb with one mixture screw. During troubleshooting I turned the mixture screw in alll the way and the engine did not stall like it should. I believe that means that fuel is still entering the manifold via the carbs bowl. The float could be bad as well. When you have the ignition key on for a bit (say you were checking something else out on the boat) and druring that time, the fuel pump was running, and then you try to start the engine, it's in a flooded state and is very hard to start. I know the engine is running rich so this is where I should look next I believe. Carb Rebuild kit?

Any ideas?

Johnny

 

[Bondo]

Re: Mercruiser 4.3 V6

When you have the ignition key on for a bit (say you were checking something else out on the boat) and druring that time, the fuel pump was running, and then you try to start the engine, it's in a flooded state and is very hard to start. I know the engine is running rich so this is where I should look next I believe. Carb Rebuild kit?

Ayuh,... A rebuild kit, or replace the carb,...Yes...
Also,...
The fuelpump should NOT be running with the key On,+ the motor Off...
It should be wired thru an oil pressure switch down low on the portside of the block...

 

[ChrisCraftJohnny]

Re: Mercruiser 4.3 V6

Got my Quicksilver carb rebuild kit today. Only way to go on this item. Complete OEM kit, even came with a float measuring tool. $59.00 USD. I have read about all the problems others have had with aftermarket carb kits. So I went with the best.

Also, about the above topic. I still feel that installing the distributor the "wrong way" and then compensating for the mistake via moving wires around is the wrong way to go.

I also have a feeling that it can rob power and may cause some confusion between the moudle, coil etc. I will be installing the distributor correctly after I get the carb rebuilt.

Any thoughts on this matter?

Johnny

 

[ChrisCraftJohnny]

Re: Mercruiser 4.3 V6

Oh yeah, thanks for the help again Bond-O.

 

[Don S]

Re: Mercruiser 4.3 V6

Also, about the above topic. I still feel that installing the distributor the "wrong way" and then compensating for the mistake via moving wires around is the wrong way to go.

Read my reply above (#10)
There is not different lobes on your distributor. You have a Thunderbolt distributor. NO LOBES AT ALL.

 

[ChrisCraftJohnny]

Re: Mercruiser 4.3 V6

Don,

I understand I don't have the points type distributor.

But I still feel installing the thunderbolt 4 distributor so that the firing order does not jibe with the cap numbers is wrong. And can affect max power output of the engine.

Your thoughts?

Johnny

 

[Don S]

Re: Mercruiser 4.3 V6

But I still feel installing the thunderbolt 4 distributor so that the firing order does not jibe with the cap numbers is wrong. And can affect max power output of the engine.

Makes no difference on the TB distributor.