Thunderbolt IV Question

[ChrisCraftJohnny]

Anyone know why the PO of my boat wired the Thunderbolt IV ignition amplifier directly to my Perko Bat. slector switch? He gave it a dirrect 12 volt source when the bats are turned ON.

The manual shows it wired different. (right way)

Anyone ever seen this? Is this a quick fix masking some wiring problem?

Thanks!

 

[Bondo]

Re: Thunderbolt IV Question

Nope,... Sounds like a Dumb Idea though....

You Are putting it back to Right, I hope...

 

[bomar76]

Re: Thunderbolt IV Question

Is this a quick fix masking some wiring problem?

Thanks!

Yes.

He has buggered up the wiring for whatever reason and used this method (which I fully endorse if engine won't run and you are 12 miles off shore and a typhoon is about to strike but for no other reason) as a very half azzed attempt to fix it.

 

[ChrisCraftJohnny]

Re: Thunderbolt IV Question

Thanks guys,

I knew it was not right just from the wire he used and from looking at the diagram from the Merc manual.

Yes Bono, I will fix it right!

This engine also has the electric fuel pump installed. I have read and been told on here that it should be wired to the oil pressure switch. Mine is not.

When the ignition key is turned to ON, the pump starts running. (Iknow this is wrong)

Which leads me to my next question. Is this electric pump OE? Or did a 1987 4.3L V6 have a mechanical pump. The pump being wired wrong points to the meachnical pump being OE.

Thanks!

 

[Bondo]

Re: Thunderbolt IV Question

Is this electric pump OE? Or did a 1987 4.3L V6 have a mechanical pump.

Ayuh,... If it was mechanical, it's probably still mounted on the foreward starboard corner of the block...

This engine also has the electric fuel pump installed. I have read and been told on here that it should be wired to the oil pressure switch.

Merc mounts that switch on the lower portside of the block, just ahead of the oil filter boss...

 

[bomar76]

Re: Thunderbolt IV Question

....and of course, either the electric or mechanical pump need to be marine rated.....

 

[Don S]

Re: Thunderbolt IV Question

Merc didn't start using the electric fuel pump until 92. So you should have a mechanical pump.

 

[ChrisCraftJohnny]

Re: Thunderbolt IV Question

Thanks Don,

What about this now?

Say I install a marine approved mechanical fuel pump. This Boat is has a
RACOR water/fuel seperator in addition to the Quicksilver mounted on-engine water/fuel filter.

Can a mechanical pump draw through those 2 units OK and still deliver the 5 PSI to the carb?

OR, is this the reason the PO switched to a electric pump? Not sure if the RACOR system is factory.

Still trying to un-do all the PO's DOING!

Thanks.

 

[Bondo]

Re: Thunderbolt IV Question

Ayuh,... from the closed thread...

2 filters ain't a Problem in itself,....
But I have no idea why you have 2,.. 1, kept Clean is more than sufficent...

My guess is, the block has been replaced with a newer 1, without a fuelpump boss....
And,..
All the work was done by a Real Hack...

 

[Don S]

Re: Thunderbolt IV Question

Either pump will pull through both filters. Really not necessary on Mercruiser due to the size of the engine filter. BUt they do need checked and replaced yearly to do their job properly. That means remove it and dump it out and see if there is water in it. If there is more than a couple spoon fulls of water, then you need to clean the tank. If no water, put on a new filter for the next year.

PS, the mechanical pumps are better. Less things to go wrong. In later models, there wasn't the option to use a mechanical pump, because the automotive side was all EFI and required electric pumps for control.

 

[ChrisCraftJohnny]

Re: Thunderbolt IV Question

Sorry about the confusion. I thought I was changing topics from Ignition to Fuel system. So I made a new post. I guess it's OK to allow the thread to morph into different topics. Cool.

Thanks.

This is the original engine. Just remanufatured. It was sent out and bored over .030 with all new internal parts.

I have had so much to do to it that I have not even looked to see if it has the block-off plate installed where the old Mech. pump lived. Last Mechanical pump change I did was 15 years ago in a snowbank on a Buick 3.8L LOL!

Thanks guys.

 

[Don S]

Re: Thunderbolt IV Question

Normally it's not a good idea to change, but this one changed early (post #4) to the fuel pump and away from ignition.

 

[ChrisCraftJohnny]

Re: Thunderbolt IV Question

Don, Bondo,

I looked up a Mech. Fuel Pump. It says it has a provision for venting to the carb. How should that be done?

Thanks!

 

[ChrisCraftJohnny]

Re: Thunderbolt IV Question

Wait! I just answered my own question.

I just got through rebuilding the 2BBL Mercarb. Came out nice!

I could not figure out what that little nipple on the air horn was for.

Now I expect I have guessed. That is where the vent line goes to the Mech fuel pump.

Am I correct?

Thanks.

 

[Bondo]

Re: Thunderbolt IV Question

Am I correct?

Ayuh,... The Answer to that question is hidden,...
Up in the Adults Only section at thetop of this forum are the Factory Manuals,...
The 1 for your motor, has that Answer....

There's Nothing Wrong with runnin' an electric fuel pump,... Just wire it Properly, that's all....

 

[ChrisCraftJohnny]

Re: Thunderbolt IV Question

I have the factory manuals. Used them to help me rebuild the carb.

But they don't show or mention that little right angled nipple on the air horn.

I would think from what I have learned about Marine Carbs, (that they vent into the carb instead of into the atmosphere) ala Automotive carbs.

That this nipple would be there for the Mech Fuel Pump's vent line so the pump can vent into the carb.

Yes? No?

Thanks!

 

[bomar76]

Re: Thunderbolt IV Question

When the diaphram in fuel pump ruptures the fuel will go into the carb instead of the bilge where an errant spark would ignite it and kill you.

Ruins your whole day on the boat when that happens.

 

[achris]

Re: Thunderbolt IV Question

When the diaphram in fuel pump ruptures the fuel will go into the carb instead of the bilge where an errant spark would ignite it and kill you.

Ruins your whole day on the boat when that happens.

Close, and with a similar result, but the fuel will go into the sump, not the bilge. If there is a spark or source of ignition the engine explodes internally, turning your boat into Apollo 21.... and you into shredded jerky...

Chris......