4.3 thunderbolt IV no spark

H

helicoprion

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Aug 20, 2009
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My name is mike and I'm a first time poster here.

I have a 1990 4.3 mercruiser with thunderbolt iv ignition and I am getting zero spark. I have gone through the whole thunderbolt flow chart. I have 12v at the coil, 12v at the white/red lead, and no spark when striking the white/green lead against a ground. The coil and ignition sensor are new. I have tried disconnecting the tach and the Shift interrupt switch.

The flow chart leads to a bad module but I have read a lot of posts here where the module was replaced and the problem was still something else.

I aquired the boat without hearing it run and the cover is off that covers the wires for the fuse/gauge panel leading me to believe the owner was messing with something in there.

I have read about a safety lanyard and kill swith but I'm not sure where these are located and have not checked them.

If anybody has any ideas that I could try before spending the money on a module I would much appreciate it.

Thanks!

Mike
 
achris

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Re: 4.3 thunderbolt IV no spark

If you have +12v on the coil, then the problem is not the lanyard... The next thing I would check is the grounding... Make sure you have a ground wire from the engine block to the distributor body. I had that problem years ago on my previous engine (1994 4.3LX). If you have followed the chart (with a new coil and sensor) and it says to replace the module, I'd replace the module....

Good luck,

Chris.......
 
H

helicoprion

Cadet
Joined
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Messages
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Re: 4.3 thunderbolt IV no spark

I checked for the ground and found it was disconnected from the distributor. I connected it and still no spark. It is grounded to the riser along with the module and ignition sensor. Is that a good enough ground or does it actually need to be on the block?

And if the problem is the module is it possible to just switch to an msd box or something like that?

Thanks!

Mike
 
Don S

Don S

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Re: 4.3 thunderbolt IV no spark

TB4troubleshooting.png
 
H

helicoprion

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Messages
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Re: 4.3 thunderbolt IV no spark

I have gone through that flow chart quite a few times

Thanks though!

Mike
 
achris

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Re: 4.3 thunderbolt IV no spark

For testing purposes, yes, but the advance curves are very different.... And the V8 module will think the engine turning slower than it really is (less pulses per revolution)....

Chris.........
 
H

helicoprion

Cadet
Joined
Aug 20, 2009
Messages
8
Re: 4.3 thunderbolt IV no spark

What's the best place to get one. They seem to be discontinued and all the ones i find seem to be for a V8.

Thanks for the help!

Mike
 
achris

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Re: 4.3 thunderbolt IV no spark

They are listed as NLA ex Merc... I looked up www.mercruiserparts.com and they list them as 'we have a few on the shelf', but they are costy little devils... $348 :eek::eek:

Part number you're looking for is -15247A1

Chris...........
 
H

helicoprion

Cadet
Joined
Aug 20, 2009
Messages
8
Re: 4.3 thunderbolt IV no spark

Wow! Looks like I won't be getting out this season.

Looking at some used ones I've noticed there are 2 different styles. The old models seem to not have a Plug in harness. Can they still be spliced in or are they completely different?
 
achris

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Re: 4.3 thunderbolt IV no spark

If it comes with the harness, grab it!
 
D

darrincates

Recruit
Joined
Jul 31, 2010
Messages
4
Re: 4.3 thunderbolt IV no spark

I just went through this exact same problem no spark, followed the exact same flow chart, which led to replace ignition but it wasn't ignition .... It was $80 Crank sensor under distributor in the cup that the rotor sticks up out of ...
 
Bt Doctur

Bt Doctur

Supreme Mariner
Joined
Aug 29, 2004
Messages
19,348
Re: 4.3 thunderbolt IV no spark

Did the V6 ever have points? convert back.
 
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