No spark 1990 mercruiser 4.3l

[Chase25]

Good day folks , I believe I’m in need of replacing the thunderbolt 1V ignition module on my 1990 4.3l mercruiser . I had left the key on for about an hour with the boat not running and this cause my ignition module to heat up to the point it burnt and blistered my skin when I touched it . Now I have no spark . I tried replacing the coil but still have no spark . Should I be looking for something else or trying to find a replacement ignition module ? Also this module seems to be discontinued , is there a new boat safe ignition system I can put in instead ? Thanks !!

 

[achris]

Many replace the TB-IV with a Voyager HEI system. Personally I don't like that system, or option. The sellers of the Voyager systems will tell you it's a 'drop-in' replacement. It's not! You need to modify some of the engine wiring to get it to work properly with a shift interrupt switch. The TB-IV system is about the most reliable marine ignition system available. If I had a TB-IV system that needed a new module, I would look for a second hand module (plenty available on ebay, search '15247A1' or click HERE), or bite the bullet and buy a new TB-V replacement from Merc. Yes, it's a pricey unit, but I believe it's worth the extra couple of hundred.

I would run through the Thunderbolt troubleshooting flowchart before jumping to conclusions though.

Flowchart at the end of this document...
Thunderbolt Ignition systems

The replacement for your TB-IV module is -15247T02

Chris.....

 

[wshekar]

I purchased a used module from ebay about 4 years ago. Still going strong at a fraction of the replacement price.

I assume it is probably hit or miss with ebay though.

 

[Chase25]

Thanks for the help chris , I did most

Many replace the TB-IV with a Voyager HEI system. Personally I don't like that system, or option. The sellers of the Voyager systems will tell you it's a 'drop-in' replacement. It's not! You need to modify some of the engine wiring to get it to work properly with a shift interrupt switch. The TB-IV system is about the most reliable marine ignition system available. If I had a TB-IV system that needed a new module, I would look for a second hand module (plenty available on ebay, search '15247A1' or click HERE), or bite the bullet and buy a new TB-V replacement from Merc. Yes, it's a pricey unit, but I believe it's worth the extra couple of hundred.

I would run through the Thunderbolt troubleshooting flowchart before jumping to conclusions though.

Flowchart at the end of this document...
Thunderbolt Ignition systems

The replacement for your TB-IV module is -15247T02

Chris.....

so the green/white wire test is confusing me . I was unaware of that one however ei will do my best to try that tomorrow . The red/ white wire has 10.5 volts coming from the module to the distributor I unhooked at the distributor and tested with a multi meter . I assumed the lower voltage meant screwed ignition module or is that incorrect . Also the purple wire from the key to the system is proving 12.6 volts

 

[achris]

White/green wire test...

What I do is get an old spark plug, pull the centre HT lead out of the distributor cap and put the plug in that. Play the plug on the engine block (ground) so the gap is easy to see, and try to do it in a low light situation (as the sun is setting, or before it's rising, or in a shed/garage you can closed doors on). Remove the white/green wire from the distributor sensor (so it is still running to the module), and tap it against the engine block (ground) as quickly as you can. You should see a spark. If you see no spark, it's likely the module (or the coil you have already replaced. ).

Chris......

 

[Chase25]

White/green wire test...

What I do is get an old spark plug, pull the centre HT lead out of the distributor cap and put the plug in that. Play the plug on the engine block (ground) so the gap is easy to see, and try to do it in a low light situation (as the sun is setting, or before it's rising, or in a shed/garage you can closed doors on). Remove the white/green wire from the distributor sensor (so it is still running to the module), and tap it against the engine block (ground) as quickly as you can. You should see a spark. If you see no spark, it's likely the module (or the coil you have already replaced. ).

Chris......

Thanks so much ! And the red/white only having 10.5 v sounds ok ? Also I see you left me a pet number for the TB-5 if I did need a replacement . Do you happen to have a link to a site that still supplies them ? I found several today but everything said no longer available , perhaps that’s just from COVID haha