Thunderbolt IV spark loss

[Dazmatic]

Hi all, I’m new to the Forum and I’m from Perth, Western Australia. I found my way here because- you guessed it, I’ve got a problem I’m hoping someone that’s played around with them a lot more than I have can give some advice.

I have a skiboat with a MIE260 5.7 with TBIV ignition system. Intermittent no spark. It’s at about a 50/50 on any day of the week if it gives spark or not. I followed the troubleshooting guide, disconnected tach wire from coil, there’s 12v at coil + and going from the EST module into the distributor. Stricking out the white/ green wire to earth gives a spark EVERY time.

As per flow chart I fitted a new updated distributor pick-up sensor- fitted the new extra earth wire to bellhousing bolt where battery earth cable is fitted. While I was there I renewed the dizzy cap and rotor button (ok... I broke the original rotor prying it off) All earths have been cleaned and eventually I ran new earth wire from battery earth cable up to the EST module earth on the exhaust riser. She fired up and I thought we were ok. Not so.

Checked everything mentioned in the flow chart another 5 times and convinced myself the new distributor module was faulty (yeah I know... unlikely, but that’s where I found myself) Surprise surprise, still the same with a second new distributor sensor.

This is getting long now so I’ll try to get to the point. I borrowed a coil and dizzy, coil made no difference. Plugged in borrowed dizzy and spun it by hand- (motor had no spark for the previous 30 minutes) had spark now. Fitted donor dizzy- no spark again.

I’ve just discovered tonight by playing around, that by plugging in the dizzy out of the motor (with earth wire earthed) and spinning by hand fast we get good spark. Turning dizzy slowly, like cranking speed, gives no spark, or 1 spark every now and again. I’m thinking the EST module/amplifier on the exhaust riser is at fault. My problem is a replacement is $700+ Aussie dollars so I’m hoping for some thoughts on if that could be the culprit. It’s had a different coil, dizzy and the problem stayed, so not much left other than that. Oh, when spark is either good or bad, manipulating the wiring loom makes zero difference.

Any input will be appreciated

Regards- Darren

ps, I’m happy to stick with the Mercruiser way, I don’t mind keeping with TB ignition.

 

[alldodge]

Sure sounds like you have accomplished the testing procedure correct.
If there are no bad connections, and 12V stays on the Red/White wire and coil + terminal when the spark doesn't happen, then I would lean toward the Ignition Module.

The module is electronic and normally wouldn't work and then not work unless maybe a bad connection inside the unit. The TB modules can be found but it can take a lot of looking and then there is also a good possibility it can be bad.

If you do decide to replace I would go with the Delco EST

 

[Rick Stephens]

When I had a similar failure I did not go to the step of purchasing any T IV components but went straight to Delco Voyager EST. No longer worth it to keep going down that path.

 

[Scott06]

you may want to look on ebay for used modules. I bought two (one for a spare) for like $200 each

the only other thing i would think to verify is under load do you still have 12 v at the coil ? Do you have corrosion in the harness or at the cannon plug that your losing voltage under load like charging the coil

 

[Dazmatic]

you may want to look on ebay for used modules. I bought two (one for a spare) for like $200 each

the only other thing i would think to verify is under load do you still have 12 v at the coil ? Do you have corrosion in the harness or at the cannon plug that your losing voltage under load like charging the coil

I hooked up a relay to the coil + wire as part of my fault finding. It didn’t make any difference so I returned to factory. I’m very confident the 12v supply to the coil is stable, however now I know it’s at low distributor speed I might apply direct battery hot wire to the coil to see if there’s any change.

Thank you.

 

[Dazmatic]

Update. There are no mercruiser modules, or Delco Voyager kits in Australia. I’ve Ordered an Aeroflow HEI distributor to get me going again.

Thanks for the input.

-Darren.

 

[Rick Stephens]

I don't believe that Aeroflow makes a marine ignition system. You are asking to die and take anyone around with you using an automotive ignition,

 

[Dazmatic]

I don't believe that Aeroflow makes a marine ignition system. You are asking to die and take anyone around with you using an automotive ignition,

Hi mate, I heeded your advice and I did indeed go for a marine distributor. I went the MSD ready to run marine version, with adjustable mechanical advance and no vacuum advance. I gotta tell you that was the only marine distributor I could get here, and I had alot of trouble getting it. It cost a pretty penny too... I had to pay a decent “COVID Tax”

From speaking to a lot of people, and looking at a bunch of Australian ski boat photos, I can tell you there are heaps of people not running marine distributors down here.

Thanks for your advice.

 

[Rick Stephens]

Hi mate, I heeded your advice and I did indeed go for a marine distributor. I went the MSD ready to run marine version, with adjustable mechanical advance and no vacuum advance. I gotta tell you that was the only marine distributor I could get here, and I had alot of trouble getting it. It cost a pretty penny too... I had to pay a decent “COVID Tax”

From speaking to a lot of people, and looking at a bunch of Australian ski boat photos, I can tell you there are heaps of people not running marine distributors down here.

Thanks for your advice.

Worth it to take the risks seriously. Worldwide, most likely more boats are bombs than aren't. All you can do is take care of you and yours and keep them safe.

My best to you mate!

Rick