7.4 Bravo One...Need Thunderbolt IV Ignition Brainstorming

[bparsel]

1995 7.4 Mercruiser Bravo One with Thunderbolt IV Ignition.


Last Summer it started having issues, when hitting trim button the engine would cut out for a moment if running about 3/4 throttle. In August I hit the trim button, engine backfired, died, and did not restart. I winterized it and stored it for the winter.

Last week I installed a new coil, ignition sensor, and cap and rotor. The boat fired immediately and was starting better than it ever has. The engine wasnt flowing water though so this weekend I installed a new impeller.

After installing the new impeller, the boat started hard like it used to (pre new ignition components). I shut it down and then it wouldnt re-start.......NO SPARK...AGAIN!!! I have 12v's at the coil, I have 11.65volts on the red/white Ignition sensor wire.

I have even tried hotwiring both the kill switch and the neutral safety switch with no change. All other power and grounds look good.

I need some outside of the box thinking as I'm about to burn the boat to the ground.


Any thoughts?

 

[Bt Doctur]

disconnect the grey tach wire at the coil

 

[bparsel]

disconnect the grey tach wire at the coil

I'll give it a shot. I'm literally going to try every suggestion given. I just dont understand how after changing everything it started great...and then a week later spark is gone again.

 

[Bt Doctur]

a tach going bad even though its still giving you a reading can kill the spark On the TB-IV the module is held in place by the 2 bolts that protrude from the housing. Sometimes corrosion builds up on the contacts at the module. Dist removal and module removal and cleaning of the contact surfaces works.

 

[Bt Doctur]

Not your dist but the system is the same 4B-6 and 4B-7 in here. http://www.boatfix.com/merc/Servmanl/18/18B4R2.PDF

 

[bparsel]

When you say module are you talking about an Ignition Amplifier or the Ignition Sensor/Module inside the cap? I replaced the sensor inside the cap.

I appreciate your help.

 

[Bt Doctur]

http://www.boatfix.com/merc/Bullet/83/83_24.pdf

 

[Bt Doctur]

the one in the dist cap.

 

[bparsel]

the one in the dist cap.

Thanks, that sensor is brand new and the boat was starting perfectly? Ive run the tests and everything keeps pointing to the sensor again.....not sure how it could go bad with approx 3 minutes of run time?? The ignition amplifier keeps coming up in my research as well.


I havent been able to do the spark gap test on the white/green wire yet though. I'm going to pick a gap tester up this afternoon.

 

[Bt Doctur]

remove the tach wire from the coil before doing any testing you only want the grey wire from the amplifier connected to the coil. The grey wire in the engine harness disconnected

 

[bparsel]

remove the tach wire from the coil before doing any testing you only want the grey wire from the amplifier connected to the coil. The grey wire in the engine harness disconnected

Will do, thanks. I'll try this as soon as I get home this evening.

 

[achris]

Once that grey tacho feed wire is off, check the voltage on the white/green. It should swing between 0 and about 4.8v with the rotor window open and closed.

Chris....

 

[bparsel]

Once that grey tacho feed wire is off, check the voltage on the white/green. It should swing between 0 and about 4.8v with the rotor window open and closed.

Chris....

I'll double check that, although I dont think Im getting any voltage on the Green/White.


I pulled the tach wire last night....no change. I then hooked up a Spark tester off the coil wire and struck the Grn/Wht against ground and got no spark. I repeated this with my other coil I had per the manual...again....no spark.

This all points to the Ignition Amplifier per the manual. I just dont understand how the boat started and ran great last weekend with new ignition components and then back to nothing, doesnt seem like the amplifier would be the root cause.

 

[Bt Doctur]

would you like a amp to test with
Promise to send it back!

What voltage is the alt puting out?
Is there a ground wire pigtail from the module not grounded?

 

[bparsel]

would you like a amp to test with
Promise to send it back!

What voltage is the alt puting out?
Is there a ground wire pigtail from the module not grounded?

Kind offer on the Amp, and I may take you up on that. I might swing by Michigan Motorz this afternoon and see what they have laying around.

I havent found any grounds loose etc in my searching. I'm about at the end of my rope on this and just called the mechanics.....10 day turnaround right now but Im getting to the point of just writing a check and being done. Ive NEVER given up on any of my cars or boats before but this electrical is driving me nuts.

 

[bparsel]

I'm at the point where all of the reading I have done and testing etc continues to point to a new Amplifier...Ive found other threads with the exact same details as me that were solved with a new module. I'm debating cutting my losses on a $2-300 amplifier and just springing for a whole new system.


Any thoughts on going this route????

 

[Bt Doctur]

There are rumors that the large amplifier box was a Ford product. Could try looking at them, Never had a problem with conventional systems either.
Points are a possability

 

[Bondo]

Ayuh,..... The Delco Voyager is a common answer for those facein' yer dilemma,....

It's 'bout the same money for a full ignition system,.....

 

[bparsel]

Ayuh,..... The Delco Voyager is a common answer for those facein' yer dilemma,....

It's 'bout the same money for a full ignition system,.....

Youre referring to this setup?

These systems are effectively plug and play right? Take out Thunderbolt system, put in Delco or the one I listed above...make sure timing is correct and done right?

 

[achris]

Youre referring to this setup?

These systems are effectively plug and play right? Take out Thunderbolt system, put in Delco or the one I listed above...make sure timing is correct and done right?

As much as those selling this system would have you believe, no it's not 'plug and play'. There are a few wiring mods to make, and unless you know what you are doing and understand how both the system you're removing and the system you're replacing it with work, messing it up is very easy.

Chris......