Ignition Module Bad

[Rstorrie]

Mercruiser Thunderbolt IV ignition system. Sometimes almost 13v on + side of the coil, sometimes 10.5v at the + side of the coil. When at 10.5v, no start. When at almost 13v, fires right up. New cap, rotor, coil, key switch and kill switch. If I take the purple wire off the + post that runs to the ignition amplifier, I get almost 13v. When I touch the purple amplifier wire back to the + post, drops to 10.5v and again no start (Note: This is intermittent and sometimes it actually still reads almost 13v and starts). There is nothing on and motor is not running, just key in run position. Every connect on key to the battery to the motor components and battery connections all cleaned. New battery too. Does it sound like the Thunderbolt IV ignition amplifier is bad and shorting or something? When it runs, runs like a champ. Thank you for any help you can provide.

 

[alldodge]

What motor and year is it?

I think you may have a bad connection issue from corrosion or loose
Pull the 10 pin connector off and check the pins
When replacing key and kill, were the connectors in good clean shape?

 

[Rstorrie]

Replaced and cleaned everything, key, kill, coil, etc. Plug connector is clean and tight. No voltage change when wiggled. Ran another + wire from the battery straight to the key switch, no change in voltage to coil.

Constant 12+ Volts at coil usually, When it is acting up and volts drop to 10.5 and no start, I get spark at either the - or + post of the coil when I remove and touch either the the purple + wire or the grey - wire from the ignition amplifier to their respective posts on the coil. When the system is sending the correct 12+ volts at the coil, there is no spark when I touch either wire to the coil posts. Only sparks when low voltage drop.

 

[Rstorrie]

Wish there was a better thunderbolt IV troubleshooting chart. It gives a 0 and 12v flow, not a in between or partial volt flow, so the chart is worthless for me.

 

[Rstorrie]

It has to be the ignition amplifier. Isolated it down to the distributor sensor or ignition amplifier. Cleaned and tested the wires on the distributor that run to the ignition amplifier from the sensor, worked and passes the testing by grounding the wht/grn wire, volts drop to about 7, then returns to 12v. So must be the amplifier. After hooking the wht/grn wire back up to the distibutor and checking the coil voltage, it had dropped to 10.5v again. The weird part is, every time I touched the + side of the coil with the + probe, I could hear the spark fire inside the distributor when reading 10,5v. The meter probe does not add any voltage to the system, so I do not understand how it could make it fire. After a couple low volt sparks, it went back to 12v and the sparking stopped as usual and now reading 12v at the coil.

 

[alldodge]

Think a voltage like water in a hose, if there are no restrictions then everything has the same flow. Only way to get less flow is to have a restriction. You can squeeze the hose in the middle and everything before the squeeze point has full flow, everything after has less.

So if your seeing less the battery voltage on the coil, then there is a restriction somewhere before the coil

 

[achris]

Wish there was a better thunderbolt IV troubleshooting chart. It gives a 0 and 12v flow, not a in between or partial volt flow, so the chart is worthless for me.

Voltage doesn't flow, current flows. Voltage just has a 'presence'....

 

[Rstorrie]

It is not before the coil. I get constant 12.5 v all the time at the coil with one of the amplifier wires removed from the coil. When the ignition sensor or amplifier is acting up it drops to 10.5v and there is a spark inside the distributor from the sensor when the amplifier wire is touched to the + post of the coil key in run. Take it off again and back to 12.5v, then it stops and stays at 12.5v whether connected or not and runs, until the next time it acts up. When it is connected and 12.5v, it starts and no sparking inside the distributor before starting it.

 

[Toreh]

I also have this problem,13v in to the ignition module-beetween the grey and black wire in the plug,when i am measuring the voltage at the hvite/red from the ignition module i only get 11.5v,when i crank,it drops to 8-9v,i tried the ignition module in a similar boat/engine and i got the same problems.Are the voltage out from the ignition module to low?

 

[Toreh]

Btw i have change the coil and the distributor sensor,still the same

 

[alldodge]

I'm at a loss because of having trouble following.

I would say if the TBV (same but better for TB-IV) does not show what the problem is, then need someone smarter then me, which isn't hard to find

 

[Rstorrie]

Same boat as me. 10.5v at coil. Yesterday disconnected the distributor sensor from the system so the distributor had no connections whatsoever thinking it was the sensor and just left the amplifier connected. Still 10.5v, so not the sensor. Disconnected the only connection at the coil and that was the amplifier. as soon as I took the wire off the coil terminal to the amplifier, went back to 12.5v, touched it to the post again, dropped back to 10.5v. Must be a short in it. I will know more later this week, found a amplifier on eBay that works. See what happens when I connect this one up. If still doing it, ripping the TB IV system off and getting an aftermarket ignition system.