No Spark

[FreeBeeTony]

Went down to the boat tonight and would not start.
Was fine last time out last week.
​Determined no spark out of coil, confirmed 12v at + side of coil.
Need to complete troubleshooting sequence in manual.
​Would like to view a schematic while troubleshooting.
Do not see a schematic in the manual.
Can someone point me to a schematic of the TB-IV ignition system?

Thanks!

 

[Chaser 32]

No Title

Image found here http://www.marinemechanic.com/site/page250.html

 

[Chaser 32]

No Title

 

[achris]

...Can someone point me to a schematic of the TB-IV ignition system?

I can do you one better than that.... Here's a full description of how the system works, and how to troubleshoot it...

http://forums.iboats.com/forum/engi...-mercruiser-thunderbolt-ignition-systems-work

Chris........

 

[FreeBeeTony]

Thanks....now I can continue tomorrow night!!

 

[FreeBeeTony]

OK......according to the procedure, I have a bad ignition sensor.
​Removed the wht/grn wire from the sensor, installed a sparkplug on the coil wire, shorted the wht/grn wire to gnd and got spark!

Do these sensors go bad out of the blue?
​Is there a test to test the sensor individually?

 

[achris]

OK......according to the procedure, I have a bad ignition sensor.
​Removed the wht/grn wire from the sensor, installed a sparkplug on the coil wire, shorted the wht/grn wire to gnd and got spark!

Do these sensors go bad out of the blue?
​Is there a test to test the sensor individually?

Check your shift interrupt switch.

To test the sensor, arm yourself with a thin blade, like a steel 6" ruler. Check with a multimeter (on the volts scale) between the White/red and ground and ensure you have 12 volts. Then connect the meter to the white/green. Take the dissy cap off and turn the engine so the sensor is not 'covered' by the rotor windows. Pass the end of the ruler across the sensor face and watch the voltmeter. It should swing between 5 volts (about) and 0 volts (about)....

1. If you have no 12 volts at the white/red, dead module.
2. 12 volts at the white/red but no change at the white/green, dead sensor.

Do the sensors fail 'out of the blue'? yes. Electronics is a bit that way.

Chris...........

 

[FreeBeeTony]

EXCELLENT!!
That's what I was looking for!

Guess the sensor must need a good ground...........

I Have the old style w/ the studs, I see it was replaced by a newer one w/ a pigtail.
If I can find a "new" old style any reason not to use it? Would be easier to install.

 

[achris]

I would suggest you use the new style. They superseded them for a reason... Did you read up in my blurb about the differences between the sensors?

The difference in installation is about 3 minutes. But the new ones are a lot less prone to corrosion and bad grounds.

Chris......

 

[FreeBeeTony]

Yes I read it........I will go w/ the new one.

Thanks again!

 

[FreeBeeTony]

Any thoughts on using a Sierra part?

 

[achris]

Any thoughts on using a Sierra part?

I'm not keen one them.

 

[FreeBeeTony]

Did a little more testing...........
​Removed grn/wht wire from the dist and had ~ 4V on the wire.
​Re-installed the wire and had ~0.0V 0n the wire.
​Determined the impedance of post on the sensor to gnd was ~ 12 ohms when 12v was on the other post.
Still sounds like a bad sensor.........just a different mode of failure.

 

[FreeBeeTony]

Replaced sensor...........no change!!
Need to go back to square one........

 

[achris]

Module. You did have the shift interrupt switch and the tacho wire removed, yes?

 

[FreeBeeTony]

Shift interrupt but not tacho....
Will disconnect tacho wire tomorrow........!!!!

 

[FreeBeeTony]

Shift interrupt but not tacho....
Will disconnect tacho wire tomorrow........!!!!

 

[FreeBeeTony]

Noticed something else yesterday, tach did not show a reading when cranking the engine.
Not sure if it was before. Will verify a little later.

 

[FreeBeeTony]

OK.........still not working.
I found some old known good parts from a past troubleshooting experience.
I replaced the module....NG.
I replaced the coil.........NG.
I replaced the sensor.......NG.


Any other ideas?

 

[achris]

I'll say you have a wiring problem. Start checking voltages and connections.