Thunderbolt iv coil voltage?

[bcons]

89 thunderbolt iv on a 305
I've been chasing ignition gremlins in this thing all summer.
When the engine is running at idle what should the voltage read when leads are on the pos & neg terminals of the coil?
Right now at idle the positive term with the engine block as a ground reads 12-13v
When reading pos term voltage and using the negative terminal as a ground it reads 2.2-2.3v
Is this correct?
Thanx

 

[Aloysius]

Re: Thunderbolt iv coil voltage?

Possibly. Remember it is the "make and break" of the NEGATIVE side of the coil that causes the spark. You are reading some internal resistance in the ignition unit, which may or may not be normal for your specific electronic ignition. I will say that when cranking, this reading should change (pulse) for each firing cycle.

 

[Don S]

Re: Thunderbolt iv coil voltage?

That is just a voltage drop test. No specs for it.
What kind of ignition gremlins are you having?

 

[bcons]

Re: Thunderbolt iv coil voltage?

Similar to lots of others.
Most of the time the boat runs great and as it should up to 2-2500rpms. Open it up and 2-45 mins (always different) later bogs & dies (it acts like out of gas, but it's not) Won't start again for 20-45 mins.
So I replaced cap, wires, module in distrib, coil. The only thing I didn't was the one mounted to the riser.
Recently a couple changes, the last time out I kept it under 2k ran fine, put in neutral to drift fish, but this time I left the motor running at idle 15 mins later it died (at idle & wouldn't restart) 20 mins later it was fine again. I can't duplicate the problem on muffs or at the dock. I've tried to meter everything following the flow chart, but no luck.

I just didn't know if that much of a voltage drop across the coil was normal.
The other question, is there a cutoff related to engine temp? Temp gauge has always been moody, and during this last problem at idle temp gauge quit completely.

 

[Don S]

Re: Thunderbolt iv coil voltage?

When the engine dies, have you checked to see if there is spark?

The other question, is there a cutoff related to engine temp? Temp gauge has always been moody, and during this last problem at idle temp gauge quit completely.

Nope, no temp cutoff.
From the sounds of things you have loose or corroded wires somewhere.

 

[bcons]

Re: Thunderbolt iv coil voltage?

Checked the 2 old school ways, 1st sprayed starting fluid into carb, nothing not even a burb. Then the nail in one plug wire holding next to ground nothing.

 

[Don S]

Re: Thunderbolt iv coil voltage?

What you are going to have to do is test it when it dies.

When it dies, do you have power to the + terminal of the coil with the ignition switch on?
Basically, you have to follow the flow chart when it doesn't run.

 

[Aloysius]

Re: Thunderbolt iv coil voltage?

There very well could be a connection between the ignition problem and the temp gauge problem. Both are powered through the ignition switch and go to ground at the engine. Both are voltage sensitive.