Ignition theory of operation

[84btracker]

I have a 1984 75hp 4clyn. Mercury. Can anyone explain the theory of operation in the ignition? Im not getting fire / voltage to the plugs, or coils for that matter, I do have the proper 180 and 20 V from the stator but that?s it. I?m lost after that. How does the trigger work? How does and what does the switch box do or work?

 

[Yepblaze]

Re: Ignition theory of operation

Do the required ignition system diagnostic testing procedure with the correct tools, per the manual's procedure and replace components as required.

I have yet see anyone work around it with much sucess.

 

[Laddies]

Re: Ignition theory of operation

The trigger is 2 separate windings that fire of the N/N and S/S ends of the magnet that is the center hub of the flywheel and each winding controls 2 cyls. so you normally will lose 2 cyls at a time from failure. the trigger advances and retard the timing by moving back and forth. The box receivers the voltage generated by the high and low speed stator windings runs it through a capacitor and wait for a impulse from one of the trigger windings to tell it when to fire the right coil, the box contains SCR switches a bias and capacitor among other things. Would you like a build sheet for the system?

 

[84btracker]

Re: Ignition theory of operation

Yes a build sheet build sheet would be great thank you

 

[Laddies]

Re: Ignition theory of operation

Each trigger winding should test 4+volts

 

[84btracker]

Re: Ignition theory of operation

Im not getting 4v from the trigger of either side i get the right ohms but I only get 1.2-1.6 volts AC from the tigger guess that would be it...........right.

 

[Laddies]

Re: Ignition theory of operation

Although it could be the trigger I would think it highly unlikely that both windings quit at the same time. Having the advantage of having parts I think I would lean toward a shorted rectifier in the box and try a box first, I know that is not possible for the owners to do and wish I could come up with a better answer. Have you tried to check for voltage with the wires disconnected just to see if it increases, I would think that a large increase in voltage would increase the possibility on a short.

 

[j_martin]

Re: Ignition theory of operation

Although it could be the trigger I would think it highly unlikely that both windings quit at the same time. Having the advantage of having parts I think I would lean toward a shorted rectifier in the box and try a box first, I know that is not possible for the owners to do and wish I could come up with a better answer. Have you tried to check for voltage with the wires disconnected just to see if it increases, I would think that a large increase in voltage would increase the possibility on a short.

In the switchbox.

hope it helps
John

 

[84btracker]

Re: Ignition theory of operation

I took all my readings from just leads (disconnected from the switch box)

183-185V from the low speed side of the stator 21-23V from the high speed side of the stator.

854OHMS from BLK and BRN leads from the trigger

854OHMS from VOI and WHT leads from the tigger

1.9V from BLK and BRN from trigger
1.9V from VIO and WHT from trigger

 

[84btracker]

Re: Ignition theory of operation

Yeah turns out laddies was right. It wasn't the trigger, still no voltage. This leads me to believe its the rectifier. Any suggestions on how to test the rectifier?

 

[Laddies]

Re: Ignition theory of operation

I also doubt the recifier but simply disconnect the 2 yellow wires from it and see if it has spark. There is no test for the one in the switchbox.

 

[84btracker]

Re: Ignition theory of operation

Ok, Ill try that tomorow. I Have honey do list for today. Laddies youve been a big help, thanks.