Ignition Modules

I was getting no spark from the spark plug ignition wire, so I went to my local small engine repair shop for a replacement ignition module for my old Briggs equipped Snapper mower

(12F802 2021E1 99062956)

The mechanic there suggested I check some other things first--- file/sand off the module where the body of the module makes a ground connection and check the switch for a good connection.


Anyone care to predict the odds that will solve the problem?

By the way --- there is a wire connection apparently to a switch on the safety shutoff to the mower. But how does that work? I would have thought that the body of the module provided the ground, so what is that connection doing?

 

If you disconnect the small black wire (the wire that goes to the switch) then test for spark. If no spark it can be safe to assume the coil is bad.
The ground wire should be "open" when the switch is in the run position. The "off" position should "close" this lead to ground which prevents the charge produced by the magnet and coil from reaching the high tension lead.
Not sure that is a direct answer but hope it helps.

 

Ahhh.

I'm supposing then that there are two coils --- a low voltage coil that develops voltage/current from the magnet and a secondary coil that ups that initial voltage to high voltage for the spark plug?

That lead from the ignition coil grounds out that primary voltage?

And if the switch doesn't open properly, the voltage remains grounded out so no high voltage can develop even though the ignition module is OK?


I polished every point of contact on the ignition module with a wire brush and sandpaper, did the same to the screws and connections for the module on the mower and polished up and operated the switch connections and checked to see that they seemed to open and close properly with the limit of travel provided by the mower deadman lever.

When I reassembled everything, it fired up and operated several time just fine.

However, it did that once before and then quit again, so I figure I will need some experience with it to determine if the problem has been repaired.

In my furnace repair trade, I often found that erratic operation often indicated a bad electrical connection someplace. That might have applied in this problem as well.

Thank you for your comments, Fixit!

 

Some coils do show signs of failure at operating temps. Once they get heated resistance can increase to the point of failure. Usually these will fail all together, eventually, but you can test as I mentioned above at the moment of failure and if no spark until it cools, then that would be a good indication of coil failure.