Re: Coil will not fire

Posted by John T on August 16, 2012 at 06:10:14 from (216.249.82.117):

In Reply to: Coil will not fire posted by FrankxR on August 15, 2012 at 19:05:18:

YOUR STATEMENT

"There is six volts on the -side of the coil and I am using a starter (hot wire) switch to ground the + coil primary. You can see on the tractor amp meter that there is good current draw on grounding the coil"

MY RESPONSE

If its a correct and working typical 6 volt coil Id expect a current draw of around 3 to 4 amps if 6 volts is applied across its terminals

YOUR STATEMENT

"On the HV side I have inserted a spark tester and attached this to a ground. Opening and closing the primary switch is not giving me a spark."

MY RESPONSE

If the coil is good and youre testing it by manually applying but then removing voltage across its terminals, each time the voltage is removed (like points opening) a HV spark out the top HV tower terminal (using a plug wire) should easily jump a 3/16 or so gap to frame ground. That will happen regardless if you have a condensor in the circuit or not, although the spark would be greater if one were used

YOUR STATEMENT

I have already replaced the ignition switch because it was displaying high resistance due to a low voltage on the battery side of the coil ( as low as 3.5 volts ) when grounded. Now when the coil is grounded the voltage stays around 6 volts. Am I testing this coil properly? Is it possible that the battery has too much resistance? I sort think not due to the size of the deflection on the amp meter.

MY RESPONSE

Again a typical working 6 volt coil LV primary would draw around 3 to 4 amps and thats NOT enough current draw to drop the battery voltage (IFFFFF its a good and charged battery) anything significant. A high currrent starter motor draw can reduce battery voltage, but a 4 amp draw should drop battery voltage unless the battery is bad assuming all else and wiring is okay

YOUR STATEMENT

The big difference between the old coil and the new coil is the primary resistance. The old was about 22 ohms and the new is about 1.7 ohms.

MY RESPONSE

A typical 6 volt coil would have a LV primary resistance of maybe 1.2 to 2 ohms certainly NOTTTTTTTTTTT 22 ohms

I suggest you run my Ignition Troubleshooting Procedure below for a systematic approach to determine the cause of no spark, but a coil LV primary of 22 ohms sounds baddddddddd and so often the cause of no fire is the points are bad or pitted or burned or not gapped right or not closing. Next problem may be a weak (causes weak spark) or shorted (causes her not to fire) condensor

Check the points, run my procedure is my advice, let us know what you find

http://www.ytmag.com/cgi-bin/viewit.cgi?bd=farmall&th=5745

John T

• John T's Ignition troubleshooting

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