Re: IH 666 Weak Spark When Cranking

Posted by John T on September 11, 2016 at 12:09:14 from (216.249.81.101):

In Reply to: IH 666 Weak Spark When Cranking posted by in-too-deep on September 11, 2016 at 07:49:06:

First of all, in my opinion FWIW, IF IT EVEN HAS ONE ???? I just don't envision this as any "ballast by pass system failure" as discussed below. If it even has a ballast resistor ?? and a by pass when cranking arrangement ?? (aids in cold weather starting) often when those go bad such as the ballast becomes open, THEY WILL START AND PRODUCE FIRE WHEN CRANKING but die when you let off the starter. But you say yours "STARTS" when you let off the starter!!!!!!!!!!!!! which is the OPPOSITE of what happens if a ballast resistor is open on a tractor that uses a ballast by pass starting system.

EXPLANATION OF BALLAST BY PASS: Some 12 volt tractors use a 6 volt coil plus a series ballast resistor. If it has a ballast by pass to aid in cold weather starting, ONLY WHILE CRANKING is the ballast by passed so the coil sees full unballasted voltage. This may be like the "I" terminal on a solenoid or manual start switches with the extra small terminal. If the ballast became open she would fire as long as the start switch is depressed BUT DIE WHEN YOU LET OFF THE STARTER. HOWEVER yours STARTS when you let off the starter.

HERES MY FIRST GUESS. If the starter motor is bad and/or the battery is weak, while cranking the voltage is too low to produce a good spark BUT AS SOON AS THE STARTER IS OUT OF THE CIRCUIT AND BATERY VOLTAGE ISNT REDUCED, SHE CAN FIRE STRONG AND SHE STARTS.

Soooooooo instead of a bad ballast by pass system as discussed below, Ima thinking your battery is weak or you have a bad connection or the starter is drawing excess current thereby dropping voltage.

FIRST THING I would do is remove, clean and wire brush and re attach each and every battery and starter and switch and ground and cable connection,,,,,,,,,,,,,,,SECOND insure battery is good and full charged, a battery shop will load test it for free HAVE THAT DONE.......THIRD measure battery voltage while cranking, if it stays say 11 to 12 or so while cranking the battery is likely okay and the starter IS NOT drawing excess current HOWEVER if voltage drops way down say less then 10.5 the battery may be weak (load test will show) OR the starter may be bad and drawing too much current and dropping voltage causing a weak spark when cranking.

SECOND GUESS: You could have a faulty resistive ignition switch that's dropping voltage so when cranking the spark is too weak but even with the bad switch when the starter isn't drawing current and dropping voltage she can run when you let off the switch..........TO TEST FOR THAT see what the voltage is on the coils input (from switch) with ignition on and points closed??????????? It should be near the same as the battery voltage, if its way less, the ignition switch may have burned loose resistive contacts dropping voltage causing a weaker spark. TO TROUBLESHOOT run a hot wire direct from battery to coil to by pass the switch and hot wire the ignition coil, if it starts and runs fine hot wired but NOT using the ignition switch, the switch may be bad and resistive..........

I just think its either a weak battery or a bad connection or a bad starter or bad ignition switch instead of a bad ballast by pass system!!!!!!!!!!!!!!!! CHECK BATTERY VOLTAGE WHILE CRANKING (for bad battery or bad starter) AND CHECK COIL INPUT VOLTAGE WITH IGNITION ON AND POINTS CLOSED (for bad ignition switch, try to hot wire it)

John T

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