Super c no spark

[theog9n]

hello,
i am working on my father in laws tractor, it is a 12v conversion that ran when parked...lol! We have replaced the wiring harness, new coil, distributor cap, plugs, wires, points and condenser. Here is were i am at....I get 12v to the positive side of the coil. On the negative side i get 12v when the points are open and 0v when points are closed. While turning over the highest voltage is 3.6 on the neg side of the coil. All that to still get no spark to the plugs????


thank you in advance for any help!
Matt

 

[John T]

This part sounds right

.I get 12v to the positive side of the coil. On the negative side i get 12v when the points are open and 0v when points are closed

This part doesnt sound quite right HOWEVER it depends on the cranking speed PLUS the type of meter and response and its damping.

While turning over the highest voltage is 3.6 on the neg side of the coil

Have you worked through my Troubleshooting Procedure??

John T
John Ts Ignition Troubleshooting

 

[used red MN]

If you are using a cheap digital meter on the distributor side of the coil while cranking I am going to say the meter is just not giving you a true reading. An analog meter with a needle would probably give a voltage reading closer to what John T would expect to see. I am sure it is in John Ts steps but next I would go to pulling the high tension wire from the coil out of the distributor cap and hold it an 1/8 to 3/16 inch from the block and see if you have spark while cranking. If you do how does the inside of the cap look corroded terminals or moisture?

 

[Mrfred54]

You haven't mentioned rotor???

 

[Ky Cub]

If it has an external resistor, that could be bad.

 

[Janicholson]

Assuming the alternator is a standard negative ground type, the coil should be attached with the negative terminal of the coil hooked to the distributor. If this is the case, the negative side should flash voltage on-off-on-off as the starter turns the engine. Voltage on the ignition switch side of the coil should stay up close to 10.5 to 11 volts while cranking. If the coil is the original coil it needs a ballast resistor between the ign. switch and the coil (the original coil has an ohm reading of 1.2 to 1.5 Ohms. a true 12v coil will be about 3 ohms. A true 12v coil does not need a resistor. Jim

 

[theog9n]

We did put a new rotor on and the new coil has an internal resistor.
Was using a digital fluke meter.

I think I'll try the suggestion of pulling the main coil wire to see if there is spark there. If so the the problem must be in the cap/rotor area, correct?

 

[gene bender]

clean the points they probably have a film on them takem to a wire wheel for best results

 

[rvirgil_KS]

We did put a new rotor on and the new coil has an internal resistor.

If it has a new coil with about 3 ohms resistance between + and - posts, AND it still has an extra resistor, get rid of the extra resistor, you don't need it with 3 ohm coil.

 

[Janicholson]

Though a common belief there is no internal resistor in 12v coils.they are just wound with more and smaller wire to operate at 14.4 volts (running system volts) Jim

 

[John T]

1) We did put a new rotor on and the new coil has an internal resistor.

Actually theres no discrete stand alone resistor tucked away inside the can, the necessary total resistance is derived from the windings alone NOT a hidden resistor

2) Was using a digital fluke meter.

Try an old better damped ANALOG meter like my old Simpson 260. With brushes and commutators digital meter may go bonkers lol


3) I think I'll try the suggestion of pulling the main coil wire to see if there is spark there. If so the problem must be in the cap/rotor area, correct?

Ifffffff the coil is firing fine but no spark out the caps coil wire look for a cap or rotor problem and if the rotor tip is properly aligned. I have seen rotor caps develop a short !!!!!!!!!

Have you worked through my Troubleshooting Procedure it can help find the problem

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

Soooooo often burned pitted or oxide coated points is the only problem

John T
John Ts Ignition Troubleshooting

 

[theog9n]

So all is good, we have spark! i believe the rotor was not seated on the shaft all the way. All i did was take off the cap on rotor, put back on and spark appeared. Now on to putting fuel tank back on and see if she will fire up.

thanks for all the suggestions and help. i went over all of that, good learning experience.

 

[Janicholson]

A poorly seated rotor usually hits the terminals in the cap and causes the rotor to be broken, or the drive flats inside the rotor mount to shear. If it has spark, the points were likely disturbed by the cap removal and began conducting again. jim