Re: NO FIRE ???

Posted by Joel Wagner on November 28, 2001 at 18:06:54 from (205.188.199.168):

In Reply to: NO FIRE ??? posted by TOM SHERMAN on November 28, 2001 at 13:30:58:

Tom,
I have an inexpensive volt/ohm/amp meter that I bought at Radio Shack for diagnosing these problems. Some good suggestions have already been filed. I would hook your meter ground lead (black usually) to the frame of the tractor (assuming negative ground, other wise use the red lead from the meter to ground) amd touch the other lead to the non-ground battery post. Work your way along the ingition circuit path to the coil by checking various wire locations. This will vverify that the battery is good and all wires are connected correctly through the on/off switch. If you have 12 volts to the coil, continue through the coil to inside the distributor by checking the voltage at the points where the wire is connected. As another has suggested, the volts should be 12 with the points open and close to 0 when closed. If voltage is always 12 or close to 12, check to see if points are adjusted to the correct gap. If they are, clean the crud off the points and recheck. If the volts at the points are always close to 0 (with 12 volts on the hot side of the coil), check for correct point gap and if good then check for short. Sometimes condensers will short out (more on this later). Unhook the battery before conducting any resistance measurements on the ignition, as any voltage on the system to your meter leads while set to the resistance setting will blow a fuse in your meter or worse if there is no fuse. You can check for shorts using your resistance meter set to the lowest setting. If the voltage at the points behaved correctly (0 for closed and 12 for open) and you get no spark, it is time to check the coil.

Unhook all wires to coil. Check one side of the coil by setting resistance meter to lowest ohm setting and measuring resistance across the 2 posts, resistance should be on the order of a fraction of an ohm, say 0.3. If zero, no good, if much greater than an ohm, might not be good. If ok , set resistance meter to a setting to read thousands of ohms, usually the 1k setting is ok. Check resistance from one of the posts to the high voltage output of the coil which goes to the center of the distributor and to the plugs. Resistance should be between 5k and 10k ohms or so. If zero, that's bad, if open to infinity, also bad. (remember to adjust your meter to zero ohms with leads shorted when changing resistance scales)

You can check the condenser with your meter too by setting to highest resistance setting and touching the metal part of the condenser and the lead (unhooked from the points)the meter should move slightly from the ininite reading and then go back again. To recheck, short condenser lead to its metal case and repeat. If the condenser does not read infinity with the meter at its highest setting, get a new condenser.

Well, if all those tests check out ok, you should have spark. If not send me an email.

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