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Power Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Tue, 10 Jul 2007 13:39:28
In Reply to: spark/no spark, Kurt Meyer, Tue, 10 Jul 2007 09:58:51 Members do not see ads below this line. - Help Keep This Site Online - Signup |
When you say power to the coil, I assume you mean 12 volts to the green/white lead (high side of coil). That side is connected to power (fuse 3) whenever the key is in the ON position. If that voltage is going away, the problem isn't the ignition.
Check the voltage on fuse 3, and see what happens when you turn the key to ON. It should be there all the time. If it is going away, I would suspect a problem with the +15 bus contacts on the ignition switch. You turn the key to ON and you get voltage to the high side of the coil. That's not much of an electrical load. After a couple of seconds, something else on that voltage bus cuts in, and the extra current through the poor connection (resistance) in the ignition switch causes a voltage drop.
Now, if you are talking about the Blue wire off the switch, that is a different matter. That is the low side of the coil. The ignition amplifier switches that to ground. So if the voltage on the blue wire is +12 volts, then the IA isn't switching it to ground. The way the IA should work is that it ties the low side of the coil to ground for most of the time (this builds up the magnetic field in the coil) and when it opens (low side jumps up), the magnetic field collapses and this causes the spark. So it's reasonable that the low side should be, well, close to zero most of the time. If you are using a digital meter, the low side will show pretty close to zero when cranking, because it will average the near zero volts (probably around 0.5 to 0.7) when the IA is tying the low side to ground with the open of the coil (clamped at +12). So the low side might look more like 0.5 to 1.0 volts when the engine is cranking.
posted by 192.249....
, Tue, 10 Jul 2007 13:39:28 <-- Viewing This Message
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