no power to my ignition coil

Joined
Sep 12, 2011
Location
fort bragg
i rebuilt my jeep now i dont have any power to my ignition coil all wires have continuity but no power is there any way to bypass so i do get power or have any ideas on how to get power any help would be nice 1990 yj 4.2 inline 6
 

jeepn-jason

Well-Known Member
Joined
Mar 20, 2005
Location
Greensboro
im pretty sure the duraspark ign module supplies power to the coil on these.
 

Blkvoodoo

professionally useless
Moderator
Joined
Mar 16, 2005
Location
Archer Lodge
using a test LIGHT connect to power wire of coil in question, then crank engine, the light should flash ( quickly ) as engine is cranked. ( connecting to the output of coil will blow the bulb, but it'll be really bright at least once ! )

The coil isn't ON all the time, it is cycled on and off by the ignition module. so just testing static voltage at the coil won't give you anything. this happen VERY fast

connect a timing light lead to the coil wire to distributor, you'll see how fast we are talking when the engine is running.

an ignition coil is like a large capacitor, applying voltage creates a an electrical field ( charging the capacitor ) turning the coil off causes the field to collapse, and if there is a ground path ( spark plug with small gap ) there will be a spark. the distributor just aims the energy field to the respective spark plug in sequence. it also switches the ignitor on and off,

older engines used contact points ( think small mechanical switch ) to do this, newer use a Hall effect sensor ( magnetic switch )


crude but simple explanation of how it works, others may have different ideas

just like you scuffing your feet on the carpet in a dry room, you are the capacitor, touching a metal object is the ground path, and POP, you get shocked ( there is a spark there if you look closely )

new engines with no distributor do the same thing, only the cam and crank sensors are the "switches" the ECM does all the other stuff and is MUCH more precise
 

jeepn-jason

Well-Known Member
Joined
Mar 20, 2005
Location
Greensboro
I may be wrong here but I always thought the distributor sent the negative trigger to the coil and power was just 12v ign?
 
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