We are getting no spark while starting the 4.0 and we tracked it back to the conector at the coil doesnt have 12 volts but everything else does. we had a blown 15a fuse in ign. fuse box replaced hasnt popped again and still have no spark and i cant find an accurate wiring diagram for this jeep
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Replace the coil and ensure that you get the correct coil voltage for the vehicle Coils come in to voltages Straight 12 volt coils that start and run on 12 volts and other that start on 12 volt and run on 7 volts. Check if it needs a resister with it.
check that you have the correct voltage coil installed. IT sounds as if the coil is overheating and failing. There are 2- 12 volt coils on the market. one is a full 12 coil and the other is a duel voltage coil. The wiring allows to start opn 12 volts and as soon as the engine starts runs on 7 volts through a resistor.If you are running a12 volt use with resistor coil on straight 12 volts system you will have problems as you describe
A test light connected across the coil primary leads should flash on + off when engine cranks(coil sparks when 12v turned OFF due to collapse of magnetic field).If you get pulsed 12 volts,and no spark from the coil,the coil is bad.If you don't get the pulsed 12 volts,trace back to find out why(the PCM turns the coil ground on and off,12 volts comes from switched IGN source)
You are at thhe right trail what controls spark is coil pack crank sensor sparkplugs and plug wire but the most important is power . I mean 12 volt connections and ground This includes checking fuses you need a simple volt meter doesnt have to expensive or fancy just to pick up 12 volts let start with fuses in the engine juction box (there not mark to what it belongs to) make sure none are open. especially fuse 19 and 24 , next go to the crank sensor make sure the tabs are snuggly on now to the coil pack there is a red and light green wire this comes from ignition and feeds 12 volts at the coil pack measure that voltage is it 12 volts if not correct it this is from ignition switch ( you can make a tool that feed 12 volt with a wire and a fuse in series and attatch it to battery and the primary wire this is known as hot wire) next go to the ECM wiggle the wires see if that get a connection going if not go back to the ICM here are the wire you are to measure the tan light green, this is from ECM and it is pulsed it measure 5vlts to 0 volts switched then measure the tan orange the same thing 5 volts to zero,then tan white again 5vlts to zero. any one of these 5 to zero fails you fix is the ecm
Follow the number 4 cylinder spark plug wire back to that ignition coil.
Verify that the wiring is getting voltage approx 12 volts with key on and that ground is good
Make sure that the wiring going to that coil is not corroded, broken pins or breaks in wiring
You might not have spark as the 12 volts needs a ballast resistor or the points burn out preytty quick. 8 volts at the coil in run with the points open and 0 with the points clsed and battery voltage at the coil when cranking. coil wire near the intake manifold while cranking should jump at least 2 inches. Closed points should be 0 volts at the neg on the coil. pos and neg should be the same 12 volts with the points open. if not either the coil or the points are bad. The condenser can fail and no spark with all the rest right
check ignition fuse.if okay.remove one of coils connectors using a test light .turn ignition key to on position .terminal 1 on the connector to coil is the first to left with the locking tab up. then remove the ignition module connector terminal 4 is 12 volt supply.4 terminal to the right with lock tab up.connect test light to ground.take the pointed end touch both the terminals for 12 volts with ignition on position.if getting 12 volts.you have PCM PROBLEMS OR CRANK POSITION SENSOR..IF GETTING NO 12 VOLTS YOU GOT A BLOWN FUSE OR GROUNDING PROBLEMS.