cherokee no spark

[langer1]

JeepCJ, the small yellow wire is the trigger wire from the ECM, pin D13. This is the wire that pulses for every coil spark. I think it pulses from an open to a ground, to fire the coil. 8Mud metioned that it might pulse from 12v to 0v, so I don't know which it does. Regardless, it should pulse when the engine is turning over. You are right, it should have nothing with only the key on. The engine has to be turning for it to have a signal.

You can try checking for a pulsing voltage on this wire with the starter turning the engine. If you don't get voltage, then check it for a pulsing ground signal. Remember on a Renix, the engine has to turn over two revolutions before this wire will show anything.

CorbinaFly brought up the question of the flexplates. As he stated, the Chrysler flexplate won't work with the Renix electronics. I hope you installed the 89 flexplate......

ROE

Where I see confusion is there has to be a ignition module and a coil, (MSD or what ever brand) the yellow wire from the ECU must go to the module, it can't go stright to the coil.

 

[jeepcj7304]

it has a module with all the same wires going to it and tehn has two coming off from the module to the coil i tried checking the coil the way mentioned but i didnt get spark i assume because there is power on both sides. the garage i took it to a week ago said they switched out coils and it still didnt work

 

[langer1]

it has a module with all the same wires going to it and tehn has two coming off from the module to the coil i tried checking the coil the way mentioned but i didnt get spark i assume because there is power on both sides. the garage i took it to a week ago said they switched out coils and it still didnt work

Ok fine, now you need to check the inputs to the module. If there ok then
the module is bad.

 

[Runnin'OnEmpty]

JeepCJ, the small yellow wire is the trigger wire from the ECM, pin D13. This is the wire that pulses for every coil spark. I think it pulses from an open to a ground, to fire the coil. 8Mud mentioned that it might pulse from 12v to 0v, so I don't know which it does. Regardless, it should pulse when the engine is turning over. You are right, it should have nothing with only the key on. The engine has to be turning for it to have a signal.

Where I see confusion is there has to be a ignition module and a coil, (MSD or what ever brand) the yellow wire from the ECU must go to the module, it can't go stright to the coil.

Yes, the (small) yellow wire is the trigger wire from the ECM, going to the ignition module. It sends the signal to the ICM to fire the coil. This wire would be a good one to check, because if it has voltage, then the trouble is in the ICM or coil (not likely since it's been changed). If there's no voltage, then the trouble is on the other end, in the ECM or a sensor.

It's an easy check. I'd stick a straight pin in the wire, place the (+) voltmeter probe on it, and place the (-) probe to an engine ground. Then, after 2 engine revolutions with the starter, this wire should show a voltage pulse. I'm guessing here, but it'll probably be a 5v pulse.

 

[jeepcj7304]

i am gettign nothing on this wire it has continuity to the ecm and the ecm is new so im still stuck im thinking of taking it to a mechanic around here who deals primarily with electrical problems if i can tfigure it out by wed that is what im going to do any last minute ideas

 

[8Mud]

I just went out and tested everything I could by myself. It's kind of rough getting good contact and turning over the motor at same time, with one person. So I didn't get all the possibilities.
Key on, two pin connector *disconnected* (small yellow wire) 5 volts DC to battery ground. Three pin connector large yellow wire, 13 (12) volts, to the battery ground.
*Coil disconnected* (removed), key on 13 (12) volts at the (firewall side) coil contact on the ignition control module. With all connectors connected.
No voltage reading on the two pin connector (small yellow wire), *with it connected* to the ignition control module and back pinned. I checked both the AC and DC voltage on a digital meter. If there was any voltage there, it was so low to be irrelevant. I guess the module dumps the 5 volt signal to ground, when the two pin connector is connected and the key is in the run position.
With the two pin connector (small yellow wire) connected to the ICM and *back pinned*, motor start (motor turning over), a digital multi meter got twitchy on the voltage numbers DC (10 volt scale) and the voltage numbers really got twitchy in the AC (10 volt scale). The same test with a analog (needle type meter), I tested using both the 2.5 volt scale and the 10 volt scale AC and DC. The needle would twitch once good, then just slightly shake. This is with the coil disconnected. I got better needle movement, with the meter on the AC scale.
I tested a stock XJ *coil*, it was 7 ohms between the two power leads and 4,700 ohms from the plus lead to the high voltage lead and 7,500 ohms form the negative coil lead to the high voltage lead. A coil with lower ohm readings may cause the ICM to overheat and/or fail.
I also tested the coil ground contact in the ICM (everything disconnected and no power), to the ICM ground pin and got 9,200 ohms. And 31,000 ohms between the two coil leads on the ICM, everything disconnected. I tried to read a 12 volt DC pulse, between the two coil connectors, with the motor truning over (connectors connected), with iffy results.