cherokee no spark

i have an 89 cherokee i swaped the block and head from a 96 in and all the sensors are from the 89 along with manifolds and injection. i cant get any spark put a new crank sensor in and i get no spark. i have power on both sided of the coil when ignition is on and while crancking i have located a violet wire running from a conector near the battery along the fire wall and over about midway down the intake manifold it has full voltage when ignition is on. i really cant figure out this frigin gremlin i need help fast any ideas could it be the auto shut down relay? im really stuck and my wife needs her cherokee back its been down a month now.

i went an ordered a computer today hopefully it will fix it (fingers croosed)

A short class in ignition and ignition coil.
The coil is actually a transformer (with two coils inside), it takes 12 volts and turns it into 30,000 volts or whatever.
It does this by saturating, one coil with 12 volt +. The ignition control module (by signal from the ECU) completes the ground circuit, collapsing the winding (magnetic field) in one coil. This produces a current in the second winding, in this case 30-35,000 volts or so.
The signal from the ECU to the ignition control module, telling the module when to ground the coil, is a square wave, almost alternating current. I´m gonna get a bit technical, disregard if it doesn't make any sense. The book says it is a square wave, they don`t say if it is an alternating (full) square wave or half square wave. They also don't say the direction of flow, if it is a half wave, direction of flow is kind of irrelevant though.
There was a warning ( I read about 12-15 years ago) about poking around the small yellow wire, the ECU to ignition module signal wire (or in my vernacular, trigger wire). With the wrong meter, it may damage the circuit. A digital meter (on the AC volt scale, while cranking the motor), should be OK, but who knows for sure. Personally, I've rarely been brave enough to try it. I always switch my meter to the AC volt scale, when testing a pulse circuit.
If the ECU, isn't receiving the proper inputs, it's doubtful it will trigger the ignition module.
Seems Renix and OBD 1 motors, use there own flywheel (or flex plate), with different notches and actually different CPS's to input the ECU.
There is a whole list of inputs, the ECU needs to start the motor. One of the most important, is the CPS and the CPS has to give the ECU, usable information. If the pulse signal fro the CPS is too far out of the box, it's doubtful the ECU is gonna trigger, the ignition control module. If the CPS isn't working properly, it's doubtful the injectors are gonna cycle. The injectors are 12 volts, to best of my knowledge, should be easy to check any colored wire to the injector, 12 volt DC (probably easier with a needle type meter) to vehicle ground and see on the meter if the injector cycles (during cranking). If the injector cycles and the ignition module doesn't fire, you've really narrowed down the possibilities. If the injectors aren't cycling and the iginiton isn`t firing, most probably it's in a sensor circuit or a 12 volt power circuit or even a ground circuit.
If any of my explanation is flawed please chime in. Some of this is just personal theory, that I've never had to test.
Doing it and writing about it are two different things. I have a picture in my mind of the loops and sub systems and generally test somewhere near the center of each loop and/or sub system and generally find the problem quick. Sensor circuits are a whole other can of worms.
What did you do with the knock sensor? And the engine temperature sensor in the lower left block?

i have power on both sided of the coil when ignition is on and while crancking

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JeepCJ, I think something's wrong here. As 8Mud alluded to, the negative coil terminal is where the coil is grounded to allow it to spark. Since you have voltage on the negative terminal, you must have the wrong wire connected to the terminal, or a short circuit in the ignition module.

If it was a CPS or CamPS problem, I think you'd see 0v at the coil negative terminal, instead of 12v. That puzzles me. Honestly, the only thing that comes to mind is a short in the igniton module (connected to the coil on the REnix). I'll look at some wiring diagrams and get back to ya.....

Runnin'OnEmpty said:

JeepCJ, I think something's wrong here. As 8Mud alluded to, the negative coil terminal is where the coil is grounded to allow it to spark. Since you have voltage on the negative terminal, you must have the wrong wire connected to the terminal, or a short circuit in the ignition module.

If it was a CPS or CamPS problem, I think you'd see 0v at the coil negative terminal, instead of 12v. That puzzles me. Honestly, the only thing that comes to mind is a short in the igniton module (connected to the coil on the REnix). I'll look at some wiring diagrams and get back to ya.....

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Don't get the ignition control module and the coil confused they are bolted together but seperate.
There is (to the best of my recollection) only four wires to the ignition control module. The large yellow, which is power in, key in the run or start possition. The small yellow wire which is the trigger wire (from the ECU), the black which is ground and the green which is the tach.
If there is voltage on the black wire, the ground is poor or non exsistant. With the ground disconnected there may be some voltage on the wire, but this just may be the ground part of the electronics circuit.
The coil uses quit a bit of amperage. The ignition control module, grounds the coil, through some rather robust circuitry.

8Mud, I just pulled apart an extra Renix coil/module that I had in the garage. It has 3 plugs: a 2-wire, a 3-wire, and a single spade connector going directly to the coil. The single spade is marked +, and the right coil connector is also marked +. The negative terminal is on the left, and it has a hole in the unit, probably for testing......? I sold my Renix XJ recently, so I don't know how the wiring routes.

It dosen't look like it can be wired incorrectly, assuming the stock connectors are used, so that rules out one thing at least.

JeepCJ, what terminals did you touch to get the 12v on both sides of the coil?

Here's a test you can do:
Pull the coil to distributor wire out of the coil about 1/4", and ground the other (distributor) end. Then, with the key on, touch a grounded wire to the terminal that's inside the plastic port (mentioned above). That's the coil ground terminal. As you touch the terminal, you should hear a spark jump the gap at the loose coil/distributor wire. This tests the coil, if it's good then we go on to something else.....

the coil was never disconected everything worked before with some more searching i found what appears to be a sensor that goes into the head on the left side of the motor right near the valve cover on the drivers side near the firewall there is no wire running to it and really not sure what this is or what it does this may be my problem also the violet wire i looked at some diagrams but the only one it shoes goes to the map sensor and there is one going there could it go to this sensor any one have a older cherokee it starts at a connector by relay box and goes along the fire wall not sure where it is suppose to go there are like 4 wires on the connector

Rear drivers side of the head rear. pointing up is the temp. sender for the gauge. Stick around for a few, I have an extra harness in the garage and will look at the connector you mentioned.
How many pins in the connector? I´m not seeing a four wire. There is a flat three pin connector, mine is green.
Using the oval rubber grommet (at the firewall) for the ECU harness is the connector left or right as you face the motor from the front?

Is it possible you plugged the black three pin connector (two pins, 2 wires) from the injector harness (actually the CPS plug) into yout MAP and the map plug (three pins three wires violet, red and brown) into the injector harness?

I believe the the coil fires when the supply voltage to it is opened. Not the other way around. So when the ignition is on there should be a +12v and a ground to the coil. The ECM fires the coil by breaking the ground or +12v circuit. Someone let me know if I'm loco here.
As 8mud said, the sensor on the rear of the head is for the temp gauge. It's not your problem.
Did you only change the block and head, or did you change the flywheel or flexplate too? The renix and OBDII (96) are different and the cps for them are different too. So if you're using your renix ECM, you need to have your original flywheel on.

K

I looked at the harness (and I am a bit color impaired) the wire to the temp. sender for the gauge is faded violet. It has an elbow shaped connector on the end.
Your 89 may have a slightly different harness than mine, but there is a purple (violet wire running through a ten place (9 pin) connector (near the relays), that ends up at the temp. sender for the gauge.
The four pin connector (near the relay block) on mine doesn't have a purple or violet wire, but does have a faded red wire that is the power for the latch relay.

corbinafly said:

I believe the the coil fires when the supply voltage to it is opened. Not the other way around. So when the ignition is on there should be a +12v and a ground to the coil. The ECM fires the coil by breaking the ground or +12v circuit. Someone let me know if I'm loco here.
As 8mud said, the sensor on the rear of the head is for the temp gauge. It's not your problem.
Did you only change the block and head, or did you change the flywheel or flexplate too? The renix and OBDII (96) are different and the cps for them are different too. So if you're using your renix ECM, you need to have your original flywheel on.

K

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The way I understand it, I think maybe you are correct, my explanation was a holdover from the old coil and points days.
Think the Jeep coil is pulsed by a square wave, it is said, it fills (or saturates) the coil and then interrupts the power supply, collapsing the field. The leading edge of the square wave fills the coil then the trailing edge of the square wave collapses the coil (to ground?). Though this explanation also sucks.
But the point I was trying to make was the smaller yellow wire is the trigger wire, and pulses in a square wave, that may be hard to read (and even possibly dangerous to try) with a low impedance DC meter.
What makes it work is building a field, then collapsing the field, which generates high voltage.
The large yellow wire is the main power for the whole operation and the small yellow wire is a 5 volt (about) square wave trigger. The ECU needs some inputs to generate the pulse (at the right moment), like the CPS. And needs some base information, like the MAP readings for atmosheric pressure and others to set the ignition timing for startup.
I have an extra coil and module that I bought like 17 years ago, just in case, and have never used. Also have an extra ECU, that has been collecting dust forever.

ok here is where i stand the coil is an msd that was put on by the previous owner i tried touching a ground to the negative side but got nothing but a spark at the post because both are hot i have the four wires going into the ignition control module then two coming off the top of that to my coil mounted on hte fire wall i have a good ground on hte black wire and a good power on hte large yellow the green is dead because its not running and the small yellow im getting nothing at on no ground or power i tried a computer i hadlying around and it was the same i am going to pick up a new one in a few i might grab a coil at the same time well if anyone thinks of anything i am still screwed at the moment

also i just noticed what i think is my crank sensor is broken would this cause this problem also i dont have an oxygen sensor hooked up yet could this also be a problem

jeepcj7304 said:

also i just noticed what i think is my crank sensor is broken would this cause this problem also i dont have an oxygen sensor hooked up yet could this also be a problem

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If the CPS is broken you will not get any spark. I thought you said that you put in a new one. Did you accidentally break it? I would change that before trying anything else.
You'll need the O2 sensor hooked up for the motor to run properly. But you should be able to start it without it. It will just run like crap.

K

sorry its not the crank sensor its the knock sensor i had cps on hte brain the knock sensor is broken it just pulled the connection off th esensor i pushed it back on pretty sure its getting through ok i hooked up the new computer no change i looked at a service manual and it says about checking sync signal i tried this and got no voltage but the theory doesnt seem sound can someone do this check on a running xj and se if they get what this says please here is the test

it says put the + volt meter lead into the blue wire of the distributor connector

put the - lead into the gray /blk tracer wire of connector
do not disconnect insert into back side to make contact

turn the ignition to on and you should see 5 volts

i get none if i put the positive on those and the negative on the battery i get 2 volts on the grey and 7 on the blue someone try this let me know what they get thanks

I just tested mine and had some trouble getting a good connection with the meter leads. I used an exacto knife to cut a couple of slits in the blue and grey wires and made my test that way. Sealed the cut with a dab of silicon when finished.
Your only gonna get a voltage if the stator is in the right position. You have to test it with the connector connected, the coil wire removed and the engine cranking (not running).
You may be able to turn the motor over by hand and read your voltage that way also. I just look for the pulse, which is hard to read on a digital meter, but shows up well on a needle type meter.
I´m pretty sure the sync sensor isn't, gonna cause a no spark, I ran mine for a week once with the sync sensor disconnected and didn't even notice a difference.
By the way, I went out and pulled a bunch of various connectors on mine this morning, trying to figure out what would cause a no spark. The CPS connector, the grey square connector near the brake booster and the six wire connector next to the fuse block, where the only ones that affected my spark. I imagine the large connector block, on the firewall behind the fuse block would also do it, but I wasn't that curious. Some of my connectors may be different, mine is an 88. I also may have missed something.
There are two power sources for the ECU, one from the ignition switch and one from a fusible link on the starter realy. I really don't know what would happen if one or the other was disconnected, had an open circuit or a bad fusible link. Just an idea.
I´d do a continuity (ohm) check from the CPS connector all the way to the ECU connector. Just to eliminate that as a possible problem.
You never did say which flex plate (or flywheel) you have on the motor, the early or the late model.

it has the 89 flex plate on it

The voltages and pinouts you were given to check were for the spark module not the coil, go back and start there.

ok here is where i stand the coil is an msd that was put on by the previous owner i tried touching a ground to the negative side but got nothing but a spark at the post because both are hot i have the four wires going into the ignition control module then two coming off the top of that to my coil mounted on hte fire wall i have a good ground on hte black wire and a good power on hte large yellow the green is dead because its not running and the small yellow im getting nothing at on no ground or power i tried a computer i hadlying around and it was the same i am going to pick up a new one in a few i might grab a coil at the same time well if anyone thinks of anything i am still screwed at the moment

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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