- Reply to Topic
Thread: zj crank no spark Reply to Thread

Register Now

In order to be able to post messages on the forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter a valid e-mail address for yourself.

Email Address:


  Additional Options
Miscellaneous Options

  Topic Review (Newest First)
01-14-2020 11:20 AM
robertmichiels I tested the ASD relay and tried the bypass trick because someone in this thread mentioned it when I first posted on here. Last night I was able to get it running. But its missing really bad. I still have the code P0340. The camshaft position sensor is factory, brand new from Mopar (Jeep) The camshaft position sensor is built into the distributor and that is brand new (off brand) from Autozone. I have tested the wiring harness to the PCM and I have perfect wires and connectors.

I called Mintt the company that I got the PCM from. When I gave them my order number they said, "oh is this for the 2000 jeep grand cherokee?" and I said, "No, its for a 1998 Jeep Grand Cherokee" They said they are going to send a new PCM right away.

I will keep you posted on what happens when the new one comes in.
01-13-2020 08:24 PM
Installed the new PCM...Now it is running like crap...

Originally Posted by watertrucker View Post
Had exactly the same issue with my’98 ZJ 4.0 Ended up being the PCM. Seems like you covered all your bases so hopefully your new PCM will solve your problem. Let us know how your PCM front Mintt works out.
Good news is, the new PCM came in the mail. I installed it, and still crank no spark at first. Threw a "P0340 code. So I went a picked up a new crankshaft position sensor from Jeep. I read somewhere that the cheep ones don't work most of the time. Put that in, was hopeful that it was going to fire up right away, and still crank no spark. Its weird because there is almost enough voltage going into the coil. But still no start.

I went to work, and before I left put the battery on the tender and charged it all day. (New battery) btw. When I got home, I checked all the leads in the wire harness between the sensors on the crankshaft position sensor, camshaft position sensor, and coil just to make sure that I didn't have a wiring issue, and every wire checked out perfect. (continuity)

I plugged everything back in and cranked...It sputtered and kicked and fired up. It was jumping around a bit, and was not happy but we had combustion. I turned it off so I could go get the GoPro. Documenting the whole thing for my channel. When I came back to crank it over, back to zero again. Crank won't start. I cranked until the battery got low again, and decided to stop, let it set and go to the store for about 45 minutes.

When I got back it fired up on the first crank. This time I tried to drive it down the street. It was backfiring down the road. It did not like when I gave it gas. I pulled back into the driveway and parked in in the garage. After I turned it off, and tried to start it again, it was cranking but not starting again.

I feel like I am going in the right direction, but still am not sure what is going on here. Not sure if the P0340 code will clear itself if everything on that circuit is good. I still have the check engine light. I have a cheep little OBD II scanner. It says that there are 2 codes, but when I check the freeze frame it only shows the P0340 code.
01-13-2020 06:01 PM
V8GCZJ Pcm needs inputs from both crank and cam sensors before it gives spark or pulse for the injectors. Motor need to make at least one complete rotation before this happens.
01-13-2020 03:00 PM
jimdavis577 as stated above you need to check the ASD relay, Down a dirty "quick fix " FOR TESTING ONLY would be to jump the 30 and 87 terminals on the relay and try to start ..... IF it does then either your ASD relay is bad, Or either the control circuit to the ASD or the controlled circuit of the ASD has issues. Another good test that a lot dont know..... Is if while you are cranking the motor look at the TACH , IF it moves, then that means the Cam/ crank sensors are working and its something else, IF it doesn't then you have something in those sensors and that is keeping the ASD from energizing allowing the motor to run, I would also bet if you put a Noid light on an injector, you will see that there is no firing of the injectors as well as no spark !
01-12-2020 02:06 PM
mukluk P0340 means the PCM isn't seeing a camshaft sensor signal despite getting a crank sensor signal -- you're messing with the wrong sensor.

To clear up a misconception you seem to have concerning the coil: power comes from the PDC, passes through the contacts of the ASD relay when it is energised on, then goes to the coil -- the PCM controls the coil by switching the path to ground on/off via the driver wire. The PCM does not provide power to the coil at any time, it provides a switched ground path. With the ASD relay energised or a jumper installed in the empty ASD relay socket from terminal 30 (or B16) to terminal 87 (or B17), you should have battery voltage at the coil connector terminal 2 (DG/OR wire). If you then crank the engine, you should see a pulsing on/off path to ground at the coil connector terminal 1 (GY/WT wire). An easy check to perform is to insert the probes of a test light into the coil connector's two terminals and crank the engine -- the test light should quickly flash on/off while you are operating the starter. You can manually test the coil for function by positioning the coil high tension lead a quarter inch or so away from the engine block, providing 12v from the battery to terminal 2 on the coil, touching a ground wire to terminal 1 momentarily and then pulling the ground wire away from terminal 1 -- the coil should spark as soon as you pull the ground wire away. You can read more information at the link HERE to better understand how an ignition system works. Keep in mind the PCM's internal circuitry takes the place of the old contact/breaker points to control ignition dwell.
01-12-2020 10:39 AM
Update (loosing)

New PCM came in. Plugged everything in, connected the battery and still crank no spark. It threw a code P0340 (Crank Shaft Position Sensor). So I took the new one that I had just purchased back to Autozone and told them that it instantly threw the code. Got my $35 dollars back. Drove 30 minutes to the Jeep dealer and picked up a new crank shaft position sensor. $150.00 Plugged that in, still got a code P0340, still crank no start. When testing for spark pre-coil (from PCM) per the service manual, I get 10.00v while cranking. Checked the ohms on the coil and it falls inside the range in the book. 0.95-1.8 ohms for the primary and 13.0 when I tested across the coil. Still not getting spark out of the coil. Just for the sake of the cost of the part, I changed out the ASD Relay. $10.00 Still no spark. I am dead in the water. Not sure what I should do...

Not sure what kind of voltage I should be seeing when cranking at pre-coil. white 12.4v green ground. When cranking 10.0-9.0 is what I am getting.

I also checked the wire from the PCM connector to the coil connector and it is perfect. (A7)

BTW, spent some time cleaning up all the grounds that I could find.
01-07-2020 12:55 PM
watertrucker Had exactly the same issue with my’98 ZJ 4.0 Ended up being the PCM. Seems like you covered all your bases so hopefully your new PCM will solve your problem. Let us know how your PCM front Mintt works out.
01-06-2020 11:47 AM
robertmichiels The first thing that I did was checked my ASD Relay and circuits and all fuses. (Can't post link here because I am too new.) The ASD relay and circuit was doing what it is supposed to.

From what I have read, when you get weird voltages from the PCM to your coil it means one of two things, you have a bad ground or bad connection in the board or cold joints.

Checked voltage from my PCM to my coil. 10.5v. Then I checked for spark with a spark plug I pulled out of my XJ. No spark. The coil is new, the distributor is brand new, so my cap and rotor are good.

The reason that I went for the PCM is because when I bought this Jeep, it had PCM problems from the get go. (Sending false messages to the display center i.e. brake lights out etc.)When I opened it up after all the testing on everything else, I found cold joints. I did my best at soldiering the loose/ cold joint 2 years ago, and it worked for 2 years, but sure enough the pins that carry 5v (The two all the way to the left), when you open the PCM, had no continuity from the pin to the resistors/micro chips. I soldiered it back and had continuity. Thought I was good to go, but still no spark.

I was convinced that the back of the connection where the pins meet the main had cold joints so I heated up the gel and pulled the whole board out and checked the back side. Sure enough I had cold solder joints on the same pins! Somewhere along the way, I put too much pressure on the board while removing it and cracked something. I was getting frustrated and high off of the acetone so I wasn't exactly taking my time. After I put everything back together, I no longer had a fuel level. I can hear the fuel pump pre-pump, but nothing on the gauge and still no spark. I am going to clean up all my grounds when I get home from work today, and I have a new PCM on order from Mintt ($185). There is not much else to this engine.

I am no master mechanic, but I did end up finding the full service manual for my ZJ for the wiring diagrams. I am going to check on the connections that go into the PCM before I plug everything back in just to make sure. I just needed to cross over the numbers on each pin for testing the PCM. (Want to check the circuit to the fuel pump and float)

Just a recap- changed the fuel pump because it was going bad anyway (original) 195k and was sending a, changed the crankshaft position sensor because that was what went bad on my XJ and it was original, changed the distributor, camshaft position sensor because I broke the screws off on the old one and wasn't sure if I had good connection, and I installed a new coil.
01-05-2020 09:28 AM
jtec WHAT !!

A common no start, mukluk had suggestions, you tested WHAT and jump to PCM and give up?

unplug coil - probe wire - what is voltage ? Place test light into each terminal of coil harness connector - crank engine did yur yest light flash?
01-05-2020 09:04 AM
robertmichiels Last night performed brain surgery on the PCM. After I reinstalled it, I had no fuel level reading and still no start. I ordered a new PCM from Mintt. Going to try that. If it starts, I am going to drive it out to the desert and use it for a back stop.
01-04-2020 01:32 PM
jtec still working this ?
01-04-2020 10:12 AM
Originally Posted by watertrucker View Post
If you could post what year your ZJ is and what engine you have that would help.
Its a 1998 ZJ 4.0 6
01-02-2020 10:37 PM
Originally Posted by robertmichiels View Post
When I check the voltage from the coil I get 10.5 v dc.
You should be getting close to full battery voltage to the coil (voltage from the coil, ie, going to the distributor, should be in the tens of thousands of volts). If the Jeep's starter cranks the engine strongly, then it sounds to me like you either have some dirty/loose electrical connections or bad contacts in your ASD relay.
01-02-2020 11:01 AM
watertrucker If you could post what year your ZJ is and what engine you have that would help.
01-01-2020 05:46 PM
zj crank no spark

I was leaving down town when my jeep died after leaving work. Sputtered, then would not start. There was a few seconds where it sounded like it was going to try to fire, or back fire...then nothing. Towed it home. $120 Thought it was fuel pump. Changed it. $120. Still no spark. (needed to change it anyway because of bad readings on fuel amounts. Also stopped smelling fuel while I was cranking waiting for the tow truck.)

Changed the crankshaft position sensor $40 still no spark. 2 years ago, broke screw on the side of my distributor. Was able to make it work. Thought my camshaft sensor might be bad, so I changed the whole distributor. (didn't have a good seal at the cap) $120 changed wires too. $27 Still crank no spark. When I check the voltage from the coil I get 10.5 v dc. But no spark to the plugs. Checked and double checked that my distributor was installed correctly. (cylinder 1 top dead center, base of crank shaft at 11 o'clock, lined up with pin turned to 1 o'clock and installed perfectly.) Not sure where to look next. I am not getting any codes...

thanks for taking the time to read this. I may take the jeep to mechanic...I just hate to do that because I should be able to fix anything with the tools I have...

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

For the best viewing experience please update your browser to Google Chrome