Hi i need help!!!! I now this is a old topic but i new in the cherokee world....
my 96 xj dont start. Well i changed the CKP but no start. i check the sparks plugs and everyting and i notice no sparks what so ever. Please advise...

 

No plugs? That's the problem. Go to the parts store & get some.

Report back.

What is a CKP?

 

Lol.

 

http://jeep-xj.info/HowtoECUcodes.htmRead...

 

No sparks. I thought you typed no spark plugs.

Coil, coil wire, dist. button, or CPS (crankshaft position sensor).

 

1. First, swap the ASD relay in the power distribution center (black box under the hood) with another non-critical relay.

2. Test your ignition coil. They can be tested for both primary and secondary resistances.

3. Below is more on the route of spark on the 4.0 H.O engine.

Spark: 12 volts from ignition switch to the ASD relay; when the key is first turned on the PCM provides a ground to the ASD relay to energize it, then the ASD relay passes 12 volts to the coil primary side. If no crank sensor signal is generated after a couple of seconds the PCM cuts the ground to the ASD relay (and fuel pump relay too) and that cuts power to the coil (and fuel pump). Key to START and once again the PCM energizes the ASD relay. Now, a critical element is the crank sensor--no signal from the crank sensor and the PCM won't trigger the coil to provide spark.

 

What about fuel pressure at the rail, and signal to injectors?

Not hijacking the thread, but currently having the same problem after a series of stalls on the freeway and a HUGE freaking backfire....

I worked in order from the takeup coil (CamPS) to the ECM, in addition to CrankPS, Coil, etc... All good. Replaced with all new parts. Heading back to test again today.

Maybe a coincidence, but this happened shortly after installing a new starter. Can't imagine why that would matter.

JW

 

Fuel pressure shoudl be 50psi @ key on
and should hold @ 50psi

What year Jeep?

 

Mine's 98, 4.0, 5-spd, 297K miles. I have pressure at the rail. There is no electronic signal to the injectors to fire. Point is that pressure at the rail doesn't necessarily mean the injectors are working.

JW

 

sorry guys for i didn't explain my self clear. I changed de crank sensor. the fuel pump works fine and i have presure at the fuel rail. but no sparks.

 

What brand of CPS did you get?

Many of the parts house CPS's are bad right out of the box. That's one place you want to go with a dealership part if at all possible.

 

Pressure at the line doesnt mean its going to work either.
Has to be around 50psi

Easy place to start is to crank it a few times then pull a plug-
wet= with fuel its a no spark
dry= its a fuel issue

 

I'll start my own thread, but as problems are similar to ozzydog, thought I'd post here as well.

Summarry:
98 XJ - 5spd - 293,000miles
Engine died on freeway, similar to as if the CPS failed. Restarted for another mile, sputtered, HUGE backfire, then stalled. Towed.
Have crank with no spark and no signal to injectors. Fuel rail at 49psi.
ASD - test good.
CamPS - volt/ohm check tests good.
CkPS - volt/ohm test good.
Coil - bench tests good.
AllData Dx tree suggest replacing the pcm.
Still no start.
Bought a code reader - both pcms are throwing P0351 (primary coil circuit code). Troubleshooting that circuit shows no shorts and good voltage.
Old pcm was throwing the CamPS and CkPS codes. After erasing these codes, they aren't back again. Just the P0351 coil circuit code.

Could I have jumped teeth on the timing chain during that backfire?
This then causing either the CamPS or CkPS to halt the engine?

 

So it turns out that the coil, the CPS, and the CamPS all went at once.

So my thinking is the CPS went, causing the shutdown on the interstate. The coil must have gone then as well, b/c the first thing I did to repair was to replace the CPS. Then I had crank - no start - no spark - and no voltage to the injectors.
Switching relays with ASD caused no change.
Coil bench tested fine, so assumed it was OK.
Tested CamPS voltage during crank, it was OK.
So must be the PCM. New PCM = no change.
Bought a scanner for $50 at AZ.
New computer was throwing a Primary coil circuit code and a failure to read TCM code (I have a manual...so couldn't figure that out)
Old computer was throwing CPS code, CamPS code, and Primary coil circuit code - still in the PCM from engine failure.
Erased codes from old computer, cranked the engine for a while and reread. Threw CamPS code and Primary Coil Circuit code again.
New CamPS took care of the former. Still tried to troubleshoot the coil circuit -other than the coil- as the original bench tested fine.
The next steps in the ALLdata testing process involved building some crazy three pronged capacitor jumper and shorting things out. I figured for that effort I might as well buy a new coil before spending that much time and money. Sure enough...it started after installing the new coil - which by the way - bench tests exactly the same as the old coil. Tried starting with the old CamPS, and it started, but threw same CamPS code with the old one installed.
So new CPS, Coil and CamPS.
Anyone ever had all three go at once?
Returned new PCM, so I'm only out a few parts and some time. Got a scanner to boot.
Thanks for the suggestions...
JW