No spark! Thoughts? -
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Unread 07-12-2012, 11:11 PM   #1
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1999 XJ Cherokee 
Join Date: Jul 2012
Location: Philadelphia, PA
Posts: 3
No spark! Thoughts?

I have a '99 Cherokee Limited. On Sunday, I topped off both my steering fluid and gas tank and it ran great. Went to start it Monday and it turns over, sounds normal, but will not fire. Tried to start in neutral, no dice. Definitely not the battery, so I bought an ignition spark tester and there is no spark from the coil wire or any other plug wire. I also replaced the distributor rotor and cap and was excited to see the old ones all corroded and beat up and thought I found the problem, but that still did not fix it.

It just hit 115k miles and I have owned since 70k and have not had the spark plugs replaced, for all I know it may still have the originals. That is next on my to do list whether it will fix this problem or not. I've read stuff about the timing chain, but I don't even know where to find it....very new to this, please be gentle. Any thoughts you guys may have will be greatly appreciated.

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Unread 07-12-2012, 11:14 PM   #2
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1998 XJ Cherokee 
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Check you crank position sensor (CPS). Search for a method to test it. Super common failure.
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Unread 07-12-2012, 11:47 PM   #3
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1993 XJ Cherokee 
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Check your coil pack
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Unread 07-13-2012, 06:09 AM   #4
It's the crank sensor!
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1999 XJ Cherokee 
Join Date: Nov 2007
Location: Central Minnesota, MN
Posts: 8,432
If you're sure you have no spark, the #1 cause of that on the Jeep 4.0 engine is the crankshaft position sensor. The #2 cause is the ignition coil, but those fail less often than the crank sensor.

They both can be tested and while testing of the coil is normally conclusive, testing of the crank sensor isn't always accurate.

Because it's easy to test a coil (you'll need a meter and a manual with the resistance specs), I'd start with that. If that checks good, although there still are other suspects, it might be time for a crank sensor. If you get one, do yourself a favor and buy a Mopar unit directly from a Jeep dealer or from a company like moparpartsonline which sells genuine Mopar parts at a discount. I bought a crank sensor a few months ago for my 99 for not much over $50.

Good luck!
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.
99 Cherokee, 4.0 AW4, NP242
Past Jeeps: 49 Willys, 81 Scrambler, 88 Comanche
Without "data", all you have is an opinion!
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Unread 07-13-2012, 06:06 PM   #5
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1999 XJ Cherokee 
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Thanks for the responses so far. I haven't done anything new to it yet, but I did find this thread which may be helpful for people who find this thread in the future......
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Unread 07-13-2012, 08:24 PM   #6
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2000 XJ Cherokee 
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Deff check or replace the cps. Bleed the test port of the fuel rail, then prime it, if there is no pressure, I would think the cps. Least that's how it went with my 96

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Unread 07-15-2012, 07:27 PM   #7
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1995 XJ Cherokee 
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I had same issue with my 95 Cherokee, replaced coil, dist cap,rotor, wires and plugs. I was going nuts until I read this thread. Replaced the crankshaft position sensor and it fired right up.

Thank You

Ranger Dave
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Unread 07-17-2012, 08:37 AM   #8
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1999 XJ Cherokee 
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Glad you got yours fixed Ranger.

As far as buying original Mopar parts, there doesn't seem to be any sites carrying a CPS for an '99 automatic. This leaves me with the super cheap Amazon option ( or the still fairly cheap option from 1aauto ( Anybody have any experience with either of these, or suggestions on how to find original parts?

Also, here is another useful link for this same problem:
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distributor , ignition , no start , spark
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