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Unread 11-04-2008, 02:12 PM   #1
csfiend
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98 4.0 Cranks but no spark at coil

98 XJ 4.0, auto.

I went out to my Jeep this morning to go to work and it'll crank and crank but not start. I have fuel pressure at the rail. I checked for spark and I have none, even at the coil. Pulled the coil out and found a crack in one of the corners, so I replaced it due to the crack and the lack of spark at the coil. Still have no spark at the coil. I swapped the ASD relay with a known good unit, no start. I haven't checked anything else as I needed to get to work.

What would be the next thing to check, and how would I check it? I used to be a technician for a few years, but I don't have access to any of the wiring schematics or diagnostic flowcharts that I normally would use so any help is appreciated.

Thanks!

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Unread 11-04-2008, 02:28 PM   #2
johnsoninc86
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Your CPS is bad. There is a way to test it. I think you have to test the resistance between pole 1 and 2, not sure though. Do a search and you should be able to come up with it, but that definately sounds like a CPS.
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Unread 11-04-2008, 02:36 PM   #3
Stormwalker
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Quote:
Originally Posted by johnsoninc86 View Post
Your CPS is bad. There is a way to test it. I think you have to test the resistance between pole 1 and 2, not sure though. Do a search and you should be able to come up with it, but that definately sounds like a CPS.
That's exactly what I told him when I gave him a ride to work!
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Unread 11-04-2008, 02:46 PM   #4
csfiend
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Hey, I wasn't doubting you one bit, but like I said earlier -- I need to be able to prove something is wrong before I'm comfortable replacing it.
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Unread 11-04-2008, 04:20 PM   #5
tjwalker
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Here's the procedure for testing the CPS on the Jeep 4.0......Good Luck!

CPS TESTING PROCEDURE 1991 – 2001 4.0L H.O. engines

1. Near the rear of intake manifold, disconnect sensor pigtail harness connector from main wiring harness.
2. Place an ohmmeter across terminals B and C (A-B-C looking into connector left to right with the part with the notch in the middle on the right) Ohmmeter should be set to 1K-to-1OK scale for this test.
3. The meter reading should be open (infinite resistance). Replace sensor if a low resistance is indicated.

CPS TESTING PROCECURE for 1987 – 1990 4.0 L engines

Test # 1

Get a volt/ohm meter and set it to read 0 - 500 ohms. Unplug the CPS and measure across the CPS connector's A & B leads. Your meter should show a CPS resistance of between 125 - 275 ohms. If the CPS is out of that range by much, replace it.


Test # 2

You'll need a helper for this one. Set the volt/ohm meter to read 0 - 5 AC volts or the closest AC Volts scale your meter has to this range. Measure across the CPS leads for voltage generated as your helper cranks the engine. (The engine can't fire up without the CPS connected but watch for moving parts just the same!) The meter should show .5 - .8 VAC when cranking. (That's between 1/2 and 1 volt AC.) If it's below .5vac, replace it.
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Unread 11-04-2008, 08:30 PM   #6
HighCountry
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It is such a no brainer... IF you are serious about keeping the Jeep, you WILL need both a Crank Sensor and a Cam Sensor some time in the future. If you just buy them both and stash them below the back seat along with the tools it takes to change them, it will save you a Wrecker Charge some day.

I always recommend doing a quick Test change of the Cam Sensor before swapping the Crank Sensor since it takes a couple of minutes and only requires a Phillips Screwdriver.

Later, Bruce
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Unread 11-05-2008, 01:52 PM   #7
csfiend
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Surprise, surprise -- new CPS sensor and it fired right up.

Regarding the above post, I don't remember the range of years but in 98 at least the cam sensor only controls fuel injector timing, NOT spark.
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Unread 11-05-2008, 08:25 PM   #8
johnsoninc86
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glad you got er fixed!
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Unread 11-06-2008, 09:09 AM   #9
csfiend
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glad you got er fixed!
meeeee too

thanks for your help!
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Unread 04-18-2009, 02:34 PM   #10
opusgamma
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Hi guys sorry to highjack this thread..but i might be having the same problem and here in Dominican Republic are not that many Mechanic that know how to deal with XJ...
I just did an enginge change from a 88 4.0l to a 2002 4.0 ho I left its old fule rail and al lthe electric so i did not need ot do any electrical work but know it turn and i get no spark just like the Op.. can some one telll me what is the CPS and where is located pelase so can do the test sugest on top.
thank
Albin
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Unread 04-18-2009, 02:36 PM   #11
opusgamma
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thank I found it... but had change it and it had less than 1000 miles... anything else?
http://autorepair.about.com/library/...s/bl860lib.htm
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