No Start im assuming its the Crank Position Sensor - JeepForum.com
 
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post #1 of 9 Old 06-24-2009, 09:19 AM Thread Starter
Fiend101
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No Start im assuming its the Crank Position Sensor

So I came home from work yesterday and the jeep was running fine. I went to go out and it wouldnt start. Seemed like it wasnt getting fuel because it would crank but wouldnt start. I have pressure at the rail so its not a fuel problem. I tested for spark and I dont have any. So im assuming its the Crank Posion sensor but could it just be the ignition coil? Is there a way to test that would rule one or the other out? 96 4.0 auto 2wd. Oh and I also tried it in Neutral so its not the NSS. Thanks


2000 TJ what I should have started with
1996 2wd XJ DD waiting for 4x4 conversion (Totalled, not by me)
1991 2 door XJ waiting to be parted or repaired(sold) Bought it back. Gotta love a 2 door (Sold)
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post #2 of 9 Old 06-24-2009, 09:27 AM
LeftOfCenterXJ
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CJ7-Tim has a great write up on testing the CPS:

Quote:
Originally Posted by CJ7-Tim
The most likely cause of it cranks and cranks but won't start up is the Crankshaft Position Sensor (CPS) located on the transmission bell housing. Often this part is also referred to as the CranKshaft Position Sensor (CKP) CPS/CKP failure is very common. The CPS/CKP can stop working with no warning or symptoms and the engine will not run or the engine may randomly stall for no apparent reason.

Crank Position Sensors can have intermittent “thermal failure”. This means that the CPS/CKP fails when engine gets hot, but works again when it cools back down.


Symptoms –
- Starter cranks and cranks but engine won't start up
- Fuel gauge and voltage gauges may not work or display properly.
- You sometimes will have No Bus on the odometer after 30-60 seconds.
- A failed CPS/CPK may or may not throw a CEL trouble code.
- No spark at the spark plugs.
- Fuel pump will run and prime for 3-5 seconds.

If the CPS/CPK is failed sometimes the OBDII code reader cannot make a connection to the computer or cannot read Check Engine Light/MIL codes because the CPS/CPK has failed.


Diagnostic steps to confirm the CPS is the cause of your no-start


You should be able to verify a bad cps, by unplugging it, and turning the ignition key to on. If the voltage gauge and/or the fuel gauge now displays correctly, replace the CPS.

Unplugging and reconnecting the CPS sensor where it connect to the main harness near the back of the intake manifold usually resets the ECU and if the jeep fires right up after doing this you can bet that the CPS is the culprit and needs to be replaced.

Exchange the fuel pump relay and the ASD relay with one of the other similar ones in the PDC to eliminate the relays as the cause of the no-start Confirm that the fuel pump to runs for 3-5 seconds when you turn the ignition key to ON.

Eliminate the NSS as a cause of no start. Wiggle the shift lever at the same time you try to start. Put the transmission in Neutral and do the same. Do the reverse lights come on when the shifter is in Reverse?

Inspect the wires and wire connectors at the O2 sensors on the exhausts pipe. A short circuit from melted insulation or from broken O2 sensor wires can blow a fuse and the ECU/ECM will loose communication.

Begin with basic trouble shooting of the start and charge systems. Remove, clean, and firmly reconnect all the wires and cables to the battery, starter, and alternator. Look for corroded or damaged cables and replace as needed. Do the same for the grounding wires from the battery and engine to the Cherokee's frame/body. Jeeps do not tolerate low voltage or poor grounds and the ECM/ECU will behave oddly until you remedy this.

CPS Testing


Crankshaft Position Sensor Connector (CPS/CPK)





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 (See Image). 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.

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.

.

"Too weird to live, too rare to die"
2000 XJ Silver, 3", 31's DD
88 XJ Blue, 4.5", 33's, Project
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Quote:
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post #3 of 9 Old 06-24-2009, 10:12 AM
Jon00XJ
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yup sounds like your CPS has went kaput.

But I may be wrong but if your not getting fire on a 95 you may need to check your distributor and im not sure if you have a camshaft sensor or not but ou could check that too. Mine has that distributor less ignition system so I may be wrong.
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post #4 of 9 Old 06-24-2009, 01:09 PM Thread Starter
Fiend101
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Swapped it out and it fired right up. It was one of the easier fixes Ive done on the jeep too. I expecting it to be much worse since all the threads said it was a pita to change

2000 TJ what I should have started with
1996 2wd XJ DD waiting for 4x4 conversion (Totalled, not by me)
1991 2 door XJ waiting to be parted or repaired(sold) Bought it back. Gotta love a 2 door (Sold)
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post #5 of 9 Old 06-24-2009, 01:47 PM
LeftOfCenterXJ
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glad to hear your XJ is alive again

"Too weird to live, too rare to die"
2000 XJ Silver, 3", 31's DD
88 XJ Blue, 4.5", 33's, Project
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Quote:
Originally Posted by Juju
It makes your trolling more credible to be grammatically correct. Lets everyone know you're a legitimate troll, not just one of those poser trolls.
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post #6 of 9 Old 06-24-2009, 01:56 PM Thread Starter
Fiend101
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I was stupidly happy. About half the time when something is replaced something else went bad at the same time so I was overjoyed when it started

2000 TJ what I should have started with
1996 2wd XJ DD waiting for 4x4 conversion (Totalled, not by me)
1991 2 door XJ waiting to be parted or repaired(sold) Bought it back. Gotta love a 2 door (Sold)
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post #7 of 9 Old 06-24-2009, 05:14 PM
xjfever
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If it was an easy swap for you , you must have long skinny arms

  1. '95 XJ country edition, 4" coils/3/4" spacers, HD leafs with extra main added in, Ironman adjustable control arms, rough country shackles, aussie locker, JK rubicon shocks, 35" mudder's, soft 8's, cobra cb
  2. Sold'99 WJ limited, 4.7L, 3" IRO lift. Bilstein shocks, JK rubicon wheels, 255/70/17's, carolina driveshaft, IRO adjustable control arms, IRO adjustable A-arm
  3. Sold '00 TJ, 4" lift, rusty's adjustable control arms, skyjacker shocks, rock krawler adj. trac-bar,rugged ridge SYE and RE driveshaft, soft 8's, 35" mud king xt's,XJ HP D30 w/aussie locker, 4:88 yukon gears, hella 500's, rock crusher diff covers
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post #8 of 9 Old 06-25-2009, 01:43 PM
dmm219
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Quote:
Originally Posted by Fiend101 View Post
Swapped it out and it fired right up. It was one of the easier fixes Ive done on the jeep too. I expecting it to be much worse since all the threads said it was a pita to change
you may be thinking of the ZJ...replacing the CPS on that is a total PITA. Its not too bad on an XJ...
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post #9 of 9 Old 06-26-2009, 07:06 AM Thread Starter
Fiend101
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Quote:
you may be thinking of the ZJ...replacing the CPS on that is a total PITA. Its not too bad on an XJ...
No I havent been on the ZJ side of the forum in months since my ZJ decided to die.

2000 TJ what I should have started with
1996 2wd XJ DD waiting for 4x4 conversion (Totalled, not by me)
1991 2 door XJ waiting to be parted or repaired(sold) Bought it back. Gotta love a 2 door (Sold)
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