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Unread 10-29-2009, 06:03 AM   #1
sskinner
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Crank position sensor problems (maybe)

So last night after work go to start the jeep and she just cranks and cranks but will not fire. OK great so pop the hood looking for a possible loose anything electrical. Everything is tight and where its sopposed to be. I turn the key over and I hear the fuel pump prime then stop still no start. So I have someone else give it a try and there is a faint burnt eleltrical smell but no smoke and I was unable to see/tell where it was coming from. Everything that I have read and searched for points to the CPS but I have not read on how to test it. I know its testable with a omh meter (which I have) but I am not firmiluar enoughwith it to know where to set it. I found he pins I need to test I just am not sure what settings on the meter to select. Any help would be awesome. (and pics showing the setting would be even better)

thanks in advance

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Unread 10-29-2009, 07:17 AM   #2
xjryder
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the crank position sensor located on the bell housing on the driver's side, 2) 11mm bolts and a 3 wire plug located on the driverside next to the fuel rail (close to the firewall) I had the same problem, it was apparent when it started really hard, then died and then cranked over and over. also clean all sensors on the throttlebody I cleaned them and changed the CPS started right up
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Unread 10-29-2009, 10:29 AM   #3
CJ7-Tim
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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 (and will test as “good”) when it cools back down.

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 starter to engine block, and from the battery and engine to the Jeep's frame/body. Jeeps do not tolerate low voltage or poor grounds and the ECM/ECU may behave oddly until you remedy this.



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

If the CPS/CKP is failed sometimes the OBD-II trouble code reader cannot make a connection to the ECU/computer or cannot read Check Engine Light/MIL codes because the CPS/CKP has failed. Disconnect the code reader, disconnect the CPS/CKP wire connector, and reconnect the code reader. If the code reader establishes contact with the ECU and scans, your CPS/CKP is failed and needs to be replaced.


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 faulty 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. Don’t get tunnel vision and assume the sensor is bad (unless it tests bad with a meter). Damaged wiring or a dirty connector can inhibit the signal from making it to the computer. Check/clean/repair wiring or connectors as necessary.


CPS Testing


Crankshaft Position Sensor Connector (CPS/CKP)



.


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.


The 2000 and 2001 will have the CPS in the same location on the bell housing, but the wire connector may be on the passenger side, not as shown in the diagram below. Simply follow the wire from the sensor to the connector.

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Last edited by CJ7-Tim; 05-15-2010 at 08:03 PM..
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Unread 10-29-2009, 10:57 AM   #4
sskinner
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thanks for the info guys. Tim I saw your post elsewhere and was able to test it today with a multi meter when I got to work. is stuck in a closed position so when I get off work will have it towed home.
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Unread 10-30-2009, 01:05 PM   #5
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Well I got the damn thing out. ended up dropping the front driveshaft for easier access. once that was out it took me maybe 20 minutes to get it out. Just waiting on the part tomorrow to throw it back in.
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Unread 07-15-2010, 08:29 PM   #6
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thanks for the info tim
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Unread 08-04-2011, 07:46 PM   #7
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i got a 96 jeep cherokee sport it will run for a half hour then stops just like running out of qas try to start it back up just truns over will not start can anyone help
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Unread 08-04-2011, 08:07 PM   #8
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Quote:
Originally Posted by kid16823 View Post
i got a 96 jeep cherokee sport it will run for a half hour then stops just like running out of qas try to start it back up just truns over will not start can anyone help
When it happens, test the CPS as recommended in Tim's post above.
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Unread 08-07-2011, 10:53 PM   #9
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Thanks for the test procedure!
Very nice.

I had this happen, ...again!
However, this time after buying a new crank sensor, I tried to start it 1 last time, and it STARTED RIGHT UP!

So now I have an extra CPS (from Schuck's-O'Briens, whatever..?) still have the receipt, maybe I'll try taking it back in the AM.
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Unread 08-15-2011, 05:15 AM   #10
kid16823
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what would make my 96 jeep cherokee 4.0 shut down going down the road it run good sitting its like running out of gas i put a new cps in could it be in the timming or fuel pump and i did a tune up
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Unread 08-15-2011, 05:45 AM   #11
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Timing is not adjustable. A bad fuel pump COULD be causing your problem. You would need to test the fuel pressure to be sure. You can rent a fuel pressure gauge at many parts stores.

PS: Could you do us old guys a favor and use Capital letters to start sentences and periods or question marks at the end of those sentences, please?
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Unread 08-15-2011, 07:44 AM   #12
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Apparently the CPS does not fail gracefully. Is it worth having one on the shelf or with our Jeeps getting old just replace it after 12 years?
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Unread 08-15-2011, 10:26 AM   #13
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I firmly believe in Preventative Maintenance, as in replacing parts before they fail. All Jeep 4.0L will need a new CPS or two. I carry a spare CPS in all my Cherokees. Typical lifespan of a JEEP CPS is 125,000-175,000 miles. Cheapo "Lifetime Warranty" replacements from Advance/IdiotZone/PepBoys will have a shorter lifespan.
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Unread 08-15-2011, 06:55 PM   #14
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I agree with you Tim, I see CPS's on ebay for $45 they claim are OEM replacements. Where do you buy yours?
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Unread 08-15-2011, 10:12 PM   #15
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Quote:
Originally Posted by reran View Post
Where do you buy yours?
From one of the on-line Jeep Parts Departments. Some of the Dealerships do Internet parts sales. 30% off the retail price for Genuine Jeep parts.
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