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Unread 02-13-2011, 01:40 AM   #1
RacerX
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XJ Crank Position Sensor

Quote:
Originally Posted by CJ7-Tim View Post
Troubleshoot and test, before you buy new parts.

The CPS is the most common failure, but not the only one that can cause a no-start.



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. Inspect/test/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.

.
- Anyone know the differences with testing a 1989 (RENIX) XJ

I noticed the plugs are different, now wonder if I'm testing wrong???

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Unread 02-13-2011, 07:27 AM   #2
cruiser54
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Testing procedure 87 - 90 is what you're looking for. There are only 2 wires in the plug.
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Unread 02-13-2011, 11:18 PM   #3
RacerX
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So just test the voltage between the 2 wires? Or ground to block?
For test 1 I got 200 Ohm
Test 2 I think I got 0.1v - if I did it right.
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Unread 02-14-2011, 04:59 AM   #4
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If you tested between the wires you should have .5 AC volts upon cranking.
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Unread 02-14-2011, 02:48 PM   #5
RacerX
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Ok - need a new one.
Thank you for the responses.
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Unread 03-15-2011, 10:11 PM   #6
dangerdakota
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My jeep sport 4.0l died well driving. found a broken o2 sensor, replaced but nothing... I am running on low funds but my truck has no spark in any cylinders.. I need advice on how to fix it.. I got a confusing obd2 codes p0101 to p0106.. which means all six injectors will not respound... what is wrong, i need help !!
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Unread 03-16-2011, 05:46 AM   #7
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Quote:
Originally Posted by dangerdakota View Post
My jeep sport 4.0l died well driving. found a broken o2 sensor, replaced but nothing... I am running on low funds but my truck has no spark in any cylinders.. I need advice on how to fix it.. I got a confusing obd2 codes p0101 to p0106.. which means all six injectors will not respound... what is wrong, i need help !!
Google your codes first and read up on them.
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Unread 03-30-2011, 05:40 PM   #8
RacerX
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Quote:
Originally Posted by cruiser54 View Post
Google your codes first and read up on them.
What codes?

ALSO - How the ---- do I get this out?
OR, what is the R&R procedure for this sensor?

I can't see how I can get a wrench down in there!
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Unread 03-30-2011, 05:58 PM   #9
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Quote:
Originally Posted by RacerX View Post
What codes?

ALSO - How the ---- do I get this out?
OR, what is the R&R procedure for this sensor?

I can't see how I can get a wrench down in there!
Sorry. I inadvertently responded to the hijacker's post.

Do it from underneath with a socket and long extension(s)..
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Unread 03-30-2011, 09:03 PM   #10
RacerX
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Oh .. ha!. ok, nevermind. (I should have read the quote)

Thanks if it stops raining tomorrow I'll clime under and try it.
Thanks.
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Unread 04-01-2011, 12:07 PM   #11
RacerX
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OK
I replaced the crank position sensor.
it didn't help - it starts, and as soon the initial hi idle comes down, it dies!
starts, dies....
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Unread 12-31-2011, 04:37 PM   #12
searlesy
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Hi Guys, first post here, I will head over and introduce myself shortly, and thought that I would just tag on the back of this thread. I recently had exactly the same problem, did the diagnostics and got battery disconnect, CAS sensor and O2 sensor.

I have just replaced the CAS according to the directions found (excellent indeed), and it sparked straight up. First drive was fine, no problems, but it now seems to have developed a problem again, where it looses all ignition momentarily, causing a miss whilst driving along. I would guess that this is related to the sensor, as I still get exactly the same codes when diagnosing.

I didnt disconnect the battery (just thought of this now), is this needed to "reset" the computer to make it work properly? I also noticed that I didnt see a rubber grommet as described above, although it may have been stuck to the bell housing.

Any ideas as to what might be going on?

Cheers,

Matt
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Unread 12-31-2011, 08:41 PM   #13
searlesy
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Small update, did a battery disconnect and the miss now seems to happen only at low rpm and disappears when you give it a bootfull.

Does this sound like I have a faulty crank sensor from new? Diagnostics have now cleared, all I have is battery disconnect and end of codes, which surprises me.
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