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Unread 12-13-2011, 01:19 PM   #1
Tristan96
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Cherokee stalling while driving. Help Please.

I have a 96 Jeep Cherokee 4.0L and it has been acting up on me lately. I have done various maintenance things to her in the past two months, Alternator, Starter, Battery, Ignition Switch, Spark plugs all because she wouldn't start and some just needed to be new parts. I thought it was the NSS but one morning the problem was gone after starting it in neutral for a week. Yesterday and today the Jeep died after driving for about 5-10 minutes. It wasn't while idling but while driving. I pulled over and had a heck of a time trying to get her started again. Once started it ran without problems for the rest of the day, starting and driving like normal. I have looked online a lot for the possible problem. Can you tell me if it is the fuel pump, Crank Position Sensor, Throttle Position Sensor or maybe a combination or am I off track?

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Unread 12-13-2011, 01:28 PM   #2
CJ7-Tim
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All of those parts can be tested for proper function, search JeepForum or use the Google for test procedures. Test them one at a time until you determine the cause. The most common cause of stalling/hard starting similar to what you describe if the CPS.






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.

Typical 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.

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 or connectors 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. You must remove, scrape, and clean until shiny, the cable/wire ends, and whatever they bolt to. Jeeps do not tolerate low voltage, bad connections, or poor grounds and the ECM/ECU may behave oddly until you remedy this.

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. Check the ASD relay fuse.

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.



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.

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



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


1) 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 display correctly and/or the No-Bus is gone, replace the CPS.

2) If the CEL does not come on when the key is turned to the RUN position... then the CPS/CKP is bad.



3) 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.

The 2000 and 2001 will have the CPS in the same location on the bell housing, but the wire connector is near the Transfer Case, not as shown in the diagram below. Simply follow the wire from the sensor to the connector.



CPS Testing


Crankshaft Position Sensor Connector (CPS/CKP)



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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.


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Unread 12-13-2011, 11:28 PM   #3
Reptile
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It's more likely either a fuel issue or the CPS, or both which is possible but very unlikely. Problem is you are dealing with an intermittent issue so the best window of opportunity to successfully troubleshoot will be while you are having the issue... If the problem is with the fuel pump, your fuel pressure won't be within specs, if it's the CPS you will have no spark. I'm thinking the CPS here.
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Unread 12-14-2011, 03:30 AM   #4
tjwalker
It's the crank sensor!
 
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I'll jump on the crankshaft position sensor bandwagon here.

They often are intermittent before they fail catastrophically. Which means don't wait long on addressing this one.

If you have an old crank sensor, (do you know how many miles on yours?) I'd seriously consider replacing it with one purchased directly from Jeep for best reliability and longevity. Aftermarket crank sensors are "hit and miss" with a lot of miss. Plenty of threads with reliability problems with some (not all) aftermarket crank sensors.

I am NOT a fan of throwing parts at a problem, but a suspected intermittent problem with these symptoms, replacing the crank sensor is not a bad idea.......The crank sensor is the #1 sensor failure on the Jeep 4.0 engine.
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Unread 12-14-2011, 07:45 AM   #5
Tristan96
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My Jeep has 207,000 miles on it. Last night I cleaned every plug, connector, and ground I could find. I went and bought a crank position sensor $64.00 and got as far as getting the old one off and then checked to see if connectors were the same. Of course they weren't so back on went the old sensor. I know better than that but I was on a mission in the dark to get this fixed. I will keep y'all posted with my progress. Thank you for your feedback.

Tristan
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Unread 12-15-2011, 07:04 AM   #6
CRider74
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Question...is this one from Quadratec - http://www.quadratec.com/products/55125_04.htm the same as the one directly from Jeep? tjwalker mentioned above that this one should be bought directly from Jeep, hence my question...plus, why not an aftermarket one?
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Unread 12-15-2011, 07:26 AM   #7
seu83
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Quote:
Originally Posted by CRider74 View Post
Question...is this one from Quadratec - http://www.quadratec.com/products/55125_04.htm the same as the one directly from Jeep? tjwalker mentioned above that this one should be bought directly from Jeep, hence my question...plus, why not an aftermarket one?
I can't really say if the sensor from quadratec is mopar or not. I've never ordered from them before. The reason you want a mopar sensor though is because Jeeps are very picky about sensors and the cheap ones from autozone or advanced don't spec out the same. This isn't the easiest sensor to get to on the jeep so I'd get the mopar one from the dealer and call it a day. At least then you don't have to second guess the sensor later on.
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Unread 12-15-2011, 07:29 AM   #8
CRider74
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Appreciate the quick answer. After I posted that question, I called the local Jeep dealer...their price is $73 (compared to the $99 at Quadratec), so I guess if I find I have to replace it, that makes the decision even easier. Thanks again!
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Unread 12-15-2011, 07:53 AM   #9
xjstump
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My 99 xj did the same thing you discibed and I changed the crank senser and it fixed the problem, I got senser at NAPA and it worked just fine. I changed the senser about 3 years ago , so see you can getafter maket that will work.
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Unread 12-15-2011, 07:56 AM   #10
tjwalker
It's the crank sensor!
 
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Not all aftermarket crank sensors are flaky, but some definitely are.

And considering that the crank sensor is the most critical sensor on the vehicle and can leave you stranded and isn't much fun trying to replace on the side of the road or on the trail, my thought is why take the risk? Jeep sensors have known reliability.
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