99 Cherokee XJ 4.0L Having a Snit - JeepForum.com
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post #1 of 10 Old 06-30-2020, 12:18 AM Thread Starter
HikerJeep
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99 Cherokee XJ 4.0L Having a Snit

During the past month or so, there have been about a half-dozen instances while driving that my Jeepster has a momentary (under two seconds) "cut-out" (I'd call it a hiccup) when the motor stops running and then immediately continues on as if nothing happened; if cruise control is on, it does not interrupt that; if the nightime lights are on, they are not affected; once or twice the cut-out has happened as I was in 1st or 2nd gear, starting up a hill; yesterday it was while on cruise at about 65/70 mph out in the middle of Eastern Oregon's wide-open freeways; my mechanic says he can only guess unless he can actually have the computer connection active at the instant it happens. My sense (fear?) is that if the instant suddenly was extended it would be the end of the motor which would be quite disappointing since Im at 337,000 miles (original motor & transmission).


Any thoughts?


Much appreciated.

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post #2 of 10 Old 06-30-2020, 07:30 AM
jtec
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when it acts up -
tell about radio - stops playing then continues same channel? All memory still there?
The lights, Do the stay on or flash off then back on?
the cruse control- did it have to be reset?

With a scanner you could look at the emission monitors have been reset to 'not ready' ?

Anything elec added to jeep- POS remote start? anything plugged in DLC? Kill switch? anything added?

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #3 of 10 Old 06-30-2020, 08:07 AM
CJ7-Tim
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The most common and most likely suspect for random unexplained stalling is the Crankshaft Position Sensor. The CPS can and should be tested.

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 CPS lifespan is about 150-200,000 miles.

Crank Position Sensors can have intermittent “thermal failure”. This means that the CPS/CKP fails when the 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 NoBus displayed on the odometer after 30-60 seconds.
- A failed CPS/CKP may or may not throw a CEL trouble code.
- No spark at the sparkplugs.
- 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 computer or cannot read Check Engine Light/MIL codes because the CPS/CKP 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.
- Check the orange wire going to the CPS or cam position sensor for 5 volts with the key in the run position. A partial short in a sensor can cause the input voltage to the CPS (or most sensors) to be low and can trigger a no-start or no bus situation.
- 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 these relays as the cause of the no-start. Confirm that the fuel pump 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 exhaust pipe. A short circuit from melted insulation or from broken O2 sensor wires can blow a fuse and the ECU/ECM will lose communication.

If you buy a new CPS, get a genuine Jeep CPS. Cheap crappy “Lifetime Warranty” parts are often out of specification or even failed right out of the box. They usually also have a shorter service life than better quality parts. Buy good quality repair parts and genuine Jeep sensors for best results.

You must also perform 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.

Crankshaft Position Sensor Connector(CPS/CKP)


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CPS Testing


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 or 2 and 3 (See Images). Ohmmeter should be set to the 10K-or-2OK scale for this test.
3. The meter reading should be open (infinite resistance). Replace sensor if a low resistance is indicated.

TESTING PROCEDURE for 1987–1990 4.0 L engines
Test # 1 - Get a volt/ohmmeter 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 .5 VAC, replace it.

The 2000 and 2001 will have the CPS in the same location on the bell housing, but the wire connector is on the passenger side, near or on top of the Transfer case, not as shown in the diagram below. Simply follow the wire from the sensor to the wire connector.
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post #4 of 10 Old 06-30-2020, 03:34 PM
JWELK
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Follow CJ7-Tim's advice and change the Crank sensor. While you're at it, purchase a Cam sensor. Both are subject to thermal failure (did it overheat on you?) and they have similar life expectancies. I've never gotten 150K out of mine, let alone 200. I've found the OEM's to be no more reliable than the after market. But that is me. The Cam sensor is easy to replace. It is under the distributor cap. And can be done with a phillips screwdriver and flashlight if need be. Neither will throw a code, as the engine must be running to create a code.
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post #5 of 10 Old 07-01-2020, 10:42 AM Thread Starter
HikerJeep
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Thank you to each! Will follow-up and see where it goes. Much appreciated.
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post #6 of 10 Old 07-02-2020, 11:00 AM
jim9006
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I had something like that happen on my '99. I ran with it doing that all summer until it got to the point where it was happening all the time. Turned out be the TPS. No codes were recorded.
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post #7 of 10 Old 07-06-2020, 11:11 PM Thread Starter
HikerJeep
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jtec -

You asked:
when it acts up -
tell about radio - stops playing then continues same channel? All memory still there?
The lights, Do the stay on or flash off then back on?
the cruse control- did it have to be reset?

Radio / lights / cruise - nothing is affected; keeps working as they should.
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post #8 of 10 Old 07-07-2020, 03:04 AM
rep-tile
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These are signs of bad CPS. Strongly suggest an OEM brand sensor. Check also the main engine ground from the negative battery to the engine block. Sometimes it can get loose or corroded. The engine block provides in turn a ground to the spark plugs and possibly some sensors or accessories that might not have a dedicated ground wire.

Your fear is very much unfounded. Intermittent cut offs are rarely a sign of mechanical failure.

04 WJ 4.0 - Avital 4103, DB-ALL
91 XJ 4.0 - Avital 4103, Stage-2 aFe intake system, BBK high flow Throttle Body, 703s injectors, Jones Exhaust A3518M-5
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post #9 of 10 Old 07-09-2020, 10:43 PM
ski4by
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Hiker Jeep. I would start out with a careful inspection of the wiring and connections. Check to make sure all grounds are secure and free from corrosion. Manipulate connectors carefully with the engine running and see if you can duplicated the condition. You may very well have an intermittent component but eliminating a faulty connection is always a good place to start before replacing a component. you may even try gently tapping sensors and connections to check for an indication.

Dave D.
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post #10 of 10 Old 07-10-2020, 03:25 PM Thread Starter
HikerJeep
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Again, thanks to y'all for your information and taking time to help on this. Much appreciated.

I replaced the TPS and, thus far, there has been no hiccup -- so I'll run this way for a while and see if the issue has gone away. Am also going to pass along your different comments to my mechanic and see what he thinks may need to be done further. Obviously, the mileage certainly requires "on-going care" of the rig of the sort y'all have suggested.

Again, thank you!
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