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Electrical:: Need Help from the Team

XJJeeper59

NAXJA Forum User
NAXJA Member
Location
San Diego
Electrical, Gas Issue, CPS???
Engine Stalls Dead on Road
99 XJ, 4.0.
160,000mi on body, Jasper Reman engine 3,000mi ago, Don't ask LOL. Sounded like a rod bearing. Can't remember if we swapped the CPS for New one, But pretty sure it was replaced
NOTEs:
* Not running Hot, under 210 full time..
* Issue Started while running washboard roads, aired down to 15psi. Rough road cobble sized rocks. But then continued on freeway
* XJ would give a Hic-Up "What the "F" was that?" or 2 before stalling
* XJ would just Shut Off (Stall), Tach dropped to Zero, Dead, Coast to a stop try to restart, crank, crank, crank, Nothing. Key out wait 1 to 2 min, Fired back up and idles fine.

***Just finished great trip through Death Valley mountains. Issue started yesterday. Got to end of trail (Downhill, 2nd Low) , Jeep stalled dead. Waited a min or 2 and it fired up. Drove back to camp, ran fine.
Today started fine, drove about 60 miles toward home, boom stalled again. Popped hood made sure wires secure and in place, nothing unusual, fired up. Drove 10mi same thing, made 3mi same thing, 1mi, 300ft same. I was 100mi from home had AAA tow (Covered me, Get AAA Extra). Any ideas where to Start looking for Issues? Thanks Folks...
 
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CPS would be a likely suspect.

CranKshaft Position Sensor (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 genuine Jeep 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.

Typical CPS Symptoms, (not all symptoms may be present, or occur at the same time) -
- Random stalling
- 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.
- Fuel pump should run and prime for 3-5 seconds.
- No spark at the spark plugs.

When the ignition key is first turned ON, 12 volts travels from the ignition switch to the ASD relay. The PCM provides ground to the ASD relay to energize it. The ASD relay sends the 12 volts to the primary side of the coil. If after a few seconds no signal is detected from the faulty CPS, the PCM opens the ASD relay and 12 volts power to the coil and fuel pump is removed.


If the CPS/CKP is failed sometimes the OBD-II 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 help 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 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 exhausts pipe. A short circuit from melted insulation or from broken O2 sensor wires can blow a fuse and the ECU/ECM will lose communication.
-Check the ground connection for the PCM. Make sure it is clean, snug, and has no corrosion.

If you buy a new CPS, get a genuine Jeep CPS. Most auto parts stores sell cheap crappy Chinese "Lifetime Warranty" parts that are poorly manufactured from inferior materials and are often out of specification, or even failed, right out of the box. The ones that aren’t faulty often have a short service life before they fail. Always buy top quality replacement parts and genuine Jeep sensors. Numerous threads detail long and frustrating searches for a "problem" that ended up being cured simply with genuine Jeep repair 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)



CPS Testing
TESTING PROCEDURE 1991 –2001 4.0L H.O. engines
1. Near the rear of fuel rail, disconnect sensor pigtail harness connector from main wiring harness.
2. Place an ohmmeter across terminals B and C or 2 and 3 (See Image). 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.
 
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