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Old August 24th, 2014, 13:02
NAXJA Forum User
Join Date: Aug 2014
Location: Boise, ID USA
Posts: 12
97 XJ won't start ...---...!

Newbie XJ owner stumped.
1997 XJ 4x4 Auto, 4.0 I-6. Nicely modified.

She has run like a champ up to now. Loaded up to go camping one Saturday. Moved it around in the driveway for loading. Started up and was running fine for engine warm up. All set to head for the hills. Turned engine off to unlock jockey box. Tried to restart, engine turns over strong but won't start. Good thing it happened in the driveway.

Battery strong - Optima Marine.
Replaced Plugs, Cap & Rotor.
Getting Spark from all six cleaned and inspected cables.

Fuel Pump kicks on w/ Key On.
Fuel Rail at 45 PSI w/ Key On.
TPS confirmed working.

No Engine Codes recorded.

Neutral Safety Switch allows engine to turn over in P & N.

All Fuses Good and Relays appear working.
Swapped Auto Shutdown Relay with Cooling Fan relay. No change.

At this point I have spark and fuel pressure.
Don't know how to confirm Injectors are providing fuel.
Ignition Switch? Maybe.

CPS has been changed out once.

Any bright ideas much appreciated.
Baronski of Boise.
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Old August 24th, 2014, 15:45
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98NWCherokee 98NWCherokee is offline
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Location: Portland, OR
Posts: 446
Re: 97 XJ won't start ...---...!

You mentioned your XJ is modified. Any chance you have an aftermarket alarm? I know you say your battery is good, but how do you know? Jeeps do not tolerate low voltage. Have you load tested the battery to see if it's good? How are your connections and grounds? You certainly sound like you know your way around a diagnostic process, but the simple things can always get us.

Last edited by 98NWCherokee; August 24th, 2014 at 16:16.
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Old August 24th, 2014, 16:52
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Tim_MN Tim_MN is offline
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Location: Minneapolis, MN
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Re: 97 XJ won't start ...---...!

Typically the CPS. It should be tested.

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 when it cools back down.
- 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 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.
-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.
-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.

If you buy a new CPS, get a genuine Jeep CPS, or the premium one from NAPA. 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)

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 (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.

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 .5vac, 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.

Originally Posted by bimmerjeeper

Go ahead and slam the liftgate down on a blanket, and see how long you are laughing.
Originally Posted by soyjer

Tim MAY be 100% correct, but why would a person automatically pick him as the expert .....
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Old August 25th, 2014, 16:14
NAXJA Forum User
Join Date: Aug 2014
Location: Boise, ID USA
Posts: 12
Re: 97 XJ won't start ...---...!

I'll check the CPS and confirm as it has been highly recommended.
Even though it's been changed recently, seems these are gremlins.

New to the XJ and MPI systems so appreciate the replies.

Also have an '82 CJ-7, 258 w/ Weber.
Mostly stock except for T-18 and Upgraded 300.
Lot's of OJT prior to Jeeps with various muscle cars.

Well back on my head.
Let ya know.
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Old August 25th, 2014, 17:27
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birchlakeXJ birchlakeXJ is offline
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Location: Melrose, MN
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Re: 97 XJ won't start ...---...!

What is the "quality of spark"? Very important. You are looking for a strong, BLUE, snapping spark.

Yellow/orange/white spark indicates a weak spark which may be caused by your ignition coil. Your coil can easily be tested for both primary and secondary resistances with a meter and a manual.

You can test if your fuel injectors are firing with a "noid light".

Good luck and keep us updated!
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Old August 25th, 2014, 17:42
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winterbeater winterbeater is offline
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Location: Royal Oak, Michigan
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Re: 97 XJ won't start ...---...!

Originally Posted by Tim_MN View Post
Typically the CPS. It should be tested.
Your write up is the best for testing the CPS. I'll certainly use it if I have issues.

I just wonder (and please correct me if I'm wrong), but could you have a good spark and still have a CPS that is preventing starting?

I'd try spray start at this point.

Last edited by winterbeater; August 25th, 2014 at 17:46.
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Old June 8th, 2019, 08:09
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Join Date: Aug 2014
Location: Boise, ID USA
Posts: 12
Re: 97 XJ won't start ...---...!

Always hate when nobody follows up on there posts. Practice what you preach. This was indeed the CPS. As a result, I keep a spare in my jockey box.
This little SOB will leave you stranded anywhere.
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Old June 8th, 2019, 15:28
denverd1 denverd1 is offline
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Location: Tyler, TX
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97 XJ won't start ...---...!

Damn right it will. My 2nd went out after trailering it 5 hours to Hidden Falls. Impeccable timing

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Old June 8th, 2019, 16:29
trust96xj trust96xj is offline
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Location: redlands
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97 XJ won't start ...---...!

That’s one thing I don’t miss about my xj is the damn CPS going out left and right.
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Old June 10th, 2019, 05:38
asymptonic asymptonic is offline
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Join Date: Jul 2012
Location: Austin, Texas
Posts: 250
Re: 97 XJ won't start ...---...!

Yep, stranded me in Big Bend. Now I carry a spare. I haven't had to replace #2 yet though. How many feet of socket extension do I need to get at it on trail?
1998 4.0 I6, AX15, NP231
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