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01 XJ sport crank but no fire?

Iceman09

NAXJA Forum User
Location
OHIO
bought a 2001 xj for a project to turn into a DD. been working on it for a few days now to get it ready to see if it will start. went to go start it with the Gray key and it will crank and turn over but will not start. after about 30 seconds of cranking the "NO BUS" comes on with the motor light. however, the yellow "no key" light is on and wont start. is there any way to get around this issue? by disconecting the SKIM and putting a non SKIM ecu in? or am i going to have to spend a bunch more money to haul it to a dealer and have them re program the ecu? looking for the cheapest/fastest route on this, thanks.

Also, i have a 96 xj, could i swap that ecu into the 2001 to get it to fire? as long as i disconnect the SKIM module under the steering wheel? or will that kill my ecu?

or do i have other problems keeping it from starting? like the CPS
 
I think you’ve got a couple issues going on

No start sounds like the cps

The no bus issue is a connection issue on the cluster. Pretty common on the 01. Take the cluster out and clean the connections.
 
A no-bus combined with a no-start is most often and most likely a faulty CPS. A no-bus when the engine start/runs normally is a cluster issue.

Failure of the SKIM anti-theft system is somewhat common, and the simple solution is to remove the key reader device and then install a non-SKIM enabled ECU/PCM. SKIM failure would result in the engine starting and running for 3-5 seconds, and then shutting off.


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 the 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 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. 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 and/or the No-Bus is gone, 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. 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.

CPS Testing

Crankshaft Position Sensor Connector (CPS/CKP)
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standard.jpg

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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.


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.

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standard.jpg
 
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Im pretty sure you hit the nail on the head with this one. all the symptoms you have listed is exactly what i have including the code reader not being able to connect to the computer after multiple attempts, looks like ill be ordering a new CPS and ECU asap just so i can get rid of the SKIM nightmare.... Thanks for all the info, i appreciate it. hopefully ill have this jeep on the road soon!
 
Tim gives some of the best advice on our Cherokees based on experience and technical reference. When he replies, you can bet he's spot on. We are blessed to have you Tim. :sunshine:
 
Well, I tried disconnecting the CPS and still nothing. Still couldn't get the code reader to connect, and the no bus came back up. I'm quickly losing my patience on this project.... on a side note, I saw you mention something on this about checking the alternator. The previous owner used this as a parts jeep and took the alternator out of it. Would that make a difference as to why it's not starting? Would that cause an open circut to keep from firing? I plan on putting that back into it but I don't want to waste money on parts if I can't get this to fire.
 
Also, I did test the sensor with the ohmmeter and couldn't get anything to show up on it. Tested it on the harness side and it showed high resistance. And I tried wiggling the shifter while trying to start and that did not work either and no my back up lights did not work, however I'm not sure their are good bulbs in the lights, if any. I did pull off the gauge cluster and the connections were clean with no corrosion.
 
I listed most of the common faults. The CPS test for an OBD-II Cherokee is looking for no resistance/infinite resistance, which sometimes is displayed as OC for open circuit. Any 5 volt OBD-II sensor that is shorted out, or any wiring faults or short circuit causing 12 volts to cross to the 5 volts OBD sensor CCD Bus circuit can cause the ECM/PCU to stop functioning, or even fail. One at a time, disconnect each of the engine sensors and attempt to establish communications using the code reader after each sensor is disconnected. Not having an alternator installed is probably not good, besides a used alternator from the junkyard is not that much.
 
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