The dreaded crank no spark.

[adairmowing]

2001 XJ with 170k so far. Jeep overheated recently from a blown power steering pulley and began overheating a few blocks from home. I rolled the dice and got it back to the house and replaced the PS and topped the radiator back off. Since the 17th it hast started and ran, it has had the crank no start issue. It initially showed p1391 I replaced the CPK, AND CPS sensor. I Have cleaned the throttle body as well. All the sensors read 5v keyed on with the exception of the coil pack which never reads over 0.19 when cranking. The plugs are not getting any spark and I now have both P0122 and p0123.

My question is partly what should the normal voltage leading to the coil pack be? And what other directions should I look? I'm leaning towards the ECU possibly being fried.

Any guidance or help would be immensely appreciated!

 

[Tim_MN]

ECU failure is very highly unlikely. Follow the OBD-II self-diagnostic trouble codes.

Suspect the TPS. Test the TPS.


A Jeeper had OBD-II Check Engine Light trouble codes P0123, 0122, and 0121, Installing a new genuine Jeep TPS sensor did not solve the codes or cure the symptoms. On the highway the driver noticed the cruise control didn’t work either, and the Jeep was sputtering/stalling, The turn signal was acting weird, sometimes it would turn on, sometimes not...sometimes it would blink 10 times a second like it had a bulb gone out. Others Cherokee owners report the odometer randomly goes blank. The cure to all the symptoms was a new clock spring.

COMPLAINT: TPS TROUBLE CODE WILL NOT CLEAR

A late model Jeep with a 2.5 or 4.0 liter engine and the AW4 transmission comes in with the “MIL” Check Engine Light illuminated and a complaint of late shifts. A scan reveals a code P0123, “TPS Voltage High”, is stored. The scan tools data list indicates that the TPS signal wire voltage is at 5.0 volts at closed throttle, and then ranges up to 11.5 volts. A back probe of the TPS signal wire (usually is an Orange/Dk Blue wire), shows 5.7 volts at closed throttle, with a similar rise in voltage as the throttle is opened. A check of the TPS 5 volt supply and ground circuit prove that both of these circuits are good.

A check of the TPS signal wire with the TPS disconnected shows the same 5.7 volts. Inspection of the wiring between the TPS and the PCM and TCM shows no faults. A replacement TPS does not cure the problem, neither does replacement of the PCM or TCM.

TESTING: Unplugging a faulty Clock Spring should return the TPS voltage to its’ normal readings. Or, you can remove the Horn fuse in your fuse block - this will remove the 12 VDC supply to the clock spring. Once the short circuit is temporarily disconnected, you should be able to reset the trouble code, and confirm you diagnosis of a faulty clock spring.

CAUSE: The Switch Sense circuit in the Clock spring in the steering wheel hub has shorted to battery voltage from the horn button circuit. When the Switch Sense Circuit shorts to the 12 volt HORN circuit the TPS signal voltage is driven high and remains there as shown. This is because the 5 volt reference voltage used by the Cruise Control “Switch Sense” circuit and the TPS are shared inside the PCM.

CORRECTION: Replace the Clock spring assembly. Once the Clock spring has been replaced be sure to check the sensor 5volt reference voltage at the PCM to insure that circuit has not been damaged by the short to power. Also check the TPS signal range to insure the TPS has not been damaged.

 

[adairmowing]

Went to re check the sensor wires this morning and the the power/right was 5V, the middle/ sensor was 4.74 and the ground was 0. Is the sensor wire high for being only keyed on?

 

[Tim_MN]

If the TPS tested correctly, solve for the P1391 code.


P1391 - Intermittent Loss of CMP or CKP Signal. Loss of the Cam Position Sensor or Crank Position Sensor signal has occurred.

P1391 JEEP Possible Causes
- Faulty Crankshaft Position Sensor (CKP)
- Crankshaft Position Sensor (CKP) wire harness is open or shorted
- Crankshaft Position Sensor (CKP) wire harness circuit poor electrical connection
- Faulty Camshaft Position (CMP) Sensor
- Camshaft Position (CMP) Sensor wire harness is open or shorted
- Camshaft Position (CMP) Sensor wire circuit poor electrical connection.

P1391 – Possible symptoms:
(1) Random misfire/stumble/bucking/stalling, often over bumps or right hand turns or when going into reverse.
(2) Shorted out the Fuel pump/ECU power wire.
(3) A improperly indexed distributor/cam sensor may exhibit surging, light bucking or intermittent engine misfiring. This will most likely occur when the vehicle is at operating temperature and under a light load at approximately 2,000 rpm. The proper indexing procedure must be used as outlined in the service manual.

Often replacing the faulty sensor fixes the P1391 code, but not necessarily. Therefore it's important to check the following:
• Check that the Cam and Crank sensor wiring isn't routed too close to sharp metal edges, or to hot exhaust parts.
• Visually inspect the wiring at the sensor for any burn marks, bare wires, or discoloration indicative of melting / chafing of insulation, and other damages.
• Visually inspect the cam sensor for damage. Make sure the magnet is firmly attached. The sensor can be tested.
• Visually inspect the reluctor wheel inside the distributor or Cam Sensor.
• Inspect the distributor assembly for excessive wear.
• If everything checks out okay, then test the Crankshaft Position Sensor.

If you buy any OBD-II engine sensors, make sure to buy genuine Jeep or NTK sensors.
Potential Fixes:
Fix #1:
Inspect your O2 wire harnesses for bent or pushed back wire plugs pins, damaged wires, chafed insulation, or failed wire splices. Use a volts/ohms multi-meter to check the resistance of the ground wire circuits from each sensor. Replace corroded ground wires/connectors and clean ground wire connection points.

Fix #2:
The timing may off. Re-index the distributor/cam sensor per the FSM instructions, or replace faulty distributor/cam sensor pickup module.

Read this article: Scan Tools, O-Scopes and Toothpicks here >> https://web.archive.org/web/20200820085756/http://jeep.blackonyx.net/pdfs/jcss.pdf

Read this thread >> https://www.jeepforum.com/forum/f19...352-p0353-crank-cam-sensor-issue-fix-3487474/

Testing the Throttle Position Sensor and Coolant Temperature Sensor is also recommended.