1997 4.0L Sputters and really rough idle - Jeep Wrangler Forum

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Old 05-17-2017, 10:22 AM
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1997 4.0L Sputters and really rough idle

1997 Wrangler 4.0 Sport Automatic. Changed Distributor and Crankshaft Position Sensor about 3 weeks ago due to hard starting issue. Jeep ran great for a few weeks, not when it gets to operating temps, it sputters out rpms drop to almost nothing then it comes back and repeats the issue over again. I have check ed fuel pressure and it stays at 49 psi even when engine sputtering out. So I think I can rule out fuel issues, Also changed Crankshaft Position Sensor again, Changed the Throttle Position Sensor and also unplugged o2 Sensor to rule that out. Does anyone have any suggestions to try I am at my wits end here. I have heard it could be a corroded wire or vacuum leak but I do not see anything out of the ordinary. The thing runs great until it gets up to operating temps then immediately sputters out. CEL codes are P0123 P0123 code definition

Throttle Pedal Position Sensor/Switch (TPS) A Circuit High Input

What the P0123 code means

P0123 is the generic OBD-II code which indicates that the Engine Control Module (ECM) has seen the TPS circuit A output voltage go above the sensor's expected voltage specification range.

What causes the P0123 code?

The TPS sensor circuit A range output to the ECM went above the specified voltage of 4.54 volts for more than 2 seconds, indicating a short in the sensor or wiring.
AND
P1391 - P1391 DODGE - CMP or CKP Signal Intermittent Condition 1 | Add Comment Possible causes Faulty Crankshaft Position Sensor (CKP) Crankshaft Position Sensor (CKP) harness is open or shorted Crankshaft Position Sensor (CKP) circuit poor electrical connection Timing belt or chain stretched or jumped Faulty Camshaft Position (CMP) Sensor Camshaft Position (CMP) Sensor harness is open or shorted Camshaft Position (CMP) Sensor circuit poor electrical connection. What does this mean? Possible symptoms Engine Light ON (or Service Engine Soon Warning Light) Lack/Loss of Power The engine may be harder to start The engine may stumble or stall P1391 DODGE Description The Engine Control Module (ECM) detected the actual Camshaft Position Sensor (CMP) position disagreed with the expected CMP level.

Read more: https://www.autocodes.com/p1391_dodge.html
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Old 05-17-2017, 07:17 PM
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Updates...anyone please share any information

Current condition, starts up and idles normally, it will even drive normally until engine reaches 190 degrees (normal operating temps) then stalls, drops rpm, sputters out and eventually dies. It will easily restart after it dies but immediately starts dropping rpm’s and sputtering out until it dies.
Symptoms only occur after the jeep warms up to normal operating temps of 190 degrees.
Changed the Throttle Position Sensor, Crankshaft Position Sensor a second time, checked fuel pressure to rule out fuel pump or filter and all normal at 49 psi at all times, even while jeep was hesitating, sputtering and surging, the gauge remained at the normal 49 psi.
Swapped the ignition coil and the jeep idled normally and thought the issue was resolved however after some time the issue cropped back up, but the new coil definitely seemed to help the issue, the sputtering out and stalling was not bear as bad.

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Old 05-18-2017, 10:46 AM   #3
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I am not sure if simply unplugging the o2 sensor is a valid test. The o2 sensor should switch between .1 and .8volts. Measuring rise time with propane is a good test to condemn the o2. That will tell if the o2 is slow/lazy. With your tps code you should check reference voltage, ground, signal voltage. Sounds like you may have a connector /ground problem.
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Old 05-18-2017, 11:34 AM
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Thank you so as of right now the only code being thrown out is the p1391 - the intermittent signal from CMP or CKP, I have checked the wiring harness, cleaned plugs, cleaned connections at ECM, moved and jiggled wiring harness and wires near ecm and fuse box under hood to see if a short or bad connection would make it drop power but nothing. I will check this again and double check the grounds as well. Thank you for the suggestions, really appreciate it as I am running out of options and really want to try and fix this myself if at all possible. I have researched a ton and am keeping a list of what I have done and some diary notes as I am seeing a lot of other people with similar issues.
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Old 05-18-2017, 12:09 PM   #5
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What brand of CAM and CPS sensor did you use? TJs are picky when it comes to sensors and mopar brand is your best bet. I am leaning towards CAM with the issues you describe.
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Old 05-18-2017, 12:29 PM
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Thank you, the more I research the more I hear about the off brand (autozone) sensors, which I am using unfortunately. I guess I will change the Cam and Crank Sensors with Mopar and see if that cures it. Thanks everyone and I will document and keep this going for anyone else with similar issues.
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Old 05-19-2017, 02:25 PM
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Changed Oxygen Sensor (Upstream) cleaned up all grounds and checked wiring, now idles fine but will die when coming to a stop. Read something about Vehicle Speed Sensor? Any Thoughts on this guys?
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Old 05-19-2017, 02:43 PM   #8
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Are you loosing any antifreeze?
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Old 05-19-2017, 10:22 PM   #9
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Only if you are throwing a code for the speedo housing not connected.

Are you still throwing a CPS/CAM code? Cycle the key on/off/on/off/on and list the codes spit out on the odometer. Dont replace a bunch of random parts.
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Old 05-19-2017, 11:45 PM   #10
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I had that same problem on my '02 TJ and I changed out all the plug wired. On was folded/bent/pinched.

Ran well after that.

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