Intermittent misfiring

[spoon359]

I have intermittent misfiring in one cylinder on my 3.6l engine. My mechanic has Changed O2 sensors, coil pack, plug and injector. He now thinks maybe it’s something electrical. Any ideas or suggestions would be appreciated

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[alphawolff]

What do you mean by intermittent misfire? Does the misfire happen after the vehicle sits overnight and then clears up after a few seconds? Does it happen while flooring it on the highway? Etc etc

 

[58Willys]

Pull the codes, go from there.

 

[spoon359]

What do you mean by intermittent misfire? Does the misfire happen after the vehicle sits overnight and then clears up after a few seconds? Does it happen while flooring it on the highway? Etc etc

By intermittent I mean it just does it at random. There is no pattern to it. Doesn’t matter if engine is hot or cold, flooring it or just cruising along. The start/stop light on dash comes on and immediately the cel light comes on and starts misfiring. I’ve by passed aux. battery and it hasn’t helped either. The randomness is why mechanic can’t seem to figure it out. Any ideas would be helpful.

 

[spoon359]

Pull the codes, go from there.

Mechanic pulled codes. Thats why he changed coil pack, plugs and injector but issue and codes keep returning.

 

[58Willys]

Do you know what codes?

 

[spoon359]

Do you know what codes?

I don’t know code numbers. I do know was codes for O2 sensors, coil pack/plugs and misfires. All on same cylinder

 

[Yawnie'sPapa]

I’ve by passed aux. battery and it hasn’t helped either.

That's never going to help any running issue, let alone a misfire. But my understanding from Jeep owners is that the aux battery does cause global warming. (at least that's the lore out there along with all of the other stuff it supposedly does)

Mechanic pulled codes. Thats why he changed coil pack, plugs and injector but issue and codes keep returning.

If he did a full diagnoses, including grabbing a freeze frame, he'd know if it was ignition or fuel. Chances are he only saw a code saying something like P0301 for example, which is a #1 cylinder misfire, but says little else.
"your mechanic" -is he trained with Jeep, or even modern vehicles specifically, or does he just look at codes and toss in any part that could be related?
Is "your mechanic" a Jeep dealer mechanic, or someone at a shop used to changing parts based on a code?

I'm wondering because even the software I have will tell me if it's an ignition related misfire, etc. - and a good troubleshooter will diagnose using deeper digs to check the voltage of the O2 sensors, catch a freeze frame and look at a whole set of criteria.

They can even scope the ignition system, monitor O2 sensor operation as it runs and do other deeper digs and troubleshooting.

This is one way I found the misfire on my wife's 2021 was ignition -

Error code: P0303
Cylinder 3 ignition failures
Test not complete
Error intermittent
Error warning lamp not requested
CARB Freeze Frame:
___________________
Fault code: P0303
PCM Mileage since MIL On: 0.00 miles
PCM Odometer: 950.27 miles
Open Loop - Bank 1: No
Closed Loop - Bank 1: Yes
Open Loop due to Driving Conditions - Bank 1: No
Open Loop with DTC - Bank 1: No
Closed Loop with DTC - Bank 1: No
Open Loop - Bank 2: No
Closed Loop - Bank 2: No
Open Loop due to Driving Conditions - Bank 2: No
Open Loop with DTC - Bank 2: No
Closed Loop with DTC - Bank 2: No
Engine load: 30.20 %
Freeze Frame Engine Coolant Temp: 66.00 Deg.C
Intake Air Temperature: 215.00 Deg.C
Ambient Air Temperature: 12.00 Deg.C
Short Term Fuel Trim - Bank 1: 12.49 %
Long Term Fuel Trim - Bank 1: -3.13 %
Short Term Fuel Trim - Bank 2: 9.37 %
Long Term Fuel Trim - Bank 2: -7.04 %
MAP Voltage: 1.96 V
MAP: 46 kPa
Atmospheric pressure: 97 kPa
Engine RPM: 875.00 rpm
Vehicle speed: 0 MPH
Throttle Position Sensor 1 Percent: 12.94 %
Battery voltage: 14.58 V
Fuel level: 95.69 %
Purge Solenoid Current: 0.00 mA
Purge Duty Cycle: 0.00 %
Idle Air Control (IAC) Current: 0.00 mA
Idle Air Control (IAC) Duty Cycle: 0.00 %
EGR Flow: 0.00 g/s
Current Adaptive Cell ID: 24
Spark advance: -2.00 Deg
AC Clutch: Disengaged
EGR Gassed Flowing: No
Power Steering High Pressure: No
AC Switch: Off
PRNDL in Gear: No
Brake switch: PressedLow Ethanol PWR Enrich Flag: No
Low Ethanol Therm Management Flag: No
Ethanol Gas For Sure: No
Ethanol Mode: No
Ethanol - 0% Blend Direction: No
Ethanol - 85% Blend Direction: No
Ethanol - Open Loop Fuelling: No
Ethanol Fine Tune Complete Previous: No
Ethanol Fuel Volume Changed: No
Ethanol Low Fuel: No
Ethanol Trigger On Fuel Volume Fault: No
Ethanol Trigger During Learn: No
Ethanol Learn: Disabled
Ethanol Course Update Ready to Learn: No
Ethanol Course Update: Not completed
Ethanol Fine Tune: Not completed
Actual Torque: 0.84 Nm
Potential Torque: 78.16 Nm
Target throttle position: 2.56 V
Electronic Throttle Control (ETC) Motor Directional Duty Cycle: -20.67 %DC
Electronic Throttle Control (ETC) Motor Duty Cycle: 20.67 %DC
Throttle position sensor 1: 2.58 V
Throttle position sensor 2: 17.42 V
Accelerator pedal sensor 10.44 V
Accelerator pedal sensor 20.22 V
Accelerator pedal position: 0.00 %
Brake switch 1: Released
Brake switch 2: Released
H-Bridge Circuit: Enabled
Ignition Run/Start Switch: On
Throttle Flow Adaptive: 0.13 g/s
Throttle Flow Multiplicative Adaptive: 2.00
PHI Adaptation Value: 0.00
Calculated MAP: 46.59 kPa
Ethanol Percent: 0.00 %
Turbo Boost Timer: 0.00 ms
Throttle Inlet Pressure: 0.00 kPa
Throttle Inlet Pressure Voltage: 320.34 V
Turbo Airport Mass Flow: 3.45 g/s
Turbo PRatio: 1.00
Turbo Torque Count: 0
Turbo Speed: 65535 rpm
Turbo Wastegate Duty Cycle: 200.01 %DC
Time since Run/Start: 45 sec
___________________

 

[alphawolff]

I don’t know code numbers. I do know was codes for O2 sensors, coil pack/plugs and misfires. All on same cylinder

Suggest taking it to a dealer. That's a lot of parts for a misfire. Coil plug & injector can be swapped with different cylinders to rule them out without outright replacing them. Seems proper diagnostic procedure isn't being followed here.

This really isn't a problem we can help you diagnose over the forum if you aren't the actual person working on the vehicle. Not even knowing which cylinder (or cylinders) is misfiring doesn't help either.

 

[spoon359]

Turns out it was another o2 sensor causing issue. Got it back from shop this afternoon. Thanks for everyone’s time.

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