I have a 15 Jk with the 3.6 and it has a cylinder 3 miss fire. I replaced the plug, coil, injector, and manifold gaskets. I took it to a shop and they said I had low compression at idle and a fluttering vacuum. So they said I needed a head the valve seat was bad. They called today after doing the head and are saying it needs an engine it wasn't the head it has bad piston rings. Now this jk has 43,000 miles on it has never consumed oil and before and after the head has good cranking compression. Has anyone heard of a 3.6 needing piston rings?

Thanks all!

 

Welcome to JKF. Good group here, much knowledge, & friendly .. I have not read or heard of a 3.6L experiencing Ring issues; not saying it isn't possible .. ASK the shop for the compression test results,, dry and wet.. What work above what you posted have you had done in regards to the mis fire.. Check out this on Utube: 3.6 pentastar misfire AND ..

 

I did the plug coil and injectors for the miss. The shop said the dry compression was perfect. I will have to have them run a wet test and see. I think it's strange that it's had head symptoms and they changed it and are now saying rings and it doesn't have any symptom of that.
I have done a lot of reading on here before I had an account and saw all the knowledge and knew I had to ask!
thanks for your help!

 

Yadzz.. in my experience the DRY compression vs Wet .. if the Dry is perfect the WET will be same or higher. I'm not buying the "Rings" diagnosis.. Are you in Delaware County?

 

A "misfire" code doesn't necessarily mean the cylinder has not fired. Anything that slows the crankshaft when the computer expects to see it maintain or increase speed will throw the code.
There are many mechanical possible causes. Misfire has a very long list if things to check before parts are ordered.

P0300-P0306 CYLINDER MISFIRE

When Monitored:

Any time the engine is running, and the adaptive numerator has been successfully updated.

Set Condition:

The threshold to set the fault is application specific; it is tied to the level of misfire that will cause emissions to increase to 1.5 times the standard or in some cases 1%. It is always a two trip fault above the calibrated RPM. It takes 1 soft fail to set a malfunction and two trips to set the MIL. Three good trips to turn off the MIL.

Possible Causes
ASD OUTPUT CIRCUIT

INJECTOR CONTROL CIRCUIT

IGNITION WIRE

SPARK PLUG

IGNITION COIL

FUEL PUMP INLET STRAINER PLUGGED

RESTRICTED FUEL SUPPLY LINE

FUEL PUMP MODULE

FUEL PRESSURE LEAK DOWN

FUEL INJECTOR

ENGINE MECHANICAL

POWERTRAIN CONTROL MODULE (PCM)

VISUAL INSPECTION

NOTE: Anything that affects the speed of the crankshaft can cause a misfire DTC.

NOTE: When a Misfire is detected for a particular cylinder, the PCM will shut down that cylinder's Injector Control circuit.

Turn the ignition off.

- Visually inspect the engine for any of the following conditions.

- Worn serpentine belt

- Binding Engine-Driven accessories: A/C Compressor, P/S Pump, Water pump.

- Misalignment of the Water pump, P/S Pump and A/C Compressor pulleys

- Corroded PCM power and ground circuits.

- Improper CKP, CMP, MAP, and TP Sensor mounting

- Poor connector/terminal to component connection. i.e., CKP sensor, Fuel Injector, Ignition coil, etc.

- Vacuum leaks

- Restricted Air Induction system or Exhaust system.

- Internal engine component failures.

SPARK PLUG

Turn the ignition off.

Remove the Spark Plug.

Inspect the Spark Plug for the following conditions.

- Cracks

- Carbon Tracking

- Foreign Material

- Gap size out of specifications

- Loose or broken electrode

NOTE: Lightly tap the bottom of the spark plug on a solid surface. The electrode in the spark plug should not move.

ENGINE MECHANICAL

Check for any of the following conditions/mechanical problems.

ENGINE VACUUM - must be at least 13 inches in neutral

ENGINE VALVE TIMING - must be within specifications

ENGINE COMPRESSION - must be within specifications

ENGINE EXHAUST SYSTEM - must be free of any restrictions or leaks.

ENGINE PCV SYSTEM - must flow freely

TORQUE CONVERTER STALL SPEED - must be within specifications

POWER BRAKE BOOSTER - no internal vacuum leaks

FUEL - must be free of contamination

CAM LOBES - must not be worn excessively

CYLINDER LEAKAGE TEST - must be within specifications

VALVE SPRINGS - cannot be weak or broken

POWERTRAIN CONTROL MODULE (PCM)

Using the wiring diagram/schematic as a guide, inspect the wiring and connectors between the related Sensor, Coil, Injector, and the Powertrain Control Module (PCM).

Look for any chafed, pierced, pinched, or partially broken wires.

Look for broken, bent, pushed out or corroded terminals. Verify that there is good pin to terminal contact in the related Sensors, Coils, Injectors, and the Powertrain Control Module connectors.

Refer to any Technical Service Bulletins that may apply.

 

Yeah id be very skeptical of a bad rings diagnosis without the accompanying oil burn. I have replaced the engine on my 13 and prior to that i had a warranty head replacement done. There was all sorts of oil burn and bullshit pointing to bad rings. I heard so much bullshit come out of dealers mouths in the 4 months it was being worked on. Being that they just changed the head, maybe it's something simple like a misseated gasket or over torqued and cracked manifold causing a leak in #3. Good luck with the hunt.

 

Talked to the shop today and the said they reused the cams and rockers. They inspected them and the cams and rockers seemed fine... I'll be picking it up this weekend and checking it out on my own to see what I can see.

 

So after I checked it out. I pulled codes that were in there since shop and had p2302 and p2308 and also p0172. I disconnected the battery and clear codes that way drove it around and had no misfires but now have the p0172 code only. Bank 1 is running at about -28% while idling gets better when accelerating and decelerating. So maybe vacuum leak or o2 sensor is what I am thinking.