Could be a bad fuel injector too. Or a bad spark plug wire. I wouldn't think that a battery issue would cause this. I also wonder if this is related to carbon build-up. While I haven't heard of any issues related to severe carbon build-up on the 3.6L impalas yet (even with many more miles), I guess it could happen if the "conditions" were just right (tons of short trips, cheap gas, extended oil-change intervals, etc).

You said you replaced the spark plugs, but didn't mention the wires. If you didn't replace the wires, you might want to try that. If that doesn't help, I would either try to get a "top end cleaning" and maybe see if the injector can be tested.

There are no other codes other than the misfire code?

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Hi jtrosky,

Thanks for the reply. I should have mentioned that I swapped the spark plug wire with another cylinder when I thought I was swapping the ignition coil too. I assumed that it was all the same piece. I disconnected the wiring harness connection, removed the 10mm bolt, and pulled up the spark plug wire (with the ignition coil?). Swapping that didn't change the cylinder 6 misfire. Is it correct that the ignition coil is with the spark plug wire or is it somewhere else?

The only other code I get is a P0300 (random misfire). However, I only get that after I clear the P0306 code and it is only in the permanent codes on the scanner. It probably goes away when the vehicle goes through all it's tests. When I get the P0306 code back, the P0300 code is gone.

I don't think it makes a difference but I have used E85 fuel since it was new. The only time it had unleaded gas was when the dealer filled the tank when I bought it.

I have read on this forum that a failing battery has caused some crazy CEL problems. I figured it couldn't hurt, especially since the vehicle is almost 4 years old.

I'll look into the injectors next. Thanks for the suggestion.

 

Sorry - you are correct, I guess this engine really doesn't have the normal spark plug wires that I'm thinking of from older engines! Never really even though of that - sorry about the misinformation.

Although, maybe you moved some of the wiring when you swapped plug/coils, but there still has to be some other wiring involved that you didn't swap (or else the firing order would be messed up, right?). Maybe I'm not fully understanding exactly what you swapped - or I'm just not picturing how they're wired properly! I can't picture how the spark plug wiring is setup to be honest - will have to take a look at mine!

Right now, I'm leaning towards an injector issue. However, this car has a 100k mile powertrain warranty - I think I'd just take it to a dealership and let them figure it out! It's definitely power-train related if you are getting repeated, constant misfires that are setting a check-engine light like you are.

Have you considered taking it in for warranty coverage?

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Right now, I'm leaning towards an injector issue. However, this car has a 100k mile powertrain warranty - I think I'd just take it to a dealership and let them figure it out! It's definitely power-train related if you are getting repeated, constant misfires that are setting a check-engine light like you are.

Have you considered taking it in for warranty coverage?

Injectors, sensors, etc are excluded from that warranty. I had my hopes up until I just checked the warranty manual.

 

^+1. No plug wires with cop, lol.

 

Wow - that's messed up - they exclude everything that normally fails!!!

EDIT: But, it still may be worthwhile to take it to a dealership and pay the $79 "diagnostic" fee. That way, if it's not an injector and is something that is covered under warranty, you won't waste any more money replacing parts. Worst case, they'll tell you for sure that its an injector.

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save your money you cannot trust mechanic they will tell you anything to try to rob you of your change I recommend that you purchase the AL 539b OBD2 reader and diagnostic tool from autel they have online videos that tell you how to use it to do everything YouTube $89 and does absolutely everything you need to do as long as you are willing to learn a little bit It's a Wonderful Tool Man honestly it does everything that those $3,000 heavy duty diagnostic machine like the Vantage Pro by Snap-on trending all over the internet right now and by the way I'm having the exact same problem and I'm not sure exactly what's causing it but I know that my short-term fuel trim is reading 99% and now my long-term fuel trim is -10 on a different bank so I'm not sure if that means I have a vacuum leak somewhere or what but I am studying and learning and I need help I'm learning how to read the graph and the Freeze Frame data I keep popping a toad for absolute manifold pressure low voltage slow another one for voltage High another one for Cylinder 6 misfire another one for mass air flow bar metric pressure correlation circuit low

 

And, fwiw, good 'ol GM has recently reduced the 100k mi. powertrain warr. down to 60k mi. even though it doesn't apply to donzi's '13.

 

Is this a direct injection engine? If so may need to have the top end cleaned if carbon deposits building up on intake valves causing misfire.

 

Yes, I do believe it is a direct injection engine. One of the things I was concerned about is the problem with the valve coking I have read about on this forum.
http://www.impalaforums.com/8th-gen.../8th-gen-engine-performance/419481-2013-3-6l-with-1-300-miles-valve-coking.html

I never did install a catch can.

Update:

I took the vehicle to the dealership this afternoon. Preliminary findings from the mechanic revealed low compression (90 psi) in the #6 cylinder. I was told it should be 120 psi. The service advisor said that he was 95% sure that it would be covered under warranty but that they would need to pull the head tomorrow to see what was going on. I'm keeping my fingers and toes crossed that GM covers it. I've never had any problem with oil consumption and the oil changes have either been done by the dealership using their Dexos 1 synthetic blend or by me using Mobil 1 full synthetic. They did give me a Hertz 2015 Impala rental car to use in the meantime. Pretty sweet ride!

I'll update when I hear something. Thanks to all for your responses.

 

So they did a compression test ? But did they do a wet comp test?
Did they bring #6 to TDC and charge that cyl with air to see if it's on the intake or exhaust side?

Sounds to me like you may have a bad injector .. And that bad injector may have caused a lean condition in that cycilnder & possibly bent a valve ... Just a guess though

Or carbon build up & a valve isn't closing all the way

 

Donzi:

A lot of that stuff MAY be warrantied under the EMISSION warranty
which is usually longer than the powertrain warranty..............

Better to take it to the dealer and pay the diagnosis fee and a tech 2
hookup to pinpoint the problem and quit throwing parts at it and
PULLING your HAIR out !

 

I wonder if this wouldn't have happened if regular e10 was used instead of e85. If compression is that low it's either valve orhead gasket. A pretty severe misfire probably caused it initially, but why? I'm interested to know the outcome.

 

Update:
I finally got the vehicle back from the dealer yesterday. The mechanic started with replacing the exhaust valves in cylinders 4 & 6. Still leaked. The dealer then sent the head out for repair. Machine shop said the valve guides were toast. Dealer ordered a new head and installed. So far, so good. Covered by the GM 5 year/100,000 miles engine warranty. I hope using E85 exclusively didn't cause the issue. Unsure what caused the problem. Didn't install a catch can? Maybe. Also, oil never got low and was always changed near when the oil life monitor message came on. All I know, after all the past emission error codes, replacing parts the last 2 years (purge solenoid, purge canister, gas cap, gas pedal w/throttle sensor, etc) and now this last issue, there will be a 2013 Impala in a dealer's used car lot soon.

 

Wow! Who knew that something of this magnitude GM was able to cover. Would using PURE E85 all the time cause this issue? Why would anyone use it, if it would cause this type of headache? SMH, trying to save the Planet, yet wreaking the machines that one uses to commute.

 

Interesting... I will say that this is NOT a common issue with the 3.6l Impalas, so maybe there really is something with the E85 usage (very few people run E85 from what I've seen).

I'm really not sure what causes "valve guides" to fail. Could it be because oil change intervals were so long - most people recommend 5k mile oil change intervals at most and DIC oil life monitor can go up to as high as 10k miles between changes).

Just thinking out loud here... Anyone have any input as to what causes valve guides to fail like this?

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Interesting... I will say that this is NOT a common issue with the 3.6l Impalas, so maybe there really is something with the E85 usage (very few people run E85 from what I've seen).

I'm really not sure what causes "valve guides" to fail. Could it be because oil change intervals were so long - most people recommend 5k mile oil change intervals at most and DIC oil life monitor can go up to as high as 10k miles between changes).

Average interval between oil changes was approximately 7,300 miles. When the dealer did the oil changes, they used their synthetic blend. When I did them myself, I used Mobil 1 full synthetic.

I'm at a loss on what caused this issue. I wish the guy that started the valve coking thread would chime in with an opinion. I have been using E85 exclusively in my current and past GM vehicles for years. In fact, I don't even consider a new GM vehicle unless it is E85 compatible. I currently have a 2014 Equinox with 65,000+ miles, all with E85. I have yet to have a check engine light or any emission issues with the Equinox.

For now, I'm going to continue to use E85. I like that less of my money goes to the Middle East. I'm hoping this was just a one time anomaly.

 

Personally, I would change the oil more often. Even with full synthetic oil, most recommend 5k mile oil change intervals max. These DI engines are very hard on oil. I know that GM has recalibrated the DIC Oil Life Monitor systems multiple times now and personally, I still don't think they have it right. Goes too long between oil changes.

Now whether or not that actually has anything to do with your failure, I have no idea.

Do you do a lot of very short-trip driving?

From what I've seen, "valve coking" is not a major issue on these Impalas (haven't heard a single complaint from a single person yet). Even it you did have severe valve coking, not sure if that also affects the valve guides. And if you did have major valve coking issues, I think that the dealership would have also replaced the intake valves as well (or at least did a manual cleaning), but I didn't see anything about that in your update.

Do you know if the dealer ran into any severe valve coking on the intake valves during teardown? Again, I just haven't seen this be a real problem on the 2012+ Impalas.

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here is everything all data pro has on the code

DTC P0300-P0306

Diagnostic Instructions

Perform the Diagnostic System Check - Vehicle See: Testing and Inspection\Initial Inspection and Diagnostic Overview\Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
Review Strategy Based Diagnosis See: Testing and Inspection\Initial Inspection and Diagnostic Overview\Strategy Based Diagnosis for an overview of the diagnostic approach.
Diagnostic Procedure Instructions See: Testing and Inspection\Initial Inspection and Diagnostic Overview\Diagnostic Procedure Instructions provides an overview of each diagnostic category.
DTC Descriptors

DTC P0300
Engine Misfire Detected
DTC P0301
Cylinder 1 Misfire Detected
DTC P0302
Cylinder 2 Misfire Detected
DTC P0303
Cylinder 3 Misfire Detected
DTC P0304
Cylinder 4 Misfire Detected
DTC P0305
Cylinder 5 Misfire Detected
DTC P0306
Cylinder 6 Misfire Detected
Circuit/System Description

The engine control module (ECM) uses information from the crankshaft position sensor and the camshaft position sensors in order to determine when an engine misfire is occurring. By monitoring variations in the crankshaft rotation speed for each cylinder, the ECM detects individual misfire events. A misfire rate that is high enough can cause 3-way catalytic converter damage. The malfunction indicator lamp (MIL) flashes ON and OFF when the conditions for catalytic converter damage are present.

DTCs P0301 through P0306 correspond to cylinders 1 through 6. If the ECM is able to determine that a specific cylinder is misfiring, the DTC for that cylinder is set, and the corresponding fuel injector is disabled. To retest for a misfire, the ECM re-enables the fuel injector(s) after 4 crankshaft revolutions or after 8 crankshaft revolutions for manual transmission equipped vehicles. For catalyst damaging misfires the ECM re-enables the fuel injector(s) after a 30 second delay to retest for a misfire. This 30 second periodic re-enabling occurrs until the end of the drive cycle or until no further catalyst damaging misfire events are present.

Conditions for Running the DTC

DTC P0010, P0011, P0013, P0014, P0016, P0017, P0018, P0019, P0020, P0021, P0023, P0024, P0068, P00C8, P00C9, P0101, P0102, P0103, P0106, P0107, P0108, P0111, P0112, P0113, P0114, P0117, P0118, P0119, P0123, P0191, P0192, P0193, P0222, P0223, P0335, P0336, P0340, P0341, P0345, P0346, P0365, P0366, P0390, P0391, P0606, P0651, P16F3, P2101, P2135, P2227, P2228, P2229, or P2230 is not set.
The engine speed is between 350 and 7,000 RPM. OR
The engine speed is less than 1,000 RPM and DTC P0315 is set.
The engine coolant temperature (ECT) is between -7 and +127°C (19 and 261°F).
If the ECT is colder than -7°C (+19°F) at start-up, this diagnostic will not run until the ECT is between 21 and 127°C (69 and 261°F).
The ignition voltage is between 9-32 V.
The ECM is not detecting rough road.
The evaporative emissions (EVAP) leak detection is not active.
The ECM is not in fuel cut-off or decel fuel cut-off mode.
The fuel level is greater than 10 %.
Torque Converter Clutch (TCC) is not applied/active.
DTCs P0300 through P0306 run continuously when the above conditions exist for at least 1,000 engine revolutions.
DTCs P0300 through P0306 run continuously when the above conditions exist and the ECT is warmer than 47°C (117°F) for at least 1,000 engine revolutions for the first failure occurance, 200 engine revolutions after the fist failure occurance for catalyst damaging misfire(s).
Conditions for Setting the DTC

P0300

The ECM detects a crankshaft rotation speed variation indicating a misfire rate sufficient to cause emissions levels to exceed a predetermined value or a misfire rate high enough to cause catalyst damage.

P0301, P0302, P0303, P0304, P0305, P0306

The ECM detects a crankshaft rotation speed variation indicating a single cylinder misfire rate sufficient to cause emissions levels to exceed mandated standards.

Action Taken When the DTC Sets

DTCs P0300-P0306 are Type B DTCs.
The ECM may disable up to two fuel injectors of misfiring cylinders when a catalyst damaging level of misfire is present, and will flash the malfunction indicator lamp (MIL).
Conditions for Clearing the DTC

DTCs P0300-P0306 are Type B DTCs.

Diagnostic Aids

A misfire DTC could be caused by an excessive vibration from sources other than the engine. Inspect for the following possible sources:
A tire or wheel that is out of round or out of balance
Variable thickness brake rotors
An unbalanced drive shaft
Certain rough road conditions
Transmission operation
Broken or weak valve spring
Cracked Spark Plug Insulators
A damaged accessory drive component or belt; remove the belt and safely operate the engine to evaluate
High resistance in the circuits of the injectors may set a misfire DTC without setting an injector DTC. Test the injector circuits of the affected cylinder(s) for a high resistance if you suspect a condition.
If the condition is intermittent, observing the scan tool IC Circuit Test and Fuel Injector Circuit Test Status parameters may help isolate the condition. The circuit test status parameters will change from OK or Not Run to Fault/Malfunction if a condition exists.
A condition in the heated O2 sensor (HO2S) heater control circuits may set a DTC P0300.
Reference Information

Schematic Reference

Engine Controls Schematics See: Diagrams\Electrical\Powertrain Management\System Diagram

Connector End View Reference

Component Connector End Views See: Diagrams\Connector Views\Connector End Views By Name\AA - AU\A/C Compressor Clutch

Electrical Information Reference

Circuit Testing See: Testing and Inspection\Component Tests and General Diagnostics\General Electrical Diagnostic Procedures\Circuit Testing\Circuit Testing
Connector Repairs See: Testing and Inspection\Component Tests and General Diagnostics\General Electrical Diagnostic Procedures\Connector Repairs\Connector Repairs
Testing for Intermittent Conditions and Poor Connections See: Testing and Inspection\Component Tests and General Diagnostics\General Electrical Diagnostic Procedures\Circuit Testing\Testing for Intermittent Conditions and Poor Connections
Wiring Repairs See: Testing and Inspection\Component Tests and General Diagnostics\General Electrical Diagnostic Procedures\Wiring Repairs\Wiring Repairs
Powertrain Component Views See: Locations\Components\Powertrain Component Views\Left Front of Engine Components
DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions See: Diagnostic Trouble Code Descriptions\Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References See: Testing and Inspection\Programming and Relearning\Control Module References for scan tool information

Special Tools

J 26792 - HEI Spark Tester

For equivalent regional tools, refer to Special Tools (Diagnostic Tools) See: Powertrain Management\Computers and Control Systems\Tools and Equipment\Special Tools.

Circuit/System Verification

Engine idling at the normal operating temperature.
¤ If there is an abnormal engine noise, refer to Symptoms - Engine Mechanical See: Engine, Cooling and Exhaust\Engine\Testing and Inspection\Symptom Related Diagnostic Procedures\Symptoms - Engine Mechanical.
Verify that no other DTCs are set.
¤ If a DTC is set, refer to Diagnostic Trouble Code (DTC) List - Vehicle See: Diagnostic Trouble Code Descriptions\Diagnostic Trouble Code (DTC) List - Vehicle.
Observe the scan tool Cylinder 1-6 Current Misfire Counter parameters. The Current Misfire Counters should not be incrementing.
Engine idling, perform the Cylinder Power Balance test with a scan tool to isolate the misfiring cylinder. The engine speed should change when each injector is disabled.
Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
Circuit/System Testing

Verify that the following conditions do not exist:
Vacuum hose splits, kinks, and incorrect connections
Engine vacuum leaks
Crankcase ventilation system for vacuum leaks
Fuel pressure that is too low or too high-Refer to Fuel System Diagnosis See: Powertrain Management\Computers and Control Systems\Testing and Inspection\Component Tests and General Diagnostics\Fuel System Diagnosis.
Contaminated Fuel-Refer to Alcohol/Contaminants-in-Fuel Diagnosis See: Powertrain Management\Fuel Delivery and Air Induction\Fuel\Testing and Inspection.
Exhaust system restrictions
¤ If you find any of the above conditions, repair as necessary.
Ignition OFF, remove the T8 ignition coil of the misfiring cylinder, but leave the electrical connector connected.
Inspect the ignition coil boot for the following conditions:
Holes
Tears
Carbon tracking
Oil contamination
Water intrusion
¤ If you find any of the above conditions, repair as necessary.
Install the J 26792 - HEI spark tester to the boot of the appropriate T8 ignition coil and ground.
Note: An erratic or weak spark is considered a no spark condition.

Attempt to start the engine and observe the J 26792 - HEI spark tester. The spark tester should spark.
¤ If there is no spark, refer to Electronic Ignition System Diagnosis See: Powertrain Management\Computers and Control Systems\Testing and Inspection\Component Tests and General Diagnostics\Electronic Ignition (EI) System Diagnosis for diagnosis of the ignition coil.
Ignition OFF, remove the spark plug from the misfiring cylinder. Verify that the spark plug does not exhibit the following conditions:
Gas, coolant, or oil fouled-Refer to Spark Plug Inspection See: Engine, Cooling and Exhaust\Engine\Spark Plug\Testing and Inspection.
Cracked, worn, incorrectly gapped-Refer to Ignition System Specifications See: Powertrain Management\Ignition System\Specifications.
¤ If there is a condition with the spark plug, replace the spark plug.
Exchange the suspected spark plug with another cylinder that is operating correctly.
Engine idling, observe the scan tool Misfire Current Counter parameters. The misfire should not follow the spark plug exchange.
¤ If the misfire follows the spark plug, replace the spark plug.
If all conditions test normal, test or inspect for the following:
A lean or rich Q17 fuel injector-Refer to Fuel Injector Balance Test See: Powertrain Management\Computers and Control Systems\Testing and Inspection\Component Tests and General Diagnostics\Fuel Injector Balance Test.
An engine mechanical condition-Refer to Symptoms - Engine Mechanical See: Engine, Cooling and Exhaust\Engine\Testing and Inspection\Symptom Related Diagnostic Procedures\Symptoms - Engine Mechanical.
Repair Instructions

Spark Plug Replacement See: Engine, Cooling and Exhaust\Engine\Spark Plug\Service and Repair
Ignition Coil Replacement - Bank 1 See: Powertrain Management\Ignition System\Ignition Coil\Service and Repair\Ignition Coil Replacement - Bank 1
Ignition Coil Replacement - Bank 2 See: Powertrain Management\Ignition System\Ignition Coil\Service and Repair\Ignition Coil Replacement - Bank 2
Repair Verification

Perform the Diagnostic Repair Verification See: Verification Tests after completing the diagnostic procedure.
To verify that the performance of the catalytic converter has not been affected by the condition that set this DTC, perform the Repair Verification for DTC P0420 or P0430. Refer to DTC P0420 or P0430 See: P0420.
Clear the DTCs.
Turn OFF the ignition for 2 min.
If the repair was related to a DTC, duplicate the Conditions for Running the DTC and use the Freeze Frame/Failure Records, if applicable, in order to verify the DTC does not reset. If the DTC resets or another DTC is present, refer to Diagnostic Trouble Code (DTC) List - Vehicle See: Diagnostic Trouble Code Descriptions\Diagnostic Trouble Code (DTC) List - Vehicle the Diagnostic Trouble Code (DTC) List - Vehicle and perform the appropriate diagnostic procedure.
Engine idling, observe the Misfire Current Cyl. 1-6 parameters with a scan tool. The misfire counter parameters should not be incrementing.
¤ If the misfire counter parameters are incrementing, a misfire still exists.
To verify that the performance of the catalytic converter has not been affected by the condition that set this DTC, perform the Repair Verification for DTC P0420. Refer to Diagnostic Trouble Code (DTC) List - Vehicle See: Diagnostic Trouble Code Descriptions\Diagnostic Trouble Code (DTC) List - Vehicle.

 

Have you tried running a bore scope camera and seeing if there is any "gunk" built up on the valves? And if so, try running a cleaner. I recently used the CRC DI Cleaning spray, and the solution seemed to have silenced my car.

 

Does this engine have cylinder deactivation? I wonder if that could have contributed to the bad valve guides.

I've got a 2007 9C3 that has the deactivation and I worry about it. I normally run in 3rd unless I'm on the highway to prevent it from activating.

 

No, the 3.6l LFX engine does NOT have any type of cylinder deactivation...

Really strange - I honestly can't figure out what could have cause the valve guides to go "bad' so early in the engines life - unless it was just a manufacturing defect from the factory - but if that were the case, you'd think that you would have had issues way before 60k miles.

But I really don't know much about valve guides and what can cause them to go "bad", so I'm really not sure...

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I know in another thread, there was talks about installing an oil catch can, but I honestly thought that the oil vapor was needed to lubricate the throttle plate. Would excess oil cause sludge build and turn them "bad"?

 

Wanted to post as my sons 2012 Impala LT was doing the same exact thing in 2023. P0306 Check Engine, with Stabilitrak (sorry if not spelled right) error. We took it to a local mechanic and they said it was a major issue with the motor and needed the entire thing replaced. They even said the compression of cylinder 6 indicated a huge problem. Quoted $5k to $10k. Yea, no thanks. We did a lot of searching and this forum post popped up. We checked the plugs, all were fine and gap was perfect. Swapped Coil Packs, issue was same cylinder. Pulled valve cover to make sure it wasn't a broken valve spring which I saw in one youtube video. Wanted to rule out that possible issue. Last thing we did was pulled the fuel injectors. Little bit of work but not that hard. Tested all of them and guess what, number 6 was not functioning. All the rest did the battery click test (youtube video shows this). Pretty low tech but it seemed to prove that cylinder 6 was experiencing a problem.. yea, no fuel. We replaced the fuel injector, put it all back together and car runs perfectly. Spent $120 at Napa auto parts and felt good saving $4,880 or more.

Short version: Check your fuel injectors!

If you want to replace your injectors make sure you enter your VIN into this site GM parts site and find the real Fuel Injector part number for your vehicle. You can use the part number to cross reference with auto parts stores.

Video series regarding getting to the injectors : I cannot post links so search youtube for : GM 3.6 LFX V6 Fuel Injector Replacement by Certified Shadetree

I hope this many year after initial post update helps. This may not fix your problem, but at least try/check your injectors before replacing an entire engine.