[mikemaj82]

Every few months I seem to get a P0306 cylinder misfire code while driving. When I get home, I'll reset the code with my XTool D7, and it won't come back for a while. It seems to be in 2-3 month intervals. I don't feel any vibrating or hear anything different when the code is active, and the idle is normal. Just wondering why this would happen randomly. If it were a true misfire, the code should come right back after the reset and starting the engine again. If it happens again, I'm going to swap the coil with the one next to it, and see what happens. The car only has around 49K miles, and the spark plugs were changed about 2 years ago, and I put in Accel coils about 3 years ago. The only other thing I could think of is a possible issue with the injector or the wiring harness in that area being pinched.

 

[200_S_AWD]

Fault codes can be intermittent. It would be easier to find if the condition were all the time. It may take 2 occurrences of P0306 to mature into an 'active' fault code & turn on the 'ck eng' light. Before that, or as a 'one-trip' failure, it may show up as a 'pending' code.

The PCM is pretty accurate about misfire faults & I'm pretty confident that it is real. The PCM can detect misfires that we can't by measuring slight changes in crankshaft speed. The crankshaft is constantly slowing down on a compression stroke & speeding up on a power stroke. It looks for that. We even out the inertia & momentum pulses with a flywheel, but they are still there.

Spark plugs can tell a story. The tip of the #6 spark plug may look different than the other five. A whiter porcelain tip may indicate a 'lean' condition. Any carbon or soot may indicate a 'rich' condition for that cylinder. Due to how intermittent this is, you may see nothing out of the ordinary.

If the XTool D7 can read stored 'freeze frame' data, copy down what the PCM sees when the misfire occurs. Is it a miss at idle or at speed? Is it during acceleration or at a cruise? Warm or cold? etc.
What conditions are present when the misfire occurs may help us to find it. See what the freeze frames have in common.
Has the top of the motor ever been apart? It is important to secure the coil/injector wiring harness so it won't wear through & short when reassembling.

Swapping the #6 plug & coil with an adjacent cylinder is a good idea. See if the fault follows the plug/coil. Look for any faint arc streaks on the porcelain body.

 

[mikemaj82]

Thanks. I'm probably gonna just start with a coil. The code hasn't come back since this post.

 

[200_S_AWD]

Swap the #6 & #4 plug coils to see if the fault moves with the coil?

 

[mikemaj82]

Yea if the code comes back one more time that's what I'm gonna do.

 

[ChryslerCares]

Every few months I seem to get a P0306 cylinder misfire code while driving. When I get home, I'll reset the code with my XTool D7, and it won't come back for a while. It seems to be in 2-3 month intervals. I don't feel any vibrating or hear anything different when the code is active, and the idle is normal. Just wondering why this would happen randomly. If it were a true misfire, the code should come right back after the reset and starting the engine again. If it happens again, I'm going to swap the coil with the one next to it, and see what happens. The car only has around 49K miles, and the spark plugs were changed about 2 years ago, and I put in Accel coils about 3 years ago. The only other thing I could think of is a possible issue with the injector or the wiring harness in that area being pinched.

Hi there, @mikemaj82!

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Chrysler Cares

 

[mikemaj82]

It just came back today. Apparently, there is a surefire way to get it to come on. If the car is not yet at operating temperature, and I give it heavy gas from a stop, it will come on immediately. Happened twice like that now. If the car is already warmed up, giving it heavy gas will not cause a CEL.

 

[200_S_AWD]

This is good information to know. Not 'stone cold', but maybe 100℉ - 150℉ (37℃ - 65℃)?
Are these the correct OEM spark plugs?

 

[mikemaj82]

This is good information to know. Not 'stone cold', but maybe 100℉ - 150℉ (37℃ - 65℃)?
Are these the correct OEM spark plugs?

So apparently this one was a false alarm. By the time I was able to plug in my scan tool, the code had disappeared, but what was stored in the history was P0523 Oil Pressure Sensor Circuit High. This is another code that I get intermittently...every 3-4 weeks or so, on hard acceleration. The switch was on an aftermarket oil filter adapter housing that I got on Amazon, but I did save the old sensor so if it gets to the point where it becomes a permanent issue, I'll just swap in the OEM sensor.

But to answer your question, the spark plugs were replaced about 5,000 miles ago with Champion plugs...same ones that I pulled out. And I am the original owner so that's what was in there from the factory. And yea the temperature was probably closer to the lower range you posted.

 

[200_S_AWD]

It should store misfire codes along with the P0523 code.
The 'circuit high' fault is usually caused by an open circuit, like the sensor was unplugged with the ign on 'run'? Conversely, a 'circuit low' fault is usually caused by a short-to-ground.
Maybe travel around with the scan tool plugged in? Does it record 'live' data?

 

[mikemaj82]

Yes I can record live data with it. I'll see what I can get.