Hey All,

[Please see truck specs in my signature]

Over past several months I've had my check engine light chime and flash a couple times while driving. The light will flash 3 or 4 times in sequence and then turn off and not happen again. This might happen once every 6 weeks (random intervals). I pulled the P0300 code one time, and most other times I would not even have a pending code by the time I connected my Hypertech tuner to read the DTCS. When this happened I did not hear or feel anything unusual from the engine, so I didn't let it bother me.

Last night while driving the check engine light blinked and flashed like described above except it happened about 4 times in the one 20 minute trip. My fuel light had just come on about 10km ago so I stopped at a gas station and filled up with 87 octane (tuner is set to same) hoping that this might solve the issue. I also made sure that I turned the gas cap about 3-4 clicks. On the 2km drive home from gas station the check engine light came on but instead of flashing it just remained on all the way home. When I got home I left the truck on, grabbed my tuner to pull the code(s) and again found P0300. I looked under the hood (briefly) and did not see anything that looked strange or unusual. This morning I started up the truck and the check engine light was still on, so now I am paying it a little more attention. Despite my hesitation to drive it, I was already late for work so I took the truck for my daily 9km commute. The drive in to work today felt pretty normal.

I need help figuring out what is wrong and what is needed to fix. I'll go over some of the work I've recently done (that might be relevant to this issue) as I'm sure this information would be helpful in diagnosing:

• The truck is at 191,000km and I replaced the spark plugs with NGK ZFR6F-11G (factory recommended plugs) at around 156,000km. At around 186,000km I took all coils and spark plugs out just so I could re-install with a little dab of diaelectric grease, thinking this might resolve the random misfires that I was experiencing. I also used an air compressor to blow out any contaminants from the spark well and wiped any dirt off the coils. I also moved some coils around to new cylinders thinking that if the issue was related to a coil, moving it might help identify it.
• I replaced the PCV valve at around 175,000km
• I replaced the waterpump, installed a 180 thermostat, and replaced the coolant at 186,000km
• At 170,000km I removed the throttle body to clean it out with throttle body cleaner. I used a new gasket to install. One mistake that I made is I misread 100 in-lbs as 100 ft-lbs and I overtorqued 2 of the 4 bolts that hold the throttle body to the intake manifold. The heads of the bolts snapped off but luckily the throttle body just has brass sleeves and the bolts only thread into the manifold. With 4 new dealership bolts I reinstalled the throttle body and properly torqued the bolts. I do not think that I cracked anything (but you never know)

I have a friend in the office who brought me his BlueDriver to borrow, it is an OBD2 diagnostic scan tool and gives me a little more information than the tuner does. I am curious if any information in the scanner's report is an indication of where the failure is occuring. Here is the code scan report:
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I also exported the freeze frame report, I believe this information reflects the values recorded by the PCM at the time of the code being set:
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Nov 02, 2017 10:31
Make: Dodge Year:2008
Trouble Code P0300 triggered Freeze Frame.
Code Def: Random/Multiple Cylinder Misfire Detected
PID : Description : Value
04 : Calculated Engine Load Value : 23.5 %
05 : Engine Coolant Temperature : 75 °C
06 : Short Term Fuel Trim Bank 1 : -7.8 %
07 : Long Term Fuel Trim Bank 1 : 13.3 %
08 : Short Term Fuel Trim Bank 2 : -3.9 %
09 : Long Term Fuel Trim Bank 2 : 11.7 %
0B : Intake Manifold Absolute Pressure : 25.0 kPa
0C : Engine RPM : 701 rpm
0D : Vehicle Speed : 77 km/h
0E : Timing Advance for #1 cylinder : 20.5 °
0F : Intake Air Temperature : 25 °C
11 : Absolute Throttle Position : 17.6 %
1F : Run Time Since Engine Start : 783 seconds
2C : Commanded EGR : 0.8 %
2D : EGR Error : 0.0 %
2E : Commanded Evaporative Purge : 53.7 %
2F : Fuel Level Input : 15.7 %
33 : Barometric Pressure : 99 kPa
42 : Control Module Voltage : 14.576 V
43 : Absolute Load Value : 18.8 %
44 : Commanded Equivalence Ratio : 0.999 λ
45 : Relative Throttle Position : 7.1 %
46 : Ambient Air Temperature : 6 °C
47 : Absolute Throttle Position B : 17.3 %
49 : Accelerator Pedal Position D : 15.7 %
4A : Accelerator Pedal Position E : 7.5 %
4C : Commanded Throttle Actuator : 7.1 %

The scan tool also lets me monitor different data sources live (fuel system status, engine coolant temp, mass airflow pressure, MAF rate, throttle position, etc) but I'll admit that I don't really know how I could use this information. Are there certain values that I could/should monitor to diagnose?

I have tried doing my share of research and I know the number of possible causes is pretty long. Shout out to jkeaton for this post:

Where do I begin? There are other posts floating around where guys have said they've replaced a ton of sensors, spark plugs, etc only to still have the problem. I don't want to approach this by just replacing everything, I figure I should systematically eliminate possible causes to find the root of the issue.

I know it is hard for anybody to hit the nail right on the head just based on the description I've given here. But any and all help or suggestions or comments that you guys have will be extremely helpful.

Thank you in advance!

 

I'd pull the plugs, inspect the plugs for fouling. Then do a compression test.

I've seen the misfire code on a Ford truck end up being a cracked insulator on a spark plug.

 

Thanks for the suggestion. I stopped off at a local parts store just before closing Friday night and I rented a compression pressure gauge. I’ll do the compression test tomorrow and report back. While working I will inspect all coils and verify plugs have correct gap. If gap is slightly too small or slightly too large can I push on the grounding electrode either inwards or outwards to correct gap? I don’t expect to see much fouling as plugs looked good about a couple months ago but I have a good feeling that this compression test will be the ticket. I will update my progress tomorrow.

Thanks again for your help!

 

If the electrodes aren't too worn, you can regap the plugs if they need it. If the electrode is all rounded off though, probably be better to just replace them.

 

Should I replace these? Picture of coils and spark plugs is exactly as they came out. Worst spark plug was chosen for close up pic.

Coils, and Spark plugs w/ 35,000km
Worst spark plug
Electrode closeup

 

Replace the plugs, put the coils and such back in. The electrodes are REALLY worn...... and may be the cause of your issue.

 

Thank you, going to store to get new plugs right now.

Okay compression test complete. All six cylinders achieved either 180 or 182 psi. Specification reads 170-225psi, so I sit a little low in the range, but still acceptable. I think what is more important is that there is even compression in all six cylinders.
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I guess I will have to get these new spark plugs in and then I'll see if the misfire code continue occuring. Hopefully this is the fix. I have diaelectric grease as well, should I use this when installing new plugs? Can anyone 'remind' me how and where to use the grease?

 

I just smear a bit around the aluminum contact part of the spark plug, and call it good. Of course, a little around the porcelain wouldn't hurt either, make the "wires" easier to take off next time.

 

Yeah, I ended up just putting a thin layer on the ceramic part of plug only and thing layer inside the coil boot.
Everything’s back together now. I disconnected battery to clear PCM and I cleared all codes. Hopefully this fixes my issues. Strange that previous spark plugs only got about 35,000km on em, I used NGKs specified plugs last time too.

I’ll report back if I continue seeing the same misfire problems again. Thanks all for the help!!

 

Let us know how it turns out.