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Discussion Starter #1
From 'Googling', I see these 3 spark plugs recommended most for my 2015 Accord SE I4-MT. I have an intermittent misfire again on cylinder #4 (P0304) but, I'm questioning blindly replacing the coil again after 20K~30K additional miles which are now at ~85K. The fuel injection system was professionally cleaned at ~65K miles so, I'm thinking a fuel injector issue is unlikely.

I likely have either another bad coil or some other 'wiring' issue or, the spark plug itself is becoming marginal. At ~85K miles it is time for new plugs anyway so, that took me down that rabbit hole!

Is there anything to suggest one of these spark plugs or a different model is better or significantly cheaper with essentially the same performance and longevity? The misfire sometimes is completely gone and sometimes is present. It generally is more prevalent when cold but, also occurs after getting fully warmed up. It will 'skip' occasionally or continuously cut out at ~3200RPM like a LIMP Mode is kicking in. With this intermittent nature of the miss, I am a bit puzzled as to the true cause and source of the issue. This takes me to coil-on-plug #4 again with new spark plugs.

With spark plug installation, do I need to do anything special like anti-seize on the plug threads or something else? It looks like torque is generally recommended at 11-14ft/lbs so, anything else to be aware of or consider?

I'm open to other possible causes and things to look at but, spark plugs seem reasonable at this point so I'm starting there with almost anything else I do. What am I possibly overlooking with this intermittent misfire?

Thanks!
Sid
 

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NGK was oem or Denso would be the best. Honda's don't run as good on the Bosch plugs. @ your mileage you may want to have the carbon cleaned out in the top end, try to use tier-1 gas. How did they clean the injectors ? Coils don't usually go bad, I have only had to replace 1 in 490K miles. Check your air intake hose for any cracks or leaks (may have to remove it). Look for a code & by online with pick up in the store (Advanced Auto). Amazon, E-bay have a lot of china counterfeits.
 

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Discussion Starter #4
The fuel injector cleaner was one of those compressed tanks that tied into the fuel rail with an additive to the gas tank. I generally run fuel from high volume stations so, fuel quality is generally pretty high.

For cleaning the carbon on the top end, are you suggesting some sort of aerosol spray in the air intake?

Prior to this, the car was a very strong runner with great power so, I'm doubting a fuel injector issue. However, having two coil on plugs go bad on the same cylinder is suspicious which is why I'm hesitating to blindly change just this one component at this point.

The only code I have is the P0304 which is Cylinder 4 misfire.

Regarding plugs, I've used Bosch in the past with really good results but, things do change over time. Denso and NGK are well respected brands so all three appear to be very similar in terms of construction to quality which is why I down selected to those three.
 

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A compression check could be revealing. That would be my next step.
 
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Discussion Starter #6
A compression check could be revealing. That would be my next step.
If compression was down, why would it be an intermittent misfire? Bad compression would not go away and then come back at random engine temperatures and run intervales would it? Same with valve timing, if it was off it wouldn't return to normal or vary with engine temperature.

Oil condition appears to be good and it doesn't smoke or burn oil so, I'm assuming the valve train and pistons are good but, I may be overlooking something.

The timing belt isn't due for a change yet but, it is getting closer to a needed service. If the belt slipped, wouldn't more than one cylinder have issues with misfires, and tailpipe exhaust would be a telltale sign wouldn't it?
 

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Discussion Starter #8
I-4 has a timing chain V6 has a belt.
Thanks! My mom's Accord SE is a V-6 and mine is the I-4 manual model. These days I do occasionally check the various sites for a V-6 manual model for a bit more fun in a low profile sedan. With all the features on my car, I'm a little surprised it has a timing chain though.
 

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Well, you could always just swap the coil around and see if the issue follows the coil to another cylinder. That usually narrows down the issue.

I would just use the OEM stuff, which is the NGK in this case. The best there is for a stock car.

Sent from GM1917, technology or something like that.
 
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Don't let the oil get low or dirty as it will cause the chain to stretch & prematurely wear the plastic guides. If the chain jumps off the sprocket you could end up with a ruined engine or a very expensive repair. My indy Honda mechanic recommends changing the tensioner every 100K.
 

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Discussion Starter #11
Thanks! I use Mobil 1 full synthetic oil so, I should be good there. Regarding the plastic guides, a great tip there! A jumped chain could cause some real havoc though, Honda cars don't have interference motors do they?

My mechanic neighbor from a few years ago really hated Mitsubishi cars because a slipped timing belt would break off valves and crater piston tops causing severe engine damage. Unfortunately, a lot of his customers were on the low end of the economic scale so, their cars were generally older and their ability to pay for a new motor was severely restricted leaving a lot of them without a vehicle to get to work, pick up kids from school, etc.
 

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I would use the NGK plugs. Check gap. Use a small amount of antisieze (silver) on the plugs. Don't over tighten the plugs in the head. Run your tank down low, fill with fresh high grade fuel. See how it runs.

Next check your codes, or clear the codes if all's running well. Check all fuses. If not running well swap the #4 coil. Still bad, without looking at my I-4 2015 EXL, if there is a wire to that coil replace it or the wires to all the coils. You may just have a shorting wire. Still running bad, do another code scan. Might also check any weather pack connectors you might see in the engine compartment. Unplug the connectors, clean with electrical contact cleaner, reconnect. Scan for codes again.

It certainly sounds like your problems are electrical.
 

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Be careful disconnecting any electrical plugs as the wires become brittle with age & can break. Some electrical connections for the 4 cylinder are no longer available to purchase new, junkyard or repair would be the only options.
 

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My mechanic neighbor from a few years ago really hated Mitsubishi cars because a slipped timing belt would break off valves and crater piston tops causing severe engine damage.
Your mom's Honda will do the same thing when the belt breaks. On your car though, the chain will likely outlast the engine.

Make sure you have the right plugs. There are a few different models (from the same plug mfgr) due to things like California emissions, ULEV/SULEV/PZEV emissions packages, etc. Each one has a different spark plug model.
 

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From 'Googling', I see these 3 spark plugs recommended most for my 2015 Accord SE I4-MT. I have an intermittent misfire again on cylinder #4 (P0304) but, I'm questioning blindly replacing the coil again after 20K~30K additional miles which are now at ~85K. The fuel injection system was professionally cleaned at ~65K miles so, I'm thinking a fuel injector issue is unlikely.

I likely have either another bad coil or some other 'wiring' issue or, the spark plug itself is becoming marginal. At ~85K miles it is time for new plugs anyway so, that took me down that rabbit hole!

Is there anything to suggest one of these spark plugs or a different model is better or significantly cheaper with essentially the same performance and longevity? The misfire sometimes is completely gone and sometimes is present. It generally is more prevalent when cold but, also occurs after getting fully warmed up. It will 'skip' occasionally or continuously cut out at ~3200RPM like a LIMP Mode is kicking in. With this intermittent nature of the miss, I am a bit puzzled as to the true cause and source of the issue. This takes me to coil-on-plug #4 again with new spark plugs.

With spark plug installation, do I need to do anything special like anti-seize on the plug threads or something else? It looks like torque is generally recommended at 11-14ft/lbs so, anything else to be aware of or consider?

I'm open to other possible causes and things to look at but, spark plugs seem reasonable at this point so I'm starting there with almost anything else I do. What am I possibly overlooking with this intermittent misfire?

Thanks!
Sid
From 'Googling', I see these 3 spark plugs recommended most for my 2015 Accord SE I4-MT. I have an intermittent misfire again on cylinder #4 (P0304) but, I'm questioning blindly replacing the coil again after 20K~30K additional miles which are now at ~85K. The fuel injection system was professionally cleaned at ~65K miles so, I'm thinking a fuel injector issue is unlikely.

I likely have either another bad coil or some other 'wiring' issue or, the spark plug itself is becoming marginal. At ~85K miles it is time for new plugs anyway so, that took me down that rabbit hole!

Is there anything to suggest one of these spark plugs or a different model is better or significantly cheaper with essentially the same performance and longevity? The misfire sometimes is completely gone and sometimes is present. It generally is more prevalent when cold but, also occurs after getting fully warmed up. It will 'skip' occasionally or continuously cut out at ~3200RPM like a LIMP Mode is kicking in. With this intermittent nature of the miss, I am a bit puzzled as to the true cause and source of the issue. This takes me to coil-on-plug #4 again with new spark plugs.

With spark plug installation, do I need to do anything special like anti-seize on the plug threads or something else? It looks like torque is generally recommended at 11-14ft/lbs so, anything else to be aware of or consider?

I'm open to other possible causes and things to look at but, spark plugs seem reasonable at this point so I'm starting there with almost anything else I do. What am I possibly overlooking with this intermittent misfire?

Thanks!
Sid
Just swap coils from one spot to another. ;
 

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A few notes and I agree with statements to rotate coil to see if code ends up at another cylinder. Also inspect plugs and see if any look much worse than the others’. Might give hints to underlying issues Denso or NGK only for Honda and whatever the manual recommends. Iridium most likely but double platinum are great too. Most fine point plugs cannot be gapped FYI.
You may check them but if wrong you need to return, not gap. Also anti-seize is awesome but can actually cause issues when used with plugs. Like over tightening and inaccurate torque readings. Also, if not torqued right can and have seen work themselves loose... Just had this issue with a recently bought Jeep and have seen often with do it yourself Ers.
 

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A few notes and I agree with statements to rotate coil to see if code ends up at another cylinder. Also inspect plugs and see if any look much worse than the others’. Might give hints to underlying issues Denso or NGK only for Honda and whatever the manual recommends. Iridium most likely but double platinum are great too. Most fine point plugs cannot be gapped FYI.
You may check them but if wrong you need to return, not gap. Also anti-seize is awesome but can actually cause issues when used with plugs. Like over tightening and inaccurate torque readings. Also, if not torqued right can and have seen work themselves loose... Just had this issue with a recently bought Jeep and have seen often with do it yourself Ers.
All spark plugs should be gap adjusted, only use a wire gauge and be very gentle. But all gaps must be inspected as same spark plug can have many applications with different gaps.
 

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Discussion Starter #19
No, coil swaps doesn't move the code including using the new one the suspect cylinder. After doing some more research, I see some Oxygen Sensor problems causing somewhat similar behavior. After swapping the coil, I drove for a while and thought things were better but, it stumbled slightly at ~2K RPM in 6th (manual transmission) and went back to normal. Then a few miles later it threw the "check engine" code and then some point after that threw three "idiot lights" (VSA, Tire Pressure, and the exclamation point Steering Wheel).

Pulling OBDII data, it is indicating a FUEL OL-FAULT in Fuel Sys #1 which suggests it is running rich because the 'upstream' Oxygen Sensor is defective.

I'm not pulling spark plugs until I have new ones available but, at this point, I am expecting to see some over fueling indications on them. Regarding excessive anti-seize and improper torque values, I have a good torque wrench so I should be able to put a proper torque spec on them (not way too much or too little) and a reasonable amount of anti-seize. Does anyone have the spark plug torque specification handy?

What I am wondering is whether I should also replace the 'downstream' oxygen sensor past the catalytic converter which I am assuming is Fuel Sys #2, though it isn't showing any OBDII codes. Do these go together when replacing one?
 

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All spark plugs should be gap adjusted, only use a wire gauge and be very gentle. But all gaps must be inspected as same spark plug can have many applications with different gaps.
NGK does not recommend adjusting their Iridium plugs, I would check the gap before installing but if I found them out of spec I'd return them : This is from their site:
"The re-gapping of fine wire spark plugs that have very small diameter platinum or iridium alloy electrodes is not recommended due to the risk of damaging the electrodes. Virtually all NGK spark plugs are set to the correct gap for the catalogue applications at the point of manufacture."
 
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