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Discussion Starter · #1 ·
Alright y'all. Looking for some ideas.

I was doing some preventative maintenance on my 06 civic with 204k miles. No issues or faults whatsoever.

I changed the serpentine belt and spark plugs. That's it.

I got misfire faults on all cylinders and the random misfire fault also. No issues with power or idling.

  • I dont have the old plugs. Threw them away. I wish I could pop them in and try them.
  • I had a heck of a time getting the plugs out. I was really pushing on the wrench even after applying pb blaster and all that for some time. I was seriously thinking the plugs were going to break in the head. It was very odd that they remained hard to turn throughout the whole thread engagement. Not just the initial breaking free.
  • I had NGK laser iridiums in there since 100k miles. I went with the NGK iridiums (non laser) this time around NGK 97138 which are supposedly compatible.
  • Coils look fine. I doubt they'd all go bad at once during the removal process.
  • I did put antiseize on the new plugs but got a second set thinking maybe they were damaged or the antiseize did something, 2nd set of new plugs went in dry and still seeing the fault (torqued to spec).

I'm not sure where to go from here. Threads in the head look ok. I can spin the plugs in pretty well. All I did was change the darn plugs and got these faults.

Anyone have issues with these plugs? Should I go back to the laser iridiums?
 

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Alright y'all. Looking for some ideas.

I was doing some preventative maintenance on my 06 civic with 204k miles. No issues or faults whatsoever.

I changed the serpentine belt and spark plugs. That's it.

I got misfire faults on all cylinders and the random misfire fault also. No issues with power or idling.

  • I dont have the old plugs. Threw them away. I wish I could pop them in and try them.
  • I had a heck of a time getting the plugs out. I was really pushing on the wrench even after applying pb blaster and all that for some time. I was seriously thinking the plugs were going to break in the head. It was very odd that they remained hard to turn throughout the whole thread engagement. Not just the initial breaking free.
  • I had NGK laser iridiums in there since 100k miles. I went with the NGK iridiums (non laser) this time around NGK 97138 which are supposedly compatible.
  • Coils look fine. I doubt they'd all go bad at once during the removal process.
  • I did put antiseize on the new plugs but got a second set thinking maybe they were damaged or the antiseize did something, 2nd set of new plugs went in dry and still seeing the fault (torqued to spec).

I'm not sure where to go from here. Threads in the head look ok. I can spin the plugs in pretty well. All I did was change the darn plugs and got these faults.

Anyone have issues with these plugs? Should I go back to the laser iridiums?
Did the new plugs come pre gapped?
 

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Discussion Starter · #6 ·
Things have taken a drastic turn for the worse.

I had read 2 cases in my interwebz search that guys had misfire faults due to a belt idler issue. I started looking at it closely and it did look like it was dancing quite a bit put a long screw driver on there and isolated a noise. When I started the car to pull it I to the shop this morning it was very loud.

Long story short. The tensioner bolt has broken in the block and I'm in the process of trying to extract it. Joy.

I do think the misfire fault was tied to my tensioner. I'll see if I can get this all back together and report back.
 

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Discussion Starter · #7 ·
245103

Harbor freight left hand drill bits for the win. I had to drop the engine on the passenger side as far as it would go. Drilled with the 3/32 first then when willing with the 1/8th the boot piece came out.
 

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Discussion Starter · #9 ·
Bad news. New tensioner (and water pump since I was already there) on the car and after a test drive the misfire fault is back.

At this point I'm thinking trying the same type of plug I used to have (laser iridium ngk) might be worth the expense just to rule that out.
 

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Discussion Starter · #10 ·
OK got the NGK Laser Iridiums in. I drove about 100 miles this afternoon (previously I could get the lamp to flash in about 10 miles). City/highway. I did about 6 stops at stores. No faults, I was feeling pretty darn good, like i'd solved it.

Literally as I turned onto my road, I saw all 5 misfire faults pending (not active yet)....UGH.
 

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Discussion Starter · #11 ·
Welp, after some more driving the misfire faults never went full active and haven't come back (not even pending). I'm willing to call this resolved by spark plug incompatibility.
 

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Discussion Starter · #12 · (Edited)
OK. Bad news to report, success was short lived. Misfire faults came back. They are fairly frequent. Over the last few weeks I've had a handful of times where the MIL actually flashes and I get an actual misfire, bad enough the car isn't drivable. Curiously enough if I just key off and key on (not clearing codes) the misfire goes away (MIL lamp still on). I will add that when the MIL is flashing and the car is stumbling the fuel system ststus reads as 'OL -fault'. Not entirely sure what that means. But for the most part the MIL will just come on but there is no actual misfire felt, performance wise.

I've done a few things since the last update, not really thinking it would help but more of a hail mary.
  • Replaced coils (with Denso/OEM ones) - I'm at 200k miles, so probably not a horrible idea.
  • Cleaned the EGR Valve.
  • Checked valve lash (intakes were a little towards the loose end of the spec, brought them back to middle of the spec).

Running out of ideas on this one!
 

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Discussion Starter · #14 ·
Could it be a short or a ground fault somewhere? I hope it isn't the computer or something.
I went througha few grounds and didn't see anything tgat eould cause concern but cleaned them anyway. I do have the factory service manual so ill try and run down the wiring for some troubleshooting.

This is a relatively early 06, so wondering if it could use a software update. I combed through a few TSBs but nothing stood out as a culprit.

I did buy a set of denso plugs (OE brand but not OE part number, platinum vs laser iridium). They are substantially different with how much they protrude into the cylinder.

In the attached pic, NGK left and Denso is right. Fingers crossed.
 

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