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Discussion Starter #1 (Edited)
Hey guys, been having an issue with my 2012 Civic Si Sedan and this post is one of my last resorts before taking the car to the dealer which I’d like to avoid doing. Basically if you stand near the exhaust it honestly sounds like a diesel engine I’m gonna get a video uploaded ASAP, but here’s the break down of whats going on.

End of August my head gasket went at 144k, the car burnt oil like crazy due to the piston rings being shot and by the time it started it was too late for Honda to do anything about it. So, I found a low mileage engine at a junkyard grabbed it and my Dad’s buddy swapped the engine, while he had it out he installed a Clutch Master FX 100 kit (none light weight flywheel car is stock and i don’t have a FlashPr). When the swap was done we used new oil and filter, new coolant car started first key turn, no issues. After I put a 1500 miles on it my Dad and I did an oil change and changed the plugs just to see what everything looked like, oil looked great and plugs also looked fine. I put another 2500 miles on it or so i was at 148,5xx when the problem started last Friday. I noticed the car sounded a bit strange at idle and when i walked around to the back of the car i noticed it sounded like a Diesel engine (again ill post a video ASAP). It was raining Saturday and Sunday so I couldn’t really check anything and than Monday when i woke up to go to work i made it around the corner from my house when the car had a major misfire check engine light flashed car bogged and was super weak, I shut it off back on and babied it home the CEL never actually stayed on it just flashed when the car had the major misefire, I called the guy who did the swap and asked him if he could come check it out. He plugged in his computer (not sure exactly what but some fancy Snap On with a fancy touch screen) and there was no stored codes we drove around for 10 miles or so, no issues besides the weird idle/exhaust . So at this point I’ve put over 150 miles on the car no CEL, no more major misfires, just the weird idle/exhaust drives completely fine otherwise. Here is everything we’ve done:
  • new gas
  • fuel injection cleaner
  • new NGK Iridium Plugs
  • new OEM plugs
  • MAF replaced
  • Throttle Body Cleaned
  • Intake Manifold Gasket checked for leaks
  • when monitored for like 30+ mins on 2 different advanced computers the only thing we could find is the car running a hair rich and from what 2 different mechanics i know who looked at the car for free (guy who did the swap and another buddy) said the running a bit rich could be within margin of error
  • multiple attempts to air out the coolant system, theres no way there any air left in there anywhere.

We cant figure out anything, I was originally thinking an exhaust valve was on its was out, but idk now. Could the cat or exhaust be clogged or partly clogged somewhere and maybe causing the exhaust to sound like this? Any ideas? I drive a lot for work and only have 27 days left on parts warranty before i cant return the engine and am beat if anything serious happens. Appreciate any help/ideas.

UPDATED: Video Post Exhaust Diesel Sound
 

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Definitely sounds like it's misfiring.

Have you confirmed the mechanical timing is correct? Was the engine compression tested before install, you could have a cylinder down on compression.

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Discussion Starter #4 (Edited)
Definitely sounds like it's misfiring.

Have you confirmed the mechanical timing is correct? Was the engine compression tested before install, you could have a cylinder down on compression.

Sent from my SM-G973U1 using Tapatalk
Engine was not compression tested at any point it supposedly only had 34,000 on it at time of install so i really didnt think there was a need nor did i have the tools available off hand at the time. Correct me if I’m wrong, but wouldn’t i feel a power loss if compression was low? When this engine was installed i felt like it had a solid 15-25 more horsepower than my old one before it died it felt and still feels strong, healthy pulls good. Also just strange this issue started after 4000miles of the car running 100% fine. Timing wise nothing was opened up and checked but computers did not indicate any timing issues while the car was running.

Ive put over 200 miles on it since it freaked out on Monday and I’m starting to think that may have been an unrelated freak out, i was kinda low on gas when it happened maybe the fuel pump freaked out causing the engine to misfire? Ive even taken the car to redline a few times now and I haven’t had any issues. I’m starting to think at maybe the exhaust sound is an issue with the exhaust being clogged or messed up internally since the car is about to hit 150k and I’m in NJ. When listening to the car from the engine bay it sounds 100% normal. It just from the exhaust end you can hear that which is leading me away from a misfire issue.
 

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My '12 Si exhaust garbles slightly at idle (more so cold starts) but when listening from the bay there are no misfires and it's idling smooth. I chocked it up to the exhaust pulses 🤷‍♂️ No misfire codes.

Edit: I will listen to your video tonight and see if it's the same as my exhaust
 

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Discussion Starter #6
My '12 Si exhaust garbles slightly at idle (more so cold starts) but when listening from the bay there are no misfires and it's idling smooth. I chocked it up to the exhaust pulses 🤷‍♂️ No misfire codes.

Edit: I will listen to your video tonight and see if it's the same as my exhaust
Hey man that would be amazing please let me know if yours should similar that would give me at least a little piece of mind.
And yeah I’m starting to thing it’s just the exhaust itself showing its age/wear. Maybe I’ll drop the exhaust in the spring see what it looks like.
Thank you man!
 

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Hey man that would be amazing please let me know if yours should similar that would give me at least a little piece of mind.
And yeah I’m starting to thing it’s just the exhaust itself showing its age/wear. Maybe I’ll drop the exhaust in the spring see what it looks like.
Thank you man!
I recorded some audio clips with my condenser mic this weekend but was too busy to edit them together. I'll post it sometime in the next few days!
 

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Discussion Starter #12
Not really sure what else I can add. Other than a potential exhaust leak?
OP states the car is running normally so it makes it very hard to diagnose based on sound alone.

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Yeah idk what other info to give ive put 1000miles on the car since this started and driving wise its fine, hits vtech without any issues and pulls as hard as it always has. Idk its just weird and definitely not normal in comparison to my old engine and again this started after like 4K miles which just makes me more confused. I think I’m just gonna have to wait till spring, drop the exhaust and see if theres any obvious issues.
 

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Maybe @dpetro1 can shed his insight if we ask nice enough. Lol

Sounds like mine. Not an expert by any stretch, but sounds normal to me.

Yeah idk what other info to give ive put 1000miles on the car since this started and driving wise its fine, hits vtech without any issues and pulls as hard as it always has. Idk its just weird and definitely not normal in comparison to my old engine and again this started after like 4K miles which just makes me more confused. I think I’m just gonna have to wait till spring, drop the exhaust and see if theres any obvious issues.
Maybe take another vid. Your original is pretty noisy. Lots of wind noise that is distorting the rest of the audio. Also, not sure if it's just me, but it helps to have the actual video along with the sound.
 

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Okay, now I can clearly hear it. No leaks on the DP side of the head either? That's odd how it seems to get worse as it starts to warm up.
 

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Discussion Starter #16
Okay, now I can clearly hear it. No leaks on the DP side of the head either? That's odd how it seems to get worse as it starts to warm up.
Not as far as i can tell after the engine was replaced i put 4000 miles on it before this started happening so its just weird that it started out of nowhere like this.

Also a redone warmed up video will have to wait a few days, something is going on with my shifter linkage so 2,4,6 reverse dont grab. Once i get that handled ill get a new video of the car warmed up.
 

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Run a compression and vacuum test on each cyl. You may not glean any new info, but you'll at least cross shit off the list.
 

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Discussion Starter #18
Run a compression and vacuum test on each cyl. You may not glean any new info, but you'll at least cross shit off the list.
Sorry it’s dark, I finally for the car going again after the shifter cable issue and just wanted to get some more info on here ASAP. I can take another video during the day if need be. This is warmed up after about a 20-30mins drive.
Weird idle Warmed up

Also here’s a picture of the plugs that were only in the car for 2500 miles. These were pulled out of the car when the issue first started and only have about 2500 miles on them as I change the oil and plugs after the first 1500 miles on the new engine.

At this point it’s unfortunately getting cold out and I’ll probably have to wait till spring to do any serious diag unless the issue gets worse or something else happens. All my days off have been freezing.
 

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Maybe double check that plug gap. Should be pregapped to 0.044". Hard to tell from the picture but those look gapped pretty big.

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Maybe double check that plug gap. Should be pregapped to 0.044". Hard to tell from the picture but those look gapped pretty big.

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those are not the plugs currently in the car. I replaced them when I pulled these out just to be safe and we did double check the gap before installing the new ones.
 
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