SebbySludge

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.

Video Here: Diesel Exhaust Sounds

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.

BrotatoChip

-Is the engine idling at a normal speed? Something like 750 RPM.
-You're sure you don't have a lightened flywheel? I see at least two fx100 kits, one with and one without. My brother has a '14 Si and with a lightened flywheel it had all sorts of problems until we got FlashPro on it.
-If there something going on in the exhaust it's going to require you removing and looking inside. If I remember correctly the "header" is case into the cylinder head and the cat bolts up right afterwards. You can't really unhook part of the exhaust to test.

SebbySludge

- The car is idling like 700/750rpm it seems 100% normal at idle. It definitely idles the same as my previous K24z7 which ran fine for 144k till the rings/head gasket gave out.

- Wouldn’t the car just go into limp mode if i had a lightweight flywheel without misfire disabled? (Not trying to fight you or anything that’s just what i read personally). Also wouldnt the issues have started from the second i was running the engine? I did 4000miles with no issues at all. I bought it at a local Honda performance shop thats super well rated and i made it super clear multiple times in the convo i need something for a stock car.

- I’m starting to think the major misfire on Monday was just cause I was a bit low on gas and the pump just freaked out and the exhaust sound is just an exhaust with 148k on it failing internally. Ive put over 200miles on it now since this has started and theres no issues besides this weird exhaust note i even took the car up to redline a few times today to see what would happen feels/pulls fine. I’d probably have to remove the whole exhaust to check it out and see whats going on sounds like a pain lol.

BrotatoChip

That sounds normal to me.

You probably got the right one then. With my brother's it had all sorts of errors after just a few miles of driving. I didn't realize you have already gone 4,000 miles.

I'm leaning towards something in the exhaust. I would like to think it would be something at the cat or before.

SebbySludge

Thanks for the info/opinions I think at this point my best bet is too keep driving it and see what happens. Assuming nothing happens by the time it gets warm out again maybe ill drop the exhaust and see what’s going on, but that will have to wait it’ll after winter unless i have any more issues.

BrotatoChip

That is exactly what I would be doing. Keep driving it until you having issues other than the sound.

SebbySludge

appreciate the info/help! Hopefully it doesn’t go further than the sound.