Exhaust in vents...then no exhaust in vents

[VicVinegar]

The jury is still out on it "fixing" itself, but figured I would throw it out to the hive mind here. Car is my Civic in the sig.

I apparently have a failing cat converter, and at the time that was diagnosed, mechanic said the front pipe was getting close to going too. I was planning on getting those pieces replaced soon anyway, but within the last week, my exhaust note changed (even at idle) and I started getting exhaust in the vents when I ran the heat. Obviously it was worse when I was stuck in traffic. Last time I drove it, I ran the heat and didn't get anything.

I have an appointment for Wednesday to get this checked out, and as long as it isn't something expensive, I'll get everything patched up. I'm just wondering what it could be. Still no check engine light by the way. First thoughts were possibly the front pipe went, but I am not sure if it is far enough up to get into the HVAC system. Then the exhaust manifold gasket could be leaking, and possibly a cracked manifold. The fact I noticed no exhaust last trip now has me stumped. Any ideas as to what could come and go? Or was that last trip just a freak occurrence? I also noticed the "extra" noise at idle was gone. Thanks for the opinions.

 

[Mopar618]

You seem to be on the right track with considering what the possibilities may be.

Honestly if you want to check the pipe condition, take a minute to use some channel locks and gently squeeze to see how the integrity of the pipe is holding up (I say gently because you obviously don't want to crimp the pipe).

Otherwise, as for the leaks, if there are no immediate concerns underneath (cracked welds, general holes, etc.), it honestly sounds like it's coming from up top. Meaning, you're probably on the right track with the manifold being cracked or the gasket being worn. Examine the manifold and try to listen for where the hiss of the leak is coming from, and go from there.


Hope this helps in some way.

 

[Fazzone]

This is a long shot but check and see if the exhaust manifold is cracked. My sister has a 2000 Civic and I spent an hour trying to track down an exhaust leak. I finally noticed some carbon on the manifold around the cracks. If I remember correctly it was cracked on cylinder #3.

 

[VicVinegar]

Thanks for the input. No issue with exhaust smell on the drive in today. Unfortunately I won't have the time to get under it myself these next couple days, but like to be prepared with possible causes for bringing it to the shop. The fact it went away after a few days of consistent exhaust coming through had me a little thrown.

Unfortunately my research found more than a few tales of cracked manifolds on this vintage Civic,

 

[Propflux01]

You prolly just had the right conditions of airflow allowing a leak to let the exhaust smell get into the vents. As for the noise, could have been some rust moving around temporarily uncovering a hole (depending on how bad the pipes are rusted) changing the tone. I'm sure it'll all go away when you get the exhaust replaced.

 

[VicVinegar]

Turned out to be a shot 13 year old gasket between the front pipe and cat. Also took care of my rattling. Explains why the original diagnostic of a broken cat didn't result in a check engine light. The cat was working fine. Very happy though to not have to pony up for the new cat. Also glad the mechanic took the time to check everything over again. Could have very easily sold me a cat I didn't need.

 

[Mopar618]

Very good, I'm glad to hear it is taken care of.

Also, if that exhaust mechanic did that type of job for you, stick with them in the future for other issues. I've been doing various exhaust jobs for a few years with a "mentor" of mine that used to own an exhaust and brake shop, and it's hard to run across exhaust mechanics that do that type of work. Props.