Exhaust smell after header install
 

Hey guys so I have an issue and it’s driving me nuts. My car definitely smells like it has an exhaust leak after installing my JDL header. I installed the header and the next day I had a 13.5 hour trip. I could definitely smell exhaust fumes inside my car. A little after 4 hours into my trip I stopped at a shop and I had them take a look. They said everything looks great and I could do a smoke test for 90 bucks. I said yeah let’s do it... it passed the smoke test with no leaks anywhere. Guy at shop said it could be the anti seize I am smelling and cleaned my header of the little bit I got on it. Well I’m chugging along all on the interstate and when I wide open throttle I can definitely smell it. I froze my ass off with windows down because I definitely got a headache from the fumes. This isn’t my first header install on a car. I’ve never had this issue before. I know the header has a cat but almost every single manifold I’ve replaced was catted and I swapped it out with a cat less header without ever smelling the exhaust inside the car. The other day I went to start my car outside to let it warm up with windows up. Mind you this is outside not in a garage and when I got into my car it smelled awful.
The header is JDL ceramic coated header I bought it new, also installed grimspeed gaskets. I torqued everything to spec and I did the heat cycle and torqued it down again. Only other mods are a greddy cat back exhaust but I had it prior to header and never smelled anything. A Perrin inlet tube and K&N filter but once again never smelled anything till after the header install. I also upgraded from oft v1 to v2+ tune. I know you’ll get a little smell from taking a cat off but not enough to smell it inside your damn car when you idle it for 5 mins with windows down. Any advice would be greatly appreciated. Because I’m lost and if I can’t figure it out I’m swapping back to the original manifold and selling the headers.

is your cat clogged or burned out from running too rich?

I've dealt with this on another car.
Sometimes people like to get under the car while it's running and try to feel air coming out of possible areas that leak but that can be hard at times so try this.

1. Remove the header
2. Look at the gaskets (both the ones going to the heads and the one going to the overpipe). If they are sealing correctly you'll see black soot in a perfect circle. If it's leaking you'll see it on the gaskets spraying out of the perfect circular shape you'd hope for.

Since the header installation didn't happen too long ago not enough time may have passed before seeing any soot on the bottom of the heads or surrounding areas. The gaskets would show the leak first. So I'd remove it and examine the gaskets. Maybe buy new ones before doing this so you can put fresh ones on. It's worth noting I've NEVER had a problem with stock Subaru gaskets.

Also check the welds, there could be a bad weld.
In addition, check the overpipe to the front pipe connection.

Regarding the smoke test...where did they supply the smoke? I have another question but I'll let you answer first.

Create bubble water and spray over header to find the leak.

This will work. But I have had success getting under the car, but you gotta feel around. Helps to get someone rev while you are under there. Make sure it’s on jack stands or ramps and safe.

Also do you have the sound generator removed. Did you plug the hole to the inside of the car. Some people have gotten some smells inside the car through that hole.

Yes the sound generator is removed. I didn’t plug the hole. I’ll look into that!

I’ll definitely look into that. I had a 890 mile trip after I installed it. I’ll order new Subaru gaskets and hate my life taking it all apart again but I totally see what you are saying! I did torque the header bolts to the 22 pounds. The 02 sensor I just tightened till it felt good. I could always check the 02 to make sure it’s not leaking I just thought of this.

The smoke test they did it via tail pipe I believe. They said it pinged back with no leaks anywhere or something like that I can’t fully remember. It was a few weeks ago but I was exhausted from a 26 hour round trip in 3 days. Long story short I’m working in Maine and my car was in Ohio. I decided to stay in Maine during all this corona going on. I drove a rental to Ohio to grab my brz. While I was home I installed my header I ordered and a few other odds and ends inside. Was hoping to get my coilovers on but I was too tired and no place was open for an alignment.

I chased an exhaust leak for a while. I'd try pulling the gaskets and looking for signs of a leak. Pretty easy to see where the soot is escaping.

Since you have an OFT, you can do some datalogs and see how your fuel trims are doing. Large positive fuel trims (LTFT) at partial throttle can be indicative of a leak located near the O2 sensor.

I'd also verify that it is indeed an exhaust leak and not something else. The stock header, OP and heat shields can catch oil dripping off the rear cam cover. I remember when I replaced the header/OP with non-heat shielded versions, I could smell the oil burning on the bare exhaust parts once they heated up. The fumes would go directly to the hvac and would enter the cabin. Different smell than exhaust though, more caustic and less fuely.

I’ll look into that on my way home. I did get the ceramic coated header for heat reasons. The smell isn’t burning oil. It’s definitely exhaust for sure. I’ve had my fair share of Honda’s that burned oil in vtec and that definitely isn’t the case here.

Is it a catless header? It will smell more just because your cat efficiency is so much worse, the primary cat does most of the work after all.

There is a technique to increase the effectiveness of finding a exhaust leak using soapy water.

Plug your tailpipe or duct tape to seal it then shoot compressed air while you look for leaks. Or plug it up or restrict the exhaust while its idling.. the increase in pressure will make the leaks more obvious to find.

When I installed my JDL headers earlier this year they smelled really bad for about the first week of driving. The smell is completely gone now.

From what I've read it takes the ceramic coating several heat cycles to fully cure.

The main cat does most of the work. The precat is not necessary once the main cat heats up, but you are right about the smell. It should smell for 10 minutes (depending on temp/driving conditions) until the main cat fully heats up.

^^^ This.

Use a feather or something that is easily effected by a wind current.

If you use your hand to feel for an exhaust leak then spray alcohol on your hand. The air from an exhaust leak will be more noticeable kind of like how someone will lick their finger before putting a finger in the air to sense the direction of the wind, say for a field goal kick.