I installed the Topspeed header and RT cat two weeks ago. I've noticed a slight gas mileage decline which I initially attributed to my lead foot enjoying the new mods. However, it seems to be persisting a bit, and I also occasionally (but not consistently) notice an odd smell after getting out of my car.

I've done some searching and it turns up a lot about primary 02 sensor failure. I'm pretty confident that I didn't damage the primary 02 sensor during my installation, because despite living in the rust belt, removing the 02 sensors was probably the single easiest part of the job.

Could it just have gone on its own? As I understand things, if the primary 02 sensor craps out, your A/F ratio is going to be shot to hell, causing the car to run rich.

Is there anything else I could check for or any easy way to test this short of having the dealership look at it? The part runs $230 or so and seems like an easy DIY job so I wouldn't pay them labor to fix it, I'm just not eager to throw $230 away if my 02 sensor is fine.

Thanks for any input.

- Matt, who was really hoping to stop spending money on his car until the spring!

 

I suppose the only way to know for sure is to get an AFR from a dyno or some other source.

Annecdotally I will mention that when I was using an icebox on my tsx I noticed a bit of a different smell from the exhaust and much more residue on the exhaust which would indicate it running richer.

I have a suspicion that it may be somewhat normal given breathing modifications but I'll let other people chime in with their own experiences

 

You can also get the A/F ratio from the ODBII port. This is a reading that comes straight from the ECU.

If you really messed up your O2 sensor, you would probably throw a CEL. Also a faulty O2 sensor will cause your car to rich, but only slightly. If the ECU senses the O2 sensor is messed up it will put the car in limp mode and have it maintain an A/F ratio of 14.0. It will also not let your car go into open loop anymore so you would notice reduced performance.

More of a rich gas smell is not uncommon when you first get a hi flow cat. Just keep driving and see what happens. If you're really worried, try to get something that lets you read the A/F ratio from the ODBII port. I don't know if Autozone has a loaner ODBII tool that reads this also. A healthy o2 sensor will maintain an A/F ratio of 14.7 at idle and cruising.

Good luck!