Exhaust smell after header install

[Yoshoobaroo]

Originally Posted by HaXx

While were all talking about catless headers, can I ask if anyone has used an o2 sensor spacer to not upset the downstream sensor on a catless header? The j shaped vibrant performance one seems to have raving reviews. I dont want to spend hundreds to re-protune. Dont shoot me

It doesn’t really work. Intermittently at best. You need a tune to get the power out of the header anyway

[Yoshoobaroo]

Originally Posted by HaXx

Give it to me straight, just how bad does a properly installed, no exhaust leak, full catless header and front pipe system small inside the cabin?

It smells like shit. Even high flow cats smell. You won’t smell it in the car, but if you have the windows down you will. If you get something from the trunk when it’s running it smells disgusting. Honestly not worth the 10hp to me.

[HaXx]

I've gotten some mixed information over the years that some of you might help clear up for me.

I am confused. some say that punching out/installing catless header without a tune will make it run lean or rich(dont remember which)

Then others have said that the upstream o2 sensor is the one that talks to the ecu, so nothing would change at that sensor, so the air/fuel remains. the downstream sensor is just responsible for tripping the code when theres no cat.

I know the whole point of catless is to make more power, so why wouldnt I want to retune after? Well, I'm generally happy with the cars power, just looking for a cheap exhaust upgrade.

[NoHaveMSG]

Originally Posted by HaXx

I've gotten some mixed information over the years that some of you might help clear up for me.

I am confused. some say that punching out/installing catless header without a tune will make it run lean or rich(dont remember which)

Then others have said that the upstream o2 sensor is the one that talks to the ecu, so nothing would change at that sensor, so the air/fuel remains. the downstream sensor is just responsible for tripping the code when theres no cat.

I know the whole point of catless is to make more power, so why wouldnt I want to retune after? Well, I'm generally happy with the cars power, just looking for a cheap exhaust upgrade.

In open loop it could be lean. In closed loop it should compensate.

[DarkSunrise]

Originally Posted by Yoshoobaroo

It smells like shit. Even high flow cats smell. You won’t smell it in the car, but if you have the windows down you will. If you get something from the trunk when it’s running it smells disgusting. Honestly not worth the 10hp to me.

I had a HFC on my car at one point and when a friend and I were driving to the track (he was behind me in a different car), he mentioned that the smell was nauseating over a 2-3 hr drive. I personally didn't notice much from inside the car though.

But yeah I've since gone back to having both OEM cats in place. Not worth it for minimal power gains, plus after we had our kid, my wife didn't want him breathing that.

[Irace86.2.0]

Originally Posted by HaXx

I've gotten some mixed information over the years that some of you might help clear up for me.

I am confused. some say that punching out/installing catless header without a tune will make it run lean or rich(dont remember which)

Then others have said that the upstream o2 sensor is the one that talks to the ecu, so nothing would change at that sensor, so the air/fuel remains. the downstream sensor is just responsible for tripping the code when theres no cat.

I know the whole point of catless is to make more power, so why wouldnt I want to retune after? Well, I'm generally happy with the cars power, just looking for a cheap exhaust upgrade.

I already posted this earlier, but here it is again. These guys seem to know more than me...

Question:

People have often stated that the oxygen sensor installed behind the catalytic converter in a common gasoline engine setup has only one function: to test the health of the catalytic converter. Specifically, that it plays no role in engine mixture control. There is generally no disagreement with the role in catalyst testing. The question: are there any engines where this sensor is used by the engine control computer to modify the fuel mixture or other operating parameters?

Answer 1:

The rear fuel control controversy has been the subject of some interest on professional automotive repair forums in years past, principally i-ATN. Rear fuel control strategies are used extensively; this is a well-established fact within the industry. For a more accessible reference source; the Bosch Automotive Handbook is a good reference. In the 5th edition, it's on page 525.

Engine management fuel control strategies are among the most closely guarded secrets. Documentation is scarce on the details of how it is done in any given system. That does not mean we are without ways to discover generally how it is done. One piece of evidence we have is the OBDII PID labeled O2BxS2FT. A fuel trim PID for a rear oxygen sensor suggests that the after catalyst sensors are indeed used for fuel control. Experimentation can also reveal how the different OEMS use the sensors. Some systems, Subaru of the late 1990's for example, are unable to maintain mixture control at or near stoiciometric when the pre-catalyst sensor becomes disabled. Others have no problem maintaining fuel control on both banks even when only one rear sensor is operative (1990 Lexus LS400).

Fuel control strategies have changed over the years. In the 1970's and early 1980's system designs tended toward simple direct feedback logic. The mixture sensor sends its signal, the controller adjusts the mixture via changes to the injector on time, combustion happens, and then the sensor reads the new adjusted mixture, and so the feedback cycle continues. This system works but is crude by current standards as it is mediocre when it comes to optimal fuel mileage management and very poor at the fine level of mixture control need by the catalyst for optimal emission control. This is the system design commonly known and quoted among technicians and amateur internet forums. It is where the myth that the rear mixture sensor only tests the catalyst comes from.

Newer designs have changed significantly. This logic type has been labeled "feed forward". It uses Neural Network learning logic and memorized previous engine response parameters to achieve fuel control that gets a clean tailpipe and better power.
This method uses an air fuel ratio sensors pre-cat and standard O2 sensor post cat. The AFR sensors test for misfire detection, mixture variation among cylinders and exhaust temperature. The rear sensor checks average mixture, catalyst output temp, and for a few seconds when conditions are right monitors catalyst heath. Direct feedback is not used as it is much to slow to keep the mixture in the range needed.

Fuel control logic varies greatly over the years and between manufacturers. Blanket statements about how it is done are unlikely to be supportable. However, one can discern some of how it is done on any given vehicle by watching graphed mixture sensor data on an extended test drive.

Answer 2:

I'll summarize what the Bosch Automotive Handbook, 8th edition, says:

--the upstream lambda sensor is heavily stressed by high temperatures and untreated exhaust gas, which impacts sensor accuracy as voltage readings can shift due to changing exhaust gas compositions.
--downstream lambda sensors are not as susceptible to impact on sensor accuracy, but are slower to respond to dynamic changes and mixture changes
--Two-sensor lambda control combines the beneficial aspects of both upstream and downstream sensors

"Greater accuracy is achieved with two-sensor control.

Here, a slower correction control loop is superimposed on the two-step or continuous-action lambda control described by means of an additional two-step lambda sensor.

The voltage of the two-step sensor downstream of the catalytic converter is compared with a set point value (e.g. 600 mV) for this purpose. On this basis the control evaluates the deviations from the set point value and additionally alters additively the controlled rich or lean shift of the first control loop of a two-step control or the set point value of a continuous-action control."

Practical example from my BMW M5



--The "additive" values are the additive corrections based on the downstream sensors, as described in the quote above.
--The "multiplicative" values are the traditional fuel trim correction values based on the upstream sensors.

[solidONE]

Also about running catless on a streetcar. If you or I can smell a modified exhaust, dont you think your local hwy patrol officer knows what they smell like as well?

[Ernest72]

Originally Posted by solidONE

Also about running catless on a streetcar. If you or I can smell a modified exhaust, dont you think your local hwy patrol officer knows what they smell like as well?

All depends where you live. Here in NY I have smelled plenty of catless Subaru’s, cops don’t do much. More likely to get you for tint or loud exhaust.

Personally I always keep at least one cat (the furthest back I can). It helps with smell for sure.

[solidONE]

Originally Posted by Ernest72

All depends where you live. Here in NY I have smelled plenty of catless Subaru’s, cops don’t do much. More likely to get you for tint or loud exhaust.

Personally I always keep at least one cat (the furthest back I can). It helps with smell for sure.

Well, in the home of Fast & Furious, SEMA association and 'West Coast Customs Chop Shops' the police know how to write you up for every-fkn-thing, even stuff you didnt realize was not legal.

[Yoshoobaroo]

Originally Posted by solidONE

Well, in the home of Fast & Furious, SEMA association and 'West Coast Customs Chop Shops' the police know how to write you up for every-fkn-thing, even stuff you didnt realize was not legal.

Your ignorance of the law does not protect you from it.
Hell, everyone in the US that removed cats is at risk because it's illegal to remove them on a federal level. Most no-inpection states don't have robust reporting mechanisms so you can get away with it for a long time, but if a dealer is feeling overzealous the can report your car as non-compliant.

Violators are subject to civil penalties up to $45,268 per noncompliant vehicle or engine, $4,527 per tampering event or sale of defeat device, and $45,268 per day for reporting and recordkeeping violations. 42 U.S.C. § 7524; 40 C.F.R. § 19.4. The EPA often uses the Mobile Source Civil Penalty Policy to arrive at an appropriate civil penalty for vehicle and engine enforcement settlements.

[solidONE]

Originally Posted by Yoshoobaroo

Your ignorance of the law does not protect you from it.
Hell, everyone in the US that removed cats is at risk because it's illegal to remove them on a federal level. Most no-inpection states don't have robust reporting mechanisms so you can get away with it for a long time, but if a dealer is feeling overzealous the can report your car as non-compliant.

That service writer must have a very sadistic sense of humor.. or just outright mean.

Like.. I'm paying you how much for an oil change and you did what? And your 'diagnostic fee' is how much?

[Ernest72]

Originally Posted by Yoshoobaroo

Your ignorance of the law does not protect you from it.
Hell, everyone in the US that removed cats is at risk because it's illegal to remove them on a federal level. Most no-inpection states don't have robust reporting mechanisms so you can get away with it for a long time, but if a dealer is feeling overzealous the can report your car as non-compliant.

Never heard of a business doing it, but I have heard (on forums) of some young punks busted for speeding and loud exhausts that had to put a cat back on and get it inspected to avoid a penalty in NY. But likely they took it off a day later.

[Contender]

Thank god I don't live in NY...I am running catless no smell in car even with windows down can smell it if I back up with windows down but that's no biggie..outside you can smell it but, thats fine by me. Reminds me of my 71 Mach 1 Mustang.

[Ernest72]

Originally Posted by Contender

Thank god I don't live in NY...I am running catless no smell in car even with windows down can smell it if I back up with windows down but that's no biggie..outside you can smell it but, thats fine by me. Reminds me of my 71 Mach 1 Mustang.

My 69 cutlass would turn snow black in the winter. Cars these days are way cleaner than back then.