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I want headers but what about the CEL?

1M views 188 replies 93 participants last post by  troy.doggett88 
#1 · (Edited)
Well after explaining the CEL and header predicament in our cars a few times I figured it would be a good idea just to create a thread that can be referred to.

First off, lets learn about what 2 key components are critical when it comes to headers and a CEL, catalytic converters and oxygen sensors.

What is a catalytic coverter and how does it work?

A catalytic converter is a device that uses a catalyst to convert three harmful compounds in car exhaust into harmless compounds.

The three harmful compounds are:

Hydrocarbons (in the form of unburned gasoline)
Carbon monoxide (formed by the combustion of gasoline)
Nitrogen oxides (created when the heat in the engine forces nitrogen in the air to combine with oxygen)
In a catalytic converter, the catalyst (in the form of platinum and palladium) is coated onto a ceramic honeycomb or ceramic beads that are housed in a muffler-like package attached to the exhaust pipe. The catalyst helps to convert carbon monoxide into carbon dioxide. It converts the hydrocarbons into carbon dioxide and water. It also converts the nitrogen oxides back into nitrogen and oxygen.

What is an oxygen sensor and how does it work?

Every new car, and most cars produced after 1980, have an oxygen sensor. The sensor is part of the emissions control system and feeds data to the* engine management computer. The goal of the sensor is to help the engine run as efficiently as possible and also to produce as few emissions as possible.

*A gasoline engine burns gasoline in the presence of oxygen . It turns out that there is a particular ratio of air and gasoline that is "perfect," and that ratio is 14.7:1 (different fuels have different perfect ratios -- the ratio depends on the amount of hydrogen and carbon found in a given amount of fuel). If there is less air than this perfect ratio, then there will be fuel left over after combustion. This is called a rich mixture. Rich mixtures are bad because the unburned fuel creates pollution. If there is more air than this perfect ratio, then there is excess oxygen. This is called a lean mixture. A lean mixture tends to produce more nitrogen-oxide pollutants, and, in some cases, it can cause poor performance and even engine damage.

*Th*e oxygen sensor is positioned in the exhaust pipe and can detect rich and lean mixtures. The mechanism in most sensors involves a chemical reaction that generates a voltage. The engine's computer looks at the voltage to determine if the mixture is rich or lean, and adjusts the amount of fuel entering the engine accordingly.

The reason why the engine needs the oxygen sensor is because the amount of oxygen that the engine can pull in depends on all sorts of things, such as the altitude, the temperature of the air, the temperature of the engine, the barometric pressure, the load on the engine, etc.

When the oxygen sensor fails, the computer can no longer sense the air/fuel ratio, so it ends up guessing. Your car performs poorly and uses more fuel than it needs to.

-Sourced from howstuffworks.com

What is a pre cat or manifold cat?

There are three catalytic converters in our cars. Two of them are located in the exhaust manifolds and the third is located uderneath the car as part of the "Y" pipe. The precats are the ones located in the exhaust manifolds they get hit with the exhaust first and then the third cat under the car cleans up whatever they do not filter out.

Where are the oxygen sensors?

You will find in our cars that there are four oxygen sensors. There are two upstream and two downstream. The upstream ones are located at the top of the exhaust manifolds before the "pre cats" that are built into the stock manifolds, they are known as the "primary O2 sensors". The signals from these are what the ECU uses to determine what adjustments need to be made for the ideal air fuel ratio. These sensors should always be replaced with OEM ones and should never be modified as they play a key role in keeping your engine running healthy.

The "downstream" oxygen sensors or "secondary" oxygen sensors are located just after the pre cats. The signals they send to the ECU are used in conjunction with the primary O2 sensors to determine if the pre cats are operating efficiently. They do this by reading the differences between the two sets of sensors. These O2 sensors are not critical to engine performance they are just there for emissions purposes although they should still always be replaced with OEM sensors.

So why do I get a CEL with headers?

The reason the CEL appears with headers is that when you install headers you remove the pre cats when you remove the stock exhaust manifolds. When you do this there is no longer anything filtering in the exhaust stream between your primary and secondary O2 sensors. The ECU then sees the same readings at both the primary and secondary sensors, it then triggers an emissions related CEL because of the lack of filtration. These codes are P0420 (Catalyst System Efficiency Below Threshold (Bank 1) and or P0430 (Catalyst System Efficiency Below Threshold (Bank 2).

Will these codes hurt my car or it's performance?

No, these codes are emissions related and have no bearing on fuel or air delivery to your engine. The only issues are that you cannot pass an OBD2 inspection with them on and if for some reason something else goes wrong with an unrelated part of the engine that may harm your engine, you won't know because the CEL will already be on. If you have no OBD2 inspection and you can pass a visual inspection the only thing you may want to do is periodcally pull the codes from your car to make sure nothing else is wrong in any other areas.


How can I get rid of the CEL?

With some of the older tibs (06 and older) you may not get a CEL with headers because the emissions sytems (ECU and O2 sensors) are not as sensative. If you do, installing a high flow cat under the car and relocating the secondary O2 sensors behind it may get rid of this issue.

If you have an 07-08 the problem is much more of a pain to deal with. There is no chance of not getting a CEL with the 07-08 models. If you add headers on these models you will get a CEL. Getting rid of it is a pain as well. A normal high flow cat will not do the job, the emissions sytems are far too sensitive. You will need to buy a high end cat (random Technologies for instance) and relocate the O2 senosrs behind that and even then its not a guarantee.

The reason for no guarantee is that although those higher end cats may get rid of the ineffiency codes they may give you a code for O2 sensor heated circuit or O2 slow response. The reason for these is because the O2 sensors also signal the ECU as to how fast the cat heats up. If the new cat heats up way out of range that the stock cats would have, the ECU will aslo throw a CEL. The slow response is just as it sounds, a response back to the ECU from the O2 sensor that is slower than what stock would be.

The best bet with an 07-08 is not have headers in a state that does an OBD2 inspection or just be prepared to take them off every year.

Can't I just reset my ECU before inspection?

No, if your state does an OBD2 inspection they will also be checking for incomplete ECU cycles. If there are too many incomplete your car will come back as "not ready for inspection".

What is an ECU cycle?

An ECU goes through many "cycles" after the ECU is reset to "learn" all the perimeters it should set itself at to operate as efficiently and cleanly as possible (maintaining the ideal A/F ratio). Each emissions system (EVAP, O2 sensors etc.) has to see certain driving conditions to be able to set itself, this can take a few hundred miles to complete. For instance in New York State you can only have 1 ECU cycle incomplete in order to be ready for inspection.

Can I use an O2 spacer?

They may work on an 03 or 04 and its hit or miss. On anything newer than that they will not work.

Can I hang my secondary O2's out in fresh air?

Again, maybe on an 03 or 04, anything newer than that and you will get an "O2 sensor inactivity" code.

Are headers legal?

In a short answer no. Federal guidlines mandate that no changes should be made to any emissions systems on any vehicle until that particular part fails. When that part fails, it should be replaced with an OEM equivalent part.

Which bank is which?

The 3 cylinders on the firewall side of the car are known collectively as bank 1, the 3 cylinders toward the front of the car is bank 2.

This write up is to give a quick explaination and understanding of the CEL related issues with our cars and headers. Be sure to check with your local and state laws and regulations regarding inspections to see what your options are.
 
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#7 ·
At first when I saw the thread title, I was like.... OH NO... not Will asking the same damn question too! Then I was pleasently suprised to see a nice descriptive writeup documenting the process. I was even happy to learn a few things in their (about what harmful things are produced by the engine) that I didn't fully know prior.

Thanks man!
Scott
 
#80 ·
i havent gotten to the bottom of this thread yet but there is some great information here and i dont know if anyone has ever heard of them but there are these "fake" sensors that tell teh computer everything is perfect they are called "mil" sensors and they are usually plug and play i had to create my own harness for cars older than 2000 but for my 03 tib they plugged right up they cose about 60-80 bucks a peice and replace the 02 sensor so they tell the computer they are working fine thus deleting the CEl.
 
#16 ·
How can I get rid of the CEL?
With some of the older tibs (06 and older) you may not get a CEL with headers because the emissions sytems (ECU and O2 sensors) are not as sensative. If you do, installing a high flow cat under the car and relocating the secondary O2 sensors behind it may get rid of this issue.

Its hit or miss with your year, but you do have a better chance of getting rin of a CEL or not getting one at all than an 07-08. Try DC sports headers, from what I've read they are more CEL friendly for some reason, plus they fit really well.
 
#25 ·
just a heads up, this is different than the widely used ARK spacer. This is actually a mini cat (obvious from the name lol) and has honeycombing coated with platinum and rhodium in it that might work to solve one of the two problems as will already mentioned. Unfortunately the ARK spacer does not have these honeycombs, it simply takes the O2 sensor out of the direct flow of the exhaust.

you may have already known this i just figured it should be noted.
 
#21 · (Edited)
Well in theory, it would get rid of the catalyst inefficiency code, but then you'd have to worry about the heated O2 sensor codes. I think the best bet is with 2 very small high end cats located in the headers (all runners join to one before the cat). I know it would defeat the purpose of having headers somewhat, but they would still flow better than stock. Plus they would be crazy expensive. There is an answer out there for sure, even for the FL2's, it's just the lack of aftermarket support for the tib. No company is going to go through the R and D for this kind of thing for our cars.

Can't hurt to try that method I guess, the worst thats going to happen is it won't work.
 
#26 · (Edited)
Remember this thread i created

Saw these the other day,
There uber expensive, but would it add horse power ?that be not much but might be a way to have better flow with out the cels for the F/L2 tibs ?

http://cgi.ebay.com/ebaymotors/MagnaFlow-DF-Converter-02-06-Hyun-Kia-2-7-frt-OEM-49273-/180599975538?pt=Motors_Car_Truck_Parts_Accessories&fits=Model%3ATiburon&hash=item2a0c98ee72

http://cgi.ebay.com/ebaymotors/MagnaFlow-DF-Converter-02-06-Hyun-Kia-2-7-frt-OEM-49273-/180599975538?pt=Motors_Car_Truck_Parts_Accessories&fits=Model%3ATiburon&hash=item2a0c98ee72

They have them just how much you want them cause of the price lol

best bet wou;d be to take some ebay headers ans cut and fab a HF cat to them would be cheaper again is the price woth the gain ?
 
#27 · (Edited)
I hate to add to an older forum and not sure about the technology behind the tib oxygen sensors, but with mustangs and most ford vehicles, you can add a resistor and a capacitor to the oxygen sensor behind the cat, and it will trick the ecu to thinking it is reading correctly. I did this on a contour after the cat failed and I gutted it. May not pass emissions test but it does get rid of the CEL.

http://www.contour.org/ceg-vb/showthread.php?760-Mileliminator(s)-installation&

Look at the second post, very simple to build your own, again I don't know if it works with the tiburon just some insight to try if your cel is on because of your oxygen sensor or no cat.
 
#28 ·
Ok, with this in mind, On my 04gt i was told that rewiring the front o2 sensors to the rear catalytic converter, via solder and extended wiring, would prevent the CEL from popping up. Also, would using a Apexi neo or other piggyback AFR program in conjunction with a wideband O2 sensor still trip the CEL? Given the fact that they alter the A/F that goes into the engine to create optimum performance. Another question, Say I go to a performance exhaust shop and have them run a custom cat back exhaust, utilizing 2.5" pipes, and say borla mufflers, will that be suitable enough to keep the CEL from activation via your info on the 03-04 tibby. thanks.
 
#29 ·
Catback has nothing to do with a CEL, so do whatever you want there. Your Primary O2's control your cars A/F ratio, do not touch them, relocating them will not help anyway because your ECU needs to read a difference between the primary and secondary o2 sensors. So try to move them around all you want, but if there's nothing filtering in between the 2 sets, it wont help the CEL issue. As far as tuner changing the A/F ratio via the primary o2's, again, you need to have a difference between the 2 sets, with the proper heat cycling, response time, etc.
 
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