headers and obdII

[Camel]

NISTECH - Can you install a hotshot header on a 98 240sx (obdII) and avoid getting constant CEL's?

If so, can you reccomend a procedure and set of parts that will be needed to do so?

Also, the factory cat would have to be replaced. What would be your recommendation on an aftermarket cat?

Thanks.

[NISTECH]

If it has the o2 port you should be ok. as far as a cat goes. one that mounts at the header flange should still perform as the original one did. but there is another problem with adding that equipment. your states smog laws. here in california it is illegal to install that header if the car will be registered for use on the road. you may experiance egr codes if the back pressure in the exhuast is droped to much since the bpt wont close of the vent with lack of back pressure. we are talking about a factory backpressure of about 2 psi. so you dont have much room to play with. I have not heard to many complaints of check engine lights here on the boards with the guys using them so again you might be ok its just smog laws you gotta check in your state.

[Camel]

thanks for the reply, headers are legal in my state, i just have to pass the sniff test and have no cel's.

[LiU]

NISTECH:can you help me w/ my problem? I'm running HS headers on a 96, I relocated the 2nd O2 sensor behind the cat (original cat, although it was not a shell, it was a cat), yet I still get a CEL, I've reset it several times and I still get a CEL - any ideas what I might be missing? Thanks!

Camel: has methodchris replie to you yet? not to me heh, seems like he's not too big of a forum freak

[NISTECH]

your other cat may be to far back and not getting hot enough to work with in the 25% limit. the o2 fluctuations(sweeps) can not be within 75% of each other. meaning the rear o2's sweep can not be with in 75% equal to the front o2's sweep. that rear cat is so far back it is not getting hot enough to perform the proper thermal reaction. U really should get the cat right up to the header flange. and have a machine shop fab in pipe thread behind it in the pipe.

[LiU]

NISTECH:I just checked, the cat is immedaitely behind the header, and the relocated O2 sensor is about 2 in. behind the cat. both sensors are Bosch universal sensors, I dunno if that contributes to the CEL (I've heard some ppl say only Nissan sensors should be used, but I cannot confirm this). There is some1 (methodchris) that runs the same basic set up w/ HS header as me and is not getting a CEL, so I have contacted him, waiting for a reply.

thanks!

[Camel]

The HS header goes from the block all the way to the fake cat location under thwe driver's seat. There really is no way to get the cat closer to the head. Could he/I get a newer cat and expect better results from the o2 sensor array?

[NISTECH]

that cat may only be an oxidizing cat and not a reduction cat. the reduction cat seperates oxygen in the nox molocules and uses those oxygen molocules in the oxidizing cat to add to the hc and co to create h2o and co2. if that cat is not getting hot enough or does not have enough oxygen to do its job you will get a cat effenciency code(po420) you may need to up grade that cat to a TWC cat.

[LiU]

so from running a CEL check, the code should be 420? alright thanks alot, I'mg oing to autozone when I get the chance to check the code, if it says 420, that means a random tech ot catco cat should suffice?

[NISTECH]

random tech ot catco cat

???? what is that

[LiU]

oops sorry but I was asking if a random technology's high flow cat or a catco cat would work in eliminating the CEL since I believe both cats work w/o a precat (like the stock cat I have right now)

[NISTECH]

just as long as its a TWC you are ok. That cat takes care of all three pollutant gases since its forward bed is the reduction cat and will generate the oxygen needed for the oxidiztion bed. your old set up either had the reduction at the maniold and the OC cat at the rear. or the first cat was a twc which did both and the other cat was clean up of any remaining. but since the car does not have any sort of air induction you cant soley run an OC . any twc should work.

[LiU]

sorry but can you clarify what is a TWC vs. OC? thanks again.

[NISTECH]

oh sorry man..Three Way Cat(TWC) Oxidizing Cat(OC)

TWC does all 3 major pollutants and the OC only does HC and CO

[LiU]

cool thanks alot. looks like I will bel ooking into a catco high flow cat.

[Camel]

that will probably solve our issue with cel's and headers. this is one for the archives. thanks for the cat lesson nistech.

[s14db]

What about the fake out boxes you can buy to replace the rear o2? They plug in place of the second O2 sensor and put out a fake signal. All the engine managment is done from the front O2 and the rear is just a emmisons reference.

[Camel]

The Random Technology HF cat worked once i welded in an o2 bung behind the brick for the rear o2 sensor. Just wanted to update the thread with useful info. So the setup is Header/RT CAT with o2 bung/apexi catback = no cel's.