obx header installed and check engine light on

[yoinkAzenki]

i searched but couldnt find any straight answers so sorry if this has been covered. i just installed an obx header on my obd1 95 s14 ka24de and after driving around my check engine light came on. the car runs fine but the problem is that i have another o2 sensor fitting on the bottom of the header which is bigger than the stock fitting so my second o2 sensor won't fit. i decided to use an old o2 sensor that fits on the top of the header to plug up the bottom fitting. then i just plugged my second o2 sensor on but just left it hanging. so im guessing this is what made the cel go on. i pulled 3 codes from the ecu: 25 - Idle Air Control Valve, 35 - Exhaust Gas (EGR) Temperature sensor, 77 - Rear O2 sensor. after cleaning up the iacv i decided to erase the codes and the car still runs fiine. i know the rear o2 sensor is for diagnostic purposes but i wanted to know if its ok to run the car without the rear o2 sensor not properly installed? is there a 3 wire o2 sensor that will fit the bottom fitting of the header? i know the sr uses a 3 wire o2 sensor that will fit but is it the same as the rear o2 sensor because they look different at the tips? isnt the rear o2 sensor also the exhaust temp sensor? sorry for all the questions but any input would help i just want to make sure my car is running right.

[ChingSR20]

I have the same headers had them for over a year now and the car is still running strong.

[The Chad]

You can buy threaded bungs for this, or just have an exhaust shop weld one in for you that will allow the O2 sensor to fit snug, That is what i did for my Hotshot header. The second thing you will run into is that it will be reading without a primary Catalyst, so it will read more air than it should. My buddy just welded on an extra long bung to limit the air flow past the sensor...it seems to be working fine...still runs like a champ. let me know if you come up with an alternate solution.

[yoinkAzenki]

ok ill see if i can get another fitting welded on so i can put the second o2 sensor on. but i still want to know if its ok to run the car without the rear o2 sensor not properly installed? is there a 3 wire o2 sensor that will fit the bottom fitting of the header? is the rear o2 sensor also the exhaust temp sensor?

[hunter8411]

The rear o2 Sensor(3 wire) is just for Emissions. I have had mine unplugged all together for a while and it runs fine. The only issue is the CEL is on.

[yoinkAzenki]

Originally Posted by hunter8411

The rear o2 Sensor(3 wire) is just for Emissions. I have had mine unplugged all together for a while and it runs fine. The only issue is the CEL is on.

if i dont want a cel is there a universal 3 wire o2 sensor that will fit on the bottom of the header? is there a difference between the front and rear o2 sensor other than number or wires and size?

[S14Tech]

So i had the exact same problem for the first half a year i had my car. I just used a front 02 sensor in the rear position and i managed to hook it to the wiring harness (it just plugged in!). It was a bosch that i picked up from advanced auto. The light didnt go away immediately, but about 2-3 days later the cel went away. Hope that helps

[Dream240]

Originally Posted by hunter8411

The rear o2 Sensor(3 wire) is just for Emissions. I have had mine unplugged all together for a while and it runs fine. The only issue is the CEL is on.

Yeah it's just for that little thing called emissions that some stupid EPA guy came up with in his garage one day.

Gimme a break. First of all the oxygen sensors are hooked into your emissions system which is in turn hooked into pretty much every other aspect of your cars performance. Now unless you've got a custom tuned ECU and fuel management, then you're running your engine out of A/F spec, thus hurting performance, MPG, and the life of your head (no the other one).

Unfortunately the 95' 240 has a hybrid mix of emissions stuff in it. You can still do the OBD-I diagnostic but you've got more items involved in throwing codes than the S13.

If you leave your 2nd O2 unplugged the computer will assume the error is your CAT or the O2 sensor and start to lean out your mixture to assure that you're not going to pollute the air too much until you get the problem fixed. The too lean mixture can damage your head in the long run. And you're losing power.

What you need to do is get a bung welded in place AFTER your secondary cat, basically in the exhaust piping. THEN get an aftermarket cat that will bolt up to space where your secondary "fake" cat is. That way you'll have an O2 sensor BEFORE AND AFTER a real cat. Then the light will shut off and you will pass smog too, at least the sniffer test.

Or you can just say 'fuck it', and unplug your CEL light bulb in the dash. But if you do this you might as well shoot yourself in the face cause you definitely don't belong anywhere near a modified car.

Oh and your EGR temp. sensor is not the O2 sensor. That's a whole different diagnostic.

[projectRDM]

Dream, I hate to prove you wrong, but here goes:

The secondary oxygen sensor is used for OBD monitoring only. It has no effect on the A/Fs or engine operation. None. It's only purpose is to verify the catalytic converter is properly working. The ECU's tune is not sophisticated enough to alter the A/Fs in lieu of a missing or faulty converter.

To correct this and eliminate a CEL, you have to have a functional converter somewhere in the exhaust stream, usually placed after the aftermarket header, replacing the OE resonator, and then weld a bung in the rear flanged portion and place the rear O2 sensor there. Putting it anywhere else in the exhaust will not see a significant change and the CEL will continue to read a code.

And all this info about header/cat solutions was known 12 years ago. You guys really need to do some reading. Hell, even Sport Compact Car did an article on a Hotshot header install and the issues with the O2.

[Dream240]

huh. Well here's the page from the FSM. I misunderstood the definition.



The last sentence clearly states that it's diagnostic only. It's different for the OBD-II 96-98 right? At least that how I understood it waaay back when I installed my old hotshot headers on my 96. I had to do the whole bung-relocate 2nd O2 sensor crap to get the light to turn off.

Oh yeah and like he said, this whole install/mod HAS been since years past. I'm sure there's info on Zilvia somewhere explaining the scenario.

Thanks Russ.

[yoinkAzenki]

ok after reading all the replies and doing more research i think i know what to do. as of right now my rear o2 sensor is plugged into the harness but since its too small to fit into the bung on the header i left it hanging and i just put an old front o2 sensor ,since it fits, into the bung to seal it up. after doing this i dont have a cel and the car runs fine. i know the fsm saids "the rear oxygen sensor is not directly used to control the engine system..." but my question is: is it ok for me to run the car like this?

[aznpoopy]

what you should do is get a new bung installed so you can put it in, or get a reducer so it will fit

read russ's response. yes its fine. it just throws a cel.

[yoinkAzenki]

Originally Posted by aznpoopy

what you should do is get a new bung installed so you can put it in, or get a reducer so it will fit

read russ's response. yes its fine. it just throws a cel.

ok so ill have to get a cat and have a bung welded on after the cat and thats where i put my rear o2 sensor. before i do that i found out that my bros sr20det o2 sensor fits the rear bung on my header and its also a 3 wire so it fits my harness. if i use this will it work or does it operate differently than my oem rear o2 sensor?

[projectRDM]

It will work fine.


To clarify, all S14s have this issue, however the 95-96 models use the smaller pitch 3wire sensor while the 97-98s use a larger (OE size) sensor, but with 4wires. It's not a matter of OBD-I vs. OBD-II, they're all mandated due to the close coupled catalytic converter.

[The Chad]

Well i suppose i was a tad innacurate. Looks like two people may have learned something from this thread. Thanks again fellow Zilvians!

[projectRDM]

Originally Posted by murphy

^ word 4 wire is a heated 02 sensor

everything russ has said is right. the 2nd just really measures efficiency

1st well on closed loop don't do a damn thing besides fine tune your AF's

wait... russ said it doesn't fine tune? b.s. all sensors like coolant temp etc on closed loop tell set it and the 02 fine tunes it

unless you meant that the 2nd doesn't set the af's

Correct. The primary O2 sensor fine tunes, not the secondary. That's what the discussion was about. We all know (or should) the primary's function.

And actually, a 3wire is heated as well. All 96-98 models use a 3wire heated sensor for the primary as well, as do *some* 95 automatic models. The single wire sensors are of course not heated.

[yoinkAzenki]

ok that clears up a lot of things. so basically its ok to:
1. run with second o2 sensor not plugged in but will throw a cel
2. have the second o2 sensor plugged into the harness but not into the header since it doesnt fit, which is what im doing and hasnt thrown a cel yet
3. run a primary 3 wire o2 sensor in the rear bung, which fits but might throw a cel