Bleakened

I have an automatic 98 DX hatch and after I bought it, I found out that they took the stock headers and cat out and put in some unknown aftermarket headers with a straight pipe. They also left me with neither o2 sensor but I have since bought both to put in.

The problem is: i get misfires with just the pre-cat one in and the post-cat won't fit due to another part in the way of the bung where it screws in. One mechanic recommended I put stock headers/cat back on (they're put in as 1 piece) and the other said I can do it cheaper by creating a new bung on the pipe that won't be blocked.

My question is... If I do it the cheaper way and weld on a new bung, will not having a cat throw off the post-cat o2? or will it not effect the o2's readings? I have read that the post-cat o2 doesn't affect the air/fuel mix and is only there to monitor the catalytic converter.

If this were true, why would my car misfire only when the pre-cat is installed?

I just want some better MPG as it is my daily driver!
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TL;DR, will the removal of the catalytic converter make the post-cat o2 send wrong signals?

Bleakened

Anyone? Maybe? Nobody knows why my car only misfires with the first o2 in. It runs fine without!

belairbrian

The second o2 sensor is there to determine catalytic converter efficiency, so not having a cat will definitely have an effect.

What makes you believe the o2 sensor(s) are causing the misfire? CEL should be on, What codes are you getting?

Bleakened

I'm getting codes for random/multiple misfire on all 4 cylinders. I have already tested plugs, wires, vacuum lines, IAC, new injectors, distributor cap and more.

The only thing that throws those codes for misfire is when I have the pre-cat sensor in. When I take it out, it runs very smooth and no codes (except the missing post-cat o2)

That's why I'm wondering if the 2nd o2 will even help before I waste money on a new cat.

But you said a missing cat will affect it so I should replace my test pipe with a real cat, right? or should I not?

Bleakened

Anyone?

JRCivic1

So if you are saying that the car runs fine without a primary O2 sensor, but if you plug in the primary O2 sensor, the car runs poorly and you get misfire codes... sounds like the O2 sensor is reporting faulty values to the ECU. Is this a BRAND NEW HONDA O2 sensor ???

Did you replace the computer when you plugged in the primary O2 sensor ???

What codes do you have when the O2 sensors are unplugged ???

Bleakened

I get 6 codes with o2 plugged in, 1 for multiple/random misfires, 1 for each cylinder and 1 for missing o2.
I get 2 codes with no o2 plugged in, 1 for each missing o2.

Yeah, the o2's were brand new from Autozone. The ECU is the same stock one. My mechanic says if I put in a cat and ditch the straight pipe everything will work perfectly with both o2's in.

So my question is now... can someone find me a catalytic converter that will fit my exhaust? I have some kind of aftermarket **** going on but nobody recognizes its brand or anything. It's all aftermarket from headers down except the muffler.

I can provide pics of the whole thing if needed

gzes

Damn if you were flose i have everything you need... But i would get a high flow cat. I have both im gonna scrao since im not gonna run them in my sol. Just gonna tune out the o2 sensor readings