bigjdog84

This isnt concerning my civic, but my prelude. Since the prelude forum dosnt get much traffic I figured i'd ask you fellows

I just installed my headers today, and gutted my cat (probably will regret it later, but oh well.). Everything went OK, had quite a few rusted bolts on the cat, but I dropped that along w/the collector. On my prelude there are 2 o2 sensors right in the primary tubes.

So I go to start the car up. It stumbles and starts up struggling a bit. Check engine light is on. Its idling pretty low, the check engine light dosnt go off. I press on the gas a little bit, it stumbles quite a bit then revs. I havent taken it for a test drive, cause I really dont want to, since the check engine light is on.

I'm thinking its the connections to the o2 sensors? Or maybe the gutted cat (unlikely).

Any input is appreciated.
Later/joe

bigjdog84

Btw, this is on an 88 Prelude 4ws Si.

maestro5050

Yes it IS the gutted cat. You have an ODB2 compliant car. Essentially your first O2 sensor reads the exhaust as it comes out of the engine. This is the raw and uncleaned form. The second O2 reads the same exhaust AFTER it has passed through the cat and been cleaned up. The second O2 tells the ECU if the exhaust has or hasn't been cleaned and then allows the ECU to adjust fuel maps, etc, to correct problems.

As far as I have seen, the second O2 will not throw a CEL so long as it reads the exhaust as being cleaner, barely cleaner or totally cleaned makes no real difference to it. But if it is the same, you will get CELs all day long and have a hell of a time trying to correct it.

You really have three options at this point:

1) Put the cat back together or install a high flow cat.

2) Splice the wire to decrease the signal/reading of the O2 sensor. (Note: I have never tried this and don't know how to do it or how it works. I have just heard there is something like this you can do in this case.)

3) Weld the hole shut or find a bolt that will thread into the spot where the O2 sensor goes. DO NOT DISCONNECT THE O2 SENSOR. Just wrap it in a few layers of foil, then some plastic to protect it from water, and zip tie it to something underneath the car.

With the third option, the O2 will read its own heat and see that the exhaust is "fully cleaned." It should then leave your ECU and fuel maps alone and let you go on as normal. I know this works because I put a test pipe on mine two years ago and zip tied the fugger up there and haven't had a problem since then. But remember if you do have a problem that would normally be automatically corrected by the second O2 sensor, you will have to diagnos and correct the issue yourself.

Good luck to you and hope this helps.

Edit: You posted the year and model while I was typing up this response. The information listed above may not apply at all to your vehicle. I was thinking it was a late 90s Prelude.

bigjdog84

Yeah, mines an 88, its an older model with two o2 sensors in the primaries. I'm not sure why theres 2 there, one is green and one is white. I doubt thats the problem since there is no o2 after or at the cat. Nice try though :thumbup:

Bakeoff

I've worked on my buddy's 89 Si a ton. Pull back the carpet and see what code it's throwing. Could just be that you knocked a connection loose, didn't get one of the clips tight, etc. Hit me up if you need help. I've worked on far too many b20a5's that I care to remember.