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Hey guys! First time poster here.

So I purchased a 99 civic lx a while back and ended up replacing the exhaust with a headers/back system. I ended up having to purchase a universal o2 sensor for the secondary o2 since the oem one would not reach. The car was (obviously) throwing a code for the rear o2, and after hooking up the new o2, I got it to clear, but only for a short time. The car started sputtering/hiccuping when warmed up at roughly 2000 ish rpm's while accelerating. It feels as if it's getting too much fuel/running rich, but when I pulled the plugs they have a bit of white on them as if it's running lean. It's also getting poor mileage when being compared to before the issues. Anywho, I tried the spark plug fouler trick and couldn't get enough clearance to get them in, so I just ordered an L-shaped o2 spacer last night. My question is, will getting the ecu to read with the o2 correctly possibly fix my problem with the car hesitating, or would it most likely be a separate problem entirely?

Thanks a ton in advance guys! I'm really getting frustrated with this issue .

 
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As a test, I'd disconnect both O2 sensors and give it a test drive. If the poor running is gone (or a whole lot better), then it's probably caused by the aftermarket primary sensor.


I'd get rid of the universal sensor and put the correct sensor in it (DENSO or NTK, whichever came in it from the factory). The wiring harness may need to be modified/extended to make it work......but I sure wouldn't use anything but the OEM part.

 
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First off, thanks for the fast reply!

So I just tried as you suggested and disconnected the primary/upstream o2 and it ran just fine! Just to be clear, I am still running the stock/oem o2 but perhaps it was damaged when installing the new headers? Anyway, I guess I'll be ordering a new OEM upstream sensor. Hopefully that's all it is (fingers crossed).

 
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Oh, I guess I misread that...

Try driving with only one sensor disconnected at a time then, see which one makes it run poorly.

I still suspect the primary sensor is the flaky one though, especially if it is original. I've seen them stick at low or high voltage long enough to cause misfueling and poor running, but not stick long enough to set a code for the sensor itself.

 
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So after driving a bit more the car began to run poorly again. Just as bad, if not worse, than before. I went to a local auto parts store and several of the guys there offered their advice. They said that, by splicing in an aftermarket o2 for the secondary o2, it is telling my ecu that it is running on 2 primary's. He said they are "battling each other", one telling it to run rich, the other telling it to run lean, therefore causing the sputter and making it run poorly. He wouldn't sell me a primary o2 because he said I need to first get the secondary hooked up with an already wired o2 that has a plug and play capability.

They also mentioned that I need to get an aftermarket intake system for my car since I'm still running stock. He said it needs more air going in so it doesn't continue to dump a lot of fuel...

So I guess I'll wait for my l-shaped o2 spacer and in the meantime research for the correct secondary o2. I need one that will reach my aftermarket downstream o2. Any suggestions??

Thanks again to any who respond and offer their wisdom!

 
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With the O2 sensors both disconnected?
Only one connected? Which one?
Both connected?
Explain more






Oh...THAT was a good laugh...I'm crying over here..

There's a reason those people are there, and not actually fixing cars.

Does this not have a cat at all?

 
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Oops, I should have been more clear! I originally tried running it with only the primary connected and that's when it was running like garbage. After reading your post, I had the secondary connected but tried running it without the primary plugged in. It ran well for a little while, then started doing the same thing .



LOL. I don't know too much about the mechanical stuff with cars and even I was like "Wha?" lol.


No cat, just headers, test pipe, etc.

 
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Ok so how does it run if you leave both O2 sensors disconnected?



It hurt my brain.

*hugs a tree*

This makes it tough to decide if the rear sensor has much to do with how it runs or not. The computer can still control fuel delivery based on the rear sensor input -- at certain times.

 
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Sorry for the late reply! So far I've tried: disconnecting the primary o2, leaving the secondary connected; disconnecting the secondary leaving the primary connected; and disconnecting both o2's. Same thing each time: runs fine for about 5-10 mins then starts hiccuping/sputtering at around 2000 ish rpm's. If I beat on it a bit, it clears out and runs better for a bit, then the same thing happens again. It feels as if it's getting carboned up or backed up. I can relate it to a 2-stoke dirt bike with a dirty/fouled out spark plug. You can clear it out, but then it carbons up again...

Anywho, I am having my dad take it in to his work tomorrow. One of the techs said he'll take a look at it. It's getting frustrating .

 
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Sounds like it's time to dig a bit deeper. I'd be grabbing my scanners first, checking live data when it acts up, and probably take a "movie" of the data action.

 
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Good idea. I'll see what the tech says tomorrow and go from there. Thanks .

 
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Yeah, you have pretty much ruled out the O2 sensors now......time to see what else happens at that 5-10 minute area to make it run bad.

Hope it's something easy to "see" like a coolant temp sensor reading very wrong values during warmup.

 
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Well, it's all good now! Turns out it WAS the secondary o2. I'll admit, I had it wired incorrectly . A boneheaded move on my part lol.

Thanks again for the help!

 
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This thread is receiving an unfortunate bump .

So, the car was running fine, and now it's doing the SAME thing again. However, I noticed two things: 1.) it takes a lot longer for it to start doing it. 2.) It doesn't sputter as much as before. Also, the check engine light is not on now.

I was considering trying to fun some injector cleaner through it... anyone think it could be dirty/clogged up injectors from running it too rich?

 
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Your mechanic isn't done with it, it isn't fixed. The sensor wiring might have been a problem, but the car still has a problem.


No.

 
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Good point. I'll be giving the guy a call tomorrow. We'll get this darn thing figured out eventually .