So why again do I need an o2 sensor?

aspect · Post by **aspect** » Sun Aug 29, 2004 2:00 am

I've been having some weird hesitation issues over the past couple days, so I decided to do some tweaking today. Dropped in a new set of NGK plugs, worked like a hot damn, although the idle was still a touch off. So, I decided to unplug the o2 to see if that was creating a problem as well.

Sure enough, idle is better, and the engine seems like it's pulling harder with the o2 disconnected.

My question is, if my car runs so well with no o2 sensor attached, why exactly do I need to replace it?

The sensor is about 6 months old and is a 4 wire which has been very well soldered to the original 3-wire connector. It's quite likely that my recent atmospheric BOV-ing has contributed to the sensor fouling, but it still seems a bit premature for failure.

Anyways, what do you guys think? VRG3, care to explain why I should just go get a replacement?

vrg3 · Post by **vrg3** » Sun Aug 29, 2004 2:09 am

Your car runs better without the sensor probably because your sensor is bad or contaminated. I don't know why such a young sensor would be bad though. Is it possible that there's a problem with the wiring?

Without the sensor, the ECU doesn't run the engine at 100%. Timing is conservative and of course there are no fuel trims. A properly functioning oxygen sensor should improve power, fuel economy, and emissions.

But if you don't want to, you don't have to replace it. Matt's run his car for like a year and a half without a functioning oxygen sensor. And my car passed Virginia's emissions inspection with flying colors (most of the pollutant levels were below the instruments' precision) without an oxygen sensor. A lot of people using EJ22s in airplanes also don't use the oxygen sensor.

aspect · Post by **aspect** » Sun Aug 29, 2004 2:27 am

Hrm...well thanks for the info. I'll try to do a solid butt-dyno comparison later on (zipping around the neighbourhood and looking at the tach for a few seconds while idling doesn't really make for a scientific result).

I'm not really eager to 1) drop another $100 on a sensor, and 2) figure out a way to do another 4-wire, as the oem connector has basically no wire slack left.

I guess there's no way to clean the sensor housing out?

vrg3 · Post by **vrg3** » Sun Aug 29, 2004 2:41 am

I've heard before that you can clean the sensor out by somehow running a lean mixture for a while, but I don't know how you'd do that or if it even works.

Actually, if the only "symptom" is a weird idle, maybe the problem is just that the sensor is further downstream than it's supposed to be. The feedback loop includes more temporal lag than usual.

turbonator · Post by **turbonator** » Sun Aug 29, 2004 8:58 pm

Turbo cars dont need O2 correct??

vrg3 · Post by **vrg3** » Sun Aug 29, 2004 10:16 pm

Why would it matter whether it was turbocharged or not?

aspect · Post by **aspect** » Sun Aug 29, 2004 11:08 pm

vrg3 wrote:I've heard before that you can clean the sensor out by somehow running a lean mixture for a while, but I don't know how you'd do that or if it even works.

Actually, if the only "symptom" is a weird idle, maybe the problem is just that the sensor is further downstream than it's supposed to be. The feedback loop includes more temporal lag than usual.

That's a good point...it almost seems like a time issue! It will rev up, drop, rev up, drop....only while cold though. Usually right after I start it.

My O2 is basically in the same spot as stock...the only change is the flow of gas around it due to the much larger aftermarked downpipe...

vrg3 · Post by **vrg3** » Sun Aug 29, 2004 11:22 pm

Oh.

Well, then, maybe being clogged with carbon is making it slow to react.

turbonator · Post by **turbonator** » Mon Aug 30, 2004 1:20 am

vrg3 wrote:Why would it matter whether it was turbocharged or not?

I read that in makes the car run lean..

http://www.e30tech.com/forum/viewtopic. ... or&start=0 So lean is better for turbo? Excuse my newbness..

vrg3 · Post by **vrg3** » Mon Aug 30, 2004 1:41 am

What makes the car run lean? The sensor? The turbo?

Any engine (turbo or not) needs to run somewhat rich when under high load. Since turbocharged engines can achieve higher loads than naturally aspirated ones, they need to run richer. But that doesn't have much to do with the oxygen sensor, since the engine computer knows what to do.

The sensor is used primarily just at idle and cruise, to help the ECU maintain an air/fuel ratio around stoichiometric. At idle and cruise turbo and non-turbo engines are pretty much the same.

BAC5.2 · Post by **BAC5.2** » Mon Aug 30, 2004 3:10 am

Well, my O2 sensor is damn near the middle of my exhaust, and I still get 24mpg on the highway. It's also dirty as a mother.

I wonder how that compares to you other guys.

Ruby the Sooby · Post by **Ruby the Sooby** » Mon Aug 30, 2004 3:40 am

Hey guys,

I'm curious as to the O2 sensor is to blame for this problem I've been having lately.
When I start my '91 when the engine is warm, I get a really messed up idle. It will drop to around 100rpm, almost stall, then pop up to around 600rpm, then back down, up, down... It seems like it's trying to find the right idle speed, but, like vrg3 said, there's some lag in the feedback loop. But if I put it up to 2,000rpm, and then let it idle again it gets a nice smooth idle going.

So is this from my sensor? and what should I do about it? clean it, move it, remove it?

Thanks guys

evolutionmovement · Post by **evolutionmovement** » Mon Aug 30, 2004 7:24 am

Sounds more IAC or tune-up related.

Steve

vrg3 · Post by **vrg3** » Mon Aug 30, 2004 1:05 pm

Ruby, I'd first look for vacuum leaks with starting fluid. I described the procedure in this thread:

http://bbs.legacycentral.org/viewtopic. ... 7443#37443

Ruby the Sooby · Post by **Ruby the Sooby** » Tue Aug 31, 2004 12:11 am

OK, thanks a lot vrg3

turbonator · Post by **turbonator** » Tue Aug 31, 2004 2:48 am

vrg3 wrote:What makes the car run lean? The sensor? The turbo?

Any engine (turbo or not) needs to run somewhat rich when under high load. Since turbocharged engines can achieve higher loads than naturally aspirated ones, they need to run richer. But that doesn't have much to do with the oxygen sensor, since the engine computer knows what to do.

The sensor is used primarily just at idle and cruise, to help the ECU maintain an air/fuel ratio around stoichiometric. At idle and cruise turbo and non-turbo engines are pretty much the same.

When you remove the sensor it makes the car run lean.. Sry..

vrg3 · Post by **vrg3** » Tue Aug 31, 2004 2:53 am

Oh.

No, the car shouldn't run lean without the sensor unless other sensors or the injectors aren't working right.

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So why again do I need an o2 sensor?

So why again do I need an o2 sensor?