legacycentral bbs

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?

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.

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?

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.

Turbo cars dont need O2 correct??

Why would it matter whether it was turbocharged or not?

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...

Oh.

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

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..

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.

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.

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

Sounds more IAC or tune-up related.

Steve

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

OK, thanks a lot vrg3

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..

Oh.

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