Renix 02 larger influence on idle than originally thought.

Changed my Renix 02 yesterday because my fuel mileage has been getting bad. The "idle hunting" that I have assumed to be Renix nature went away. Idles very strong and consistent without the occassional drop in idle speed that many of us are familiar with.

This is important to me because we've all wondered how to tell if/when the system is in closed/open loop mode? As a heated 02, Renix apparently uses the 02 signal ASAP so if you're experiencing good idle frequented by a dip in idle speed, might start looking into a new 02?

I'll bet a lot of Renix' owners are running around with bad O2 sensors. I replaced mine a few weeks ago, because of sooty exhaust. It ran OK, just very rich, and of course the MPG suffered.

The O2 sensor is very easy to test with a multimeter. The O2 wiring feeds right next to the FPR, so it's easy to reach.

You can also hear the O2 sensor switching at the exhaust pipe, if you have a good ear. It'll switch once every second, and you can hear a difference in the exhaust tone, even though the RPMs remain the same.....

Not trying to flame you here, but I think it's the pipe you hear clicking.....O2 Sensors only produce a varying voltage to the ECU, they are not a relay, nor do they have any mechanical parts that make contact and produce a click. Here is a good write-up on how an O2 sensor works........http://hostingprod.com/@aa1car.com/library/o2sensor.htm.

Hi Chasjr1, welcome to the board. :wave:

Our older Renix equipped XJs utilized a Titania type O2 sensor, rather than the newer Zirconia types. You're right about the Zirconias, and that's a good web page on them.

The Titanias switch from 0v to 5v, [EDIT-SHOULD READ 0-5V, RATHER THAN 0-1V] once every second, to regulate the injector pulses. When I replaced my O2 sensor, I had a voltmeter attached to the O2 signal wire, so I could watch the pulsing voltage. I went around to the rear of the vehicle at the exhaust pipe, and I could hear the 1 hertz pulsing from the O2 signal. Granted, you have to listen closely, and know what to listen for, but there's a definite change in exhaust "tone", at a frequency of once per second, that correlates with the voltmeter movement. (I know, it surprised me too......)
Titania O2 sensor

Chasjr1 said:

Not trying to flame you here, but I think it's the pipe you hear clicking.....O2 Sensors only produce a varying voltage to the ECU, they are not a relay, nor do they have any mechanical parts that make contact and produce a click. Here is a good write-up on how an O2 sensor works........http://hostingprod.com/@aa1car.com/library/o2sensor.htm.

Click to expand...

I can understand how the 02 in closed-loop idle may make subtle exhaust note changes and it may even promote good enough CAT operation to generate ticking sounds (expansion/contraction) from the CAT. But the sensor itself doesn't have any type of relay contacts that would be audible on it's own.

I understand Renix to be a 0-5Vdc 02 sensor so a volt meter should able to measure operation fairly easily. Before doing all that however I realized my poor mileage AND somewhat erratic idle coupled with the knowledge that the old 02 was over 4 years old. $52 later for the Bosch and now I worry the trip meter is broken between fill-ups while idle is rock-solid.

One of those things that happened so gradually, I just got used to it until fuel costs started going-up and with a well-adjusted TPS plus good IAC, idle hadn't been bad enough to warrant concern. But, it is interesting that with a weak 02 it would more freqently drop and recover idle after coming to a stop. Apparently, that may have been the open-loop mode switching in/out or simply how it operates in open-loop mode with no 02 input?

Too bad Renix has to be so damned tight-lip'd about what it's doing but for little more than the cost of a fill-up, it was easy enough to solve in this case.

Runnin'OnEmpty said:

Hi Chasjr1, welcome to the board. :wave:

Our older Renix equipped XJs utilized a Titania type O2 sensor, rather than the newer Zirconia types. You're right about the Zirconias, and that's a good web page on them.

The Titanias switch from 0v to 1v, once every second, to regulate the injector pulses. When I replaced my O2 sensor, I had a voltmeter attached to the O2 signal wire, so I could watch the pulsing voltage. I went around to the rear of the vehicle at the exhaust pipe, and I could hear the 1 hertz pulsing from the O2 signal. Granted, you have to listen closely, and know what to listen for, but there's a definite change in exhaust "tone", at a frequency of once per second, that correlates with the voltmeter movement. (I know, it surprised me too......)
Titania O2 sensor

Click to expand...

Hey, thanks for more good stuff! I think we're a little confused about this type of voltage operation for the Titania Lamdba sensor. This graph indicates the 0-5V operation scale and that is what I've heard before about Renix 02:



Along with this description:
The operating principle of a titania lambda sensor is entirely different from that of a zirconium lambda sensor. A titania lambda sensor works like a coolant sensor. It changes resistance as the air/fuel ratio goes from rich to lean. But instead of a gradual change, it switches very quickly from low resistance (less than 1000 Ohms) when the mixture is rich to high resistance (over 20,000 Ohms) when the mixture is lean.

The engine computer supplies a base reference voltage of approximately one volt to the titania sensor, and then reads the voltage flowing through the sensor to monitor the air/fuel ratio. When the fuel mixture is rich, the resistance in a titania oxygen sensor is low and the sensor's voltage signal is high. When the fuel mixture is lean, resistance shoots up and the voltage signal drops.

Based on this graph the 1 cycle per second or 1Hz is correct and I'm sure some type of audible signal can be detected. Whether that is noise within exhaust system (expansion/contraction) or simply mixture change of the combustion, I just don't know but it's good stuff to think about.

Just to clarify guys, what I heard was indeed a change in the exhaust tone, obviously not a 'clicking' of the sensor itself.

It sounded like this: BURBLE, burble, BURBLE, burble, BURBLE, burble, etc., at exactly one hertz/cycle per second.

XJXJ, yeah, too bad the Renix didn't have a CEL, to tell us when the O2 sensor goes bad. I had the same experience as you; one day I noticed a sooty exhaust, and wondered why........?

OOPS, I mis-spoke, it's indeed a 0v-5v switching on the Titania , instead of 0-1v. :laugh3: