Replacing o2 sensors in a 1990 Q

[mattd1979]

Has anybody here replaced the o2 sensors in they're Qs? If so, were you able to remove them on the engine or did you have to remove the headers first?

Matt

[Q45tech]

Failure to anticipate this problem with periodic applications of antiseize or liquid wrench can cause problems.
I've replaced both O2 at 100k intervals [to achieve near oem switching rates] so I'm on set #3 now at 327k.

Important to observe BOTH the O2 waveform to see min and max and the rate they switch at 2,000 rpm [60 mph].

Nothing like fresh squeaky clean sensors!

[Infinitiguy19]

Wouldn't you heat up the are around O2 sensors to remove them?

If not heat them use a Dextron ATF and Acetone 1:1 mix.

[qship96]

Byron {T3} had no problem removing/replacing both of my original o2 sensors when the Q was almost 12 years old and 203,000 miles........and I noticed zero differences in both mpg and power comparing the old to new.....zero.

[mattd1979]

For some reason my notification didn't work to let me know that others had replied. Anyways, as to Q45tech, I found that out of both 02 sensors, only one was jumping between lean to rich as specified in the manual. The other would operate when the car is first started but then it would go either straight to lean or rich. I can't remember which. They have over 222k on them now so I'd say yeah, they are due for a change. I tried using an 02 crows foot socket to get the sensor to break loose but all that would happen is that the socket would expand and begin to slip like that of an open end wrench on a nut. I was reading a service bulletin on how to replace the o2 sensors in an Infiniti for all models. It mentioned to use wd-40 and let it soak. Work the wrench a little at a time, each time spraying the lube on the threads and then screwing it back down and then back out until it comes out. They then mention to use a thread chaser to clean out the threads and applying anti-seize on them before installing the new sensors. The problem is that I can't get it to budge.
Here is a link to the oxygen sensor service bulletin.
http://x.infinitihelp.com/forum/local_l ... ?catid=216

I can't get a box end wrench up in there because there just isn't enough room for it and have enough leverage to loosen the sensor. The same applies to using a socket and ratchet. Sure, I can cut the harness and if I had a deep enough deepwell socket to fit over the sensor, I still wouldn't have enough room for a standard ratchet to maneuver. That is why, I was wondering if anyone else here has replaced the sensors and if so what was the method that you used?

[Q451990]

I've done it twice... on my old Q and once on the one. No issues on the old Q, but on the current one the sensor was seized. Eventually the threaded bushing that screws into the exhaust screwed out instead, so I had to order a new bushing from IOS. My method was to use the O2 sensor socket and snake extensions up to the top between the back of the engine and the firewall. There may have been a swivel head or wobble head extension involved...

Heath

[mattd1979]

So you didn't have any problems with the socket expanding to the point of slipping on the sensor or was it a very deep socket without the slot in the side? I was going to try to use a deep-well socket but it wasn't deep enough and wouldn't allow for the extension to snap in.

[Q451990]

No, the socket didn't expand and slip, and it's the one with the slot on the side. It came from Advance Auto and cost about $10.

Heath

[mattd1979]

I took some readings with ECUTalk and here is what I got with my original o2 sensors. I notice also that the left sensor seemed to be a little sluggish at the responses as compared to the right sensor.

Right sensor is at 0.20v at 3000rpm
Right sensor then jumps to 0.88v while rpm settles to 2000rpm and then drops back around 0.20v.
Right sensor doesn't move from around 0.20v until engine drops to idle. It then climbs up to and
hangs between 0.79v and 0.85v.
When I accelerate to 3000rpm, the right sensor drops to 0.01v and then climbs to 0.78v.
When I decelerate to idle, the sensor drops to 0.01v and then climbs to and fluctuates between
0.75v-0.83v.

The left sensor is at 0.83 steady at 3000rpm.
left sensor then climbs to 0.86v and then settles down to 0.83v when rpm drops to 2000rpm.
left sensor stays around 0.83v until engine drops to idle. The sensor then drops to 0.01v and
then climbs to 0.84v as rpm drops to idle. It then stays between 0.83v and 0.84v.
When I accelerate to 3000rpm, the left sensor drops to 0.20v and then climbs to 0.84v as 3000rpms
is reached.
When I decelerate to idle, the sensor drops to 0.00v and then climbs to 0.87v at idle.
The right sensor seems to be more active (responsive) then the left sensor.

Right sensor
3000rpm 0.20v
2000rpm 0.20v
idle 0.79v-0.85v

accelerate to 3000rpm : Drops to 0.01v and climbs to 0.78v
Deccelerate to idle : Drops to 0.01v and climbs to 0.75v-0.83v

Left sensor
3000rpm 0.83v steady
2000rpm 0.83v
idle 0.84v

Accelerate to 3000rpm : Drops to 0.20v and climbs to 0.84v
Deccelerate to idle : Drops to 0.00v and climbs to 0.87v.

[Infinitiguy19]

What is there resistance of each O2 sensor when the car is off, Warm and cold?

Should be between 3-1000 OHM's.

Mine are between 7-8 OHM's between the both of them.

[mattd1979]

I took readings of the sensors before I started the car for the day and I took readings again after I got to the house. Here is what I got.

Right o2 sensor cold : 010 ohms
Right o2 sensor hot : 016 ohms

Left o2 sensor cold : 009 ohms
Left o2 sensor hot : 015 ohms

I also too a reading of one of the new sensors, cold of course at 003 ohms.

I also have another question. When your viewing the guages for the o2 sensors on ECUtalk, are the needles suppose to sweep from high to low voltage a certain amount of times every 5 seconds or so or are they suppose to move gradually depending on RPMs?

I know that on other vehicles the voltage is either high or low like on and off, there is no in between.

[Q45tech]

Measuring the [peak or minimum] voltage with a VOM tells you little, what counts are the shape of O2 waveforms [with 0.5 volts as centerline] and the number of cycles [lean -rich-lean] per minute.

The ecu understands anything over 0.55 as rich and anything under 0.45 as lean.

http://autolabscopediagnostics.com/sensors2.html
Look at before [old O2] and after new O2 waveforms.

[mattd1979]

Measuring the [peak or minimum] voltage with a VOM tells you little, what counts are the shape of O2 waveforms [with 0.5 volts as centerline] and the number of cycles [lean -rich-lean] per minute.

The ecu understands anything over 0.55 as rich and anything under 0.45 as lean.

http://autolabscopediagnostics.com/sensors2.html
Look at before [old O2] and after new O2 waveforms.

Did the readings that I gave I think 3 posts back help any? As I mentioned, neither one of them would alternate, they both maintained a certain voltage at a given rpm. Does it sound like I have bad o2 sensors or does it sound like something deeper?

[Infinitiguy19]

With you laptop consult you can still perform the same test a Nissan Consult thanks to Q45Techs info.

Maintain 2000 RPM's and see if the O2 sensor voltage goes from over 0.55 volts (rich) and under 0.45 volts as (lean). Do that for 10 seconds and make sure it goes from rich to lean, rich to lean... 5 times. If not then replace the O2 sensor(s) at fault. Assuming the above is correct.

[mattd1979]

The results that I posted originally show that neither sensor would alternate from high to low. So I guess both sensors are bad. I managed to only get the driver side sensor replaced. The o2 sensor socket rounded the corners on the passenger side sensor. I am going to have to figure out what size the reducer fitting is that the sensor is screwed into and try to get it out. Then I can put the reducer fitting in a vice and use a box end wrench to remove the sensor from the reducer fitting. Anybody have any ideas as to what size the reducer fitting is?

Since I posted the above I went outside and have hooked up the laptop to the car. With the engine at 2000 rpms using OBD Scantech, I am getting a reading of 0.930v on the left sensor which is new and I am getting a reading of 0.320 volts on the right sensor. Neither are fluctuating up and down as you described. When I switch it to the guages, the needles are pratically steady on the voltages that I just mentioned.

[Q45tech]

You must heat up O2 for ~ 5-10 minutes to simulate a steady highway speed [2000 = 60 mph].
The heaters get weak and the sensor gets sluggish, eventually [30 minutes] almost every O2 will switch.

What new O2 do is greatly speed up the time to first switch so the mpg economy gets better faster.

The ecu is baised to hold a dead sensor at 0.4-0.6 so ecu is preprogrammed to produce 14-16 A/F regardless [without switching].

To get the finest best emission HC and CO the system must be zeroed in on 14.7 A/F because the cats are metallurically optimized for that.

Now E10 changes all that the 3.3% extra O2 in fuel FOOLS O2 sensor and ecu to enrichen the injection pulse by 3.3% MINIMUM so engine uses more fuel.........but that factor alone is only ~~~ 0.5 MPG.

Hopefully everyone learns how the adaptive learn works to zero in on the minimum injector pulse at a steady rpm/speed that will achieve the highest probability of ~~14.7 A/F.

But the O2 sees 4 cylinders so it is an average of all 4 since the fuel trim is a bank of 4.

For self protection the system cannot lean things to much [melt pistons/valves from extra heat] so +- 20% is rarely achieved even with a single dead coil or injector.............2 coils or 2 injectors in the same bank can be a real problem if one keeps driving.

[mattd1979]

You must heat up O2 for ~ 5-10 minutes to simulate a steady highway speed [2000 = 60 mph].
The heaters get weak and the sensor gets sluggish, eventually [30 minutes] almost every O2 will switch.

What new O2 do is greatly speed up the time to first switch so the mpg economy gets better faster.

The ecu is baised to hold a dead sensor at 0.4-0.6 so ecu is preprogrammed to produce 14-16 A/F regardless [without switching].

To get the finest best emission HC and CO the system must be zeroed in on 14.7 A/F because the cats are metallurically optimized for that.

Now E10 changes all that the 3.3% extra O2 in fuel FOOLS O2 sensor and ecu to enrichen the injection pulse by 3.3% MINIMUM so engine uses more fuel.........but that factor alone is only ~~~ 0.5 MPG.

Hopefully everyone learns how the adaptive learn works to zero in on the minimum injector pulse at a steady rpm/speed that will achieve the highest probability of ~~14.7 A/F.

But the O2 sees 4 cylinders so it is an average of all 4 since the fuel trim is a bank of 4.

For self protection the system cannot lean things to much [melt pistons/valves from extra heat] so +- 20% is rarely achieved even with a single dead coil or injector.............2 coils or 2 injectors in the same bank can be a real problem if one keeps driving.

The engine temperature was at around 193 degrees when the most recent readings were taken with the new sensor installed on the driver side and the old sensor still in on the passenger side. The readings from both sensors were steady at 2000rpm. The only difference now is that the left sensor which is the new one is giving me a reading of 0.930v. Slightly higher then the old sensor and the right sensor is giving me a reading of 0.320v. Other then that, they both stay steady at 2000rpm. Now they do change slightly as I increase or decrease rpm. When I stomp on the throttle, they both jump up to around the same .930 and drop off to .001 or .000 when I let off the throttle but when maintaining any certain speed, neither fluctuate between low and high. For example, If I followed what Paul Wall said, then the left sensor would stay reading .930v and the right sensor would continue to read .320v for the entire 10 seconds at 2000rpm. There must be a problem deeper then the o2 sensors if the new sensor is apparently reacting the same way as the original sensor was on the driver side.

[mattd1979]

Does anybody know what size the reducer fitting is that the o2 sensor screws in? I'm going to try to get a socket of the right size to remove the reducer in order to get the sensor out. And Paul Wall, when you had your consult adapter and laptop connected to the car, did you see how the gauges displayed the readings of the o2 sensors? Did the needles jump from high to low voltage and back as you described to me at 2000 rpm? If so then there must be something other then the sensors bad on my car because as I mentioned earlier, the new sensor is reading steady just as the older one was doing.

[Infinitiguy19]

I never performed the test but I might do it tomorrow. I will let you ASAP what I get out of the test. But Q45tech hasn't said I was wrong so I assume I am correct in assuming the test is correct.

Sorry not sure on the O2 sensor fitting.

[Q45tech]

Try swaping in your spare ecu to see if any changes in O2 [the one that appears stuck].

[mattd1979]

Try swaping in your spare ecu to see if any changes in O2 [the one that appears stuck].

The needles don't stick, they just don't jump from high to low voltage like for example 5 times high and low within 10 seconds. The readings will gradually climb with the rpm. The left sensor reads higher then the right. But other than that, neither of them fluctuate high and low. When I let off the throttle rapidly after holding it at 3000rpm, the sensor readings will drop to .001v for the left and .000v for the right and climb back up to .930v for the left sensor and .750-.830v for the right sensor. And when I stomp on the throttle, the left sensor reading will fall to .200 and then climb to.930v. The right sensor will drop to.001 for a second and then climb to .780v Once I reach 3000rpm. As soon as the rpm levels off at any given rpm, the left sensor will read around .900-.980v and the right sensor will read around .300-.340v.

I will try swapping ECUs to see if it makes a difference. I may not be able to though until the following weekend as I have been working two jobs.

[djwarner]

Your readings are telling the ECU that one bank of cylinders is rich and the other bank is lean.

So what's a fella to do? Adjust the mixture leaner, richer or keep it where it is? Apparently, keep it where it is.

As I understand it, you changed one sensor and not the other. After changing, the consult readings changed but are still not normal. If this is correct, changing the other sensor would be the next logical step.

[mattd1979]

I've got to figure out the correct size I need to remove the reducer fitting on the passenger side. As for a difference in reading, there really isn't that much of a difference between the new sensor and the original when you compare the two. The new sensor is reading high just as the original was. I have a feeling that the replacement sensor for the passenger side will not be reading much different from the original either. I was told that the sensors should both be switching from high to low so many times every ten seconds. Paul Wall is going to look and see what kind of readings he is getting and see whether or not his sensors switch high and low or stay steady like mine. That way we can compare the two.

[Infinitiguy19]

Hey Matt I am a little busy but I have to fix something on the Q tomorrow (Everyday is Q day it seems). But I will do my best to get some O2 sensor readings, Keep in mind my O2 sensors are not new and need replacing also.

In the mean time here are some things you might find helpful:
http://spreadsheets.google.com/ccc?key= ... UN0E&hl=en
http://spreadsheets.google.com/ccc?key= ... zTmc&hl=en

http://picasaweb.google.com/lh/photo/MR ... directlink

http://picasaweb.google.com/lh/photo/M4 ... directlink

[url]http://picasaweb.google.com/lh/photo/2d ... directlink[/url

Blue and Yellow are O2 sensors

Orange and Green are Fuel Injectors

Y axis is RPM

X axis is time

[mattd1979]

I reset the ECU self-learn while the engine was running but nothing changed.

Paul Wall, have you had a chance yet to see what kind of readings you get from the sensors?

[qship96]

forget the readings on the old ones and just install 2 new ones and forget about it for a decade or so.

[Q45tech]

Absolutely, one of the problems on NICO is members income varies and how much they value their spare time.

After taxes my spare time is worth about $31 per hour plus 50% on weekends or after 5pm.
Why I think paying Byron $40 per hour is a deal even though I'm there watching.

"Yeh the AMG C43 is ready from the [MB specality] shop after a month and ordering special Baum tools* to fix a massive front cover leak. This C43 is 3x worse [expensive and painful] than any [90-06] Q45 ever built. Everything [parts] is 30-45% more expensive'

These tools are necesssary to remove the crammed in viscous fan drive to remove belts to get to front cover leak to replace observation port that now has an upgraded part.
The horror dozen of quarts of Mobil 0w40 on the ground and in various parking lots just like BP.

[mattd1979]

Can anybody that has a consult clone, like obdscantech or ecutalk, connect to it when you have the time and see how the readout is on the sensors. Are they switching ON and OFF or High and Low volts or are they maintaining a certain voltage at a given rpm? I have a new sensor installed on the driver side as I said earlier in this thread. It is doing the same as the old one. I am going to replace the other but I have to first get the old one out which requires a socket that is big enough to fit the reducer fitting so that I can remove the fitting in order to remove the sensor. I mentioned all of this already earlier in the thread. I feel like some people just don't read all of the prior posts before they answer, or they just forget it. I just want to see if other people get readings similar to mine. I get the feeling that when I replace the other sensor, the results will be the same as with the driver side sensor. My mom has a '91 Q that I could use to compare but It won't be available for a while. If this is a problem beyond the sensors, I want to take care of it.

Matt

[Lokim]

It sounds to me as though your MAF is reading wrong or you have a vacuum leak causing the motor to dump fuel. Maybe even leaking injectors. How does the car run overall? How is your fuel mileage? Maybe try a bottle of Techron through a tank...

[goody90q45]

Can anybody that has a consult clone, like obdscantech or ecutalk, connect to it when you have the time and see how the readout is on the sensors. Are they switching ON and OFF or High and Low volts or are they maintaining a certain voltage at a given rpm? I have a new sensor installed on the driver side as I said earlier in this thread..........

Hey Matt- I hadn't used my Nissan Data Scan for a while so I plugged it in and made a few runs this morning. The scale is 0-100. Both sensors reacted the same. I'm not sure if it's voltage or % but here goes:

>> Idle at 700rpm.....3-6 with little movement
>> Hard acceleration up to 3000rpm.....5-95 flopping 2-3 times a second
>> Hard acceleration 3000rpm to 5000rpm.....Steady at about 90-95
>> Steady cruise, 40mph, 1700rpm.....15-85 flopping about 2 times a second
>> Decelleration from 45mph to 20mph.....Pegged at 90-95

You can break out the oscilloscope and probably get a lot more detail but I think the readings under hard acceleration (2-3 times a second, 5%-95%) are the most inmportant in telling you whether the sensors are working properly. I hope this helps.