Bad o2 Sensor?

[tattooed_pariah]

Do o2 sensors go bad? or are they one of those "it works or it doesn't" items?

Mine says "AIR" probably 96% of the time, "LEAN" for about 2%, and actually gives a reading the other 2%..

Since it kept saying AIR and LEAN, I jetted my carbs (dual 40IDFs) SUPER rich... like 70 idles, 115 mains, and 200 ACs.. it feels good, running strong, has power all across the RPM range, doesn't backfire or sputter and fires right up. but I'm wondering why I almost never can get a AFR reading.. When I do, it seems to be about 3k rpms and around 70% throttle, and then it's between 11 and 15, mostly 12-13, but as low as 11 and high as 15..

Cylinder temps stay under 280, and oil temp stays under 180.. I would think if it was actually super lean, i'd be running excessively hot as well, and super rich would drop temps right?

I don't think specs really apply to my original question, but for those that will reply just to ask what they are, here you go:

1776cc
AS41 case, bored, clearanced, drilled and tapped for full flow
doghouse cooler deleted, -8 lines to external oil filter, to 72 pass cooler with 10" fan on a 180F thermostat switch
36hp fan shroud
69mm DPR CW crank
stock rebuilt rods
Engle 110 Cam and lifters
Brothers 40x35.5 heads
dual valve springs, chromoly retainers
bolt together 1:1 rockers with swivel ball adjusters
dual Spanish Weber 40IDFs (jetted as above)
Compufire Dual cool 90amp alternator
MSD 6al Ignition Box
MSD Billet Distributor
MSD High Vibration Blaster 2 coil
MSD plug wires
freeway flyer transaxle

I think that's about it...
_________________
-pariah (just a novice from "that other VW site")
'72 Volksrod "Effigy"

"Never worry about stepping on people's toes. People who get their toes stepped on are either sitting down, or standing still on the job."
-Admiral Arleigh Burke, USN(ret.)

[ps2375]

Is it a WideBand or a NarrowBand sensor/controller? Sensors can go bad and if you leave the sensor in with no power to it, it can shorten sensor life.

[tattooed_pariah]

[FreeBug]

How airtight is the exhaust? Any misfires?

[ps2375]

Well, if you can free air calibrate it, I would do that first. Then maybe look for another sensor. Not sure how easy or expensive the 4.2 sensors are.

[tattooed_pariah]

[mikedjames]

I have the PLX setup and if I jet the engine really rich or the choke is stuck on, eventually the AFR gauge stays at 20:1 all the time and occasionally drops to 12:1.

Get the jettiing back in the ballpark and the lambda sensor burns off the soot and starts working again.

As it gets older it gets more temperamental , at 50 k plus miles it really needs a new sensor.
_________________
Ancient vehicles and vessels

1974 VW T2 : Devon Eurovette camper with 1641 DP T1 engine, Progressive carb, full flow oil cooler, EDIS crank timed ignition.
Engine 1: 40k miles (rocker shaft clip fell off), Engine 2: 30k miles (rebuild, dropped valve). Engine 3: a JK Preservation Parts "new" engine, aluminium case: 26k miles: new top end.
Gearbox rebuild 2021 by Bears.

1979 Westerly GK24 24 foot racer/cruiser yacht Forethought of Gosport.
1973 wooden Pacer sailing dinghy

[Bugsy61]

Don't forget that you can go so rich to cause a misfire, the reading will jump to full lean, because a misfire does not use up any of the oxygen. In the end, your measuring oxygen content in the exhaust, not how much fuel your burning.

[Coyotemutt]

I have the same system. I don't get alot of miles out of the sensors for some reason. I run lean through most of my cruising and it only tips rich for full throttle operation, so I know it isn't getting full of soot.

When mine fails it tends to read LEAN 100% of the time. When it is working properly it will read AIR when the sensor is warmed up and the engine isn't running.

If I go way too rich it reads LEAN until it can get a reading within the range it can handle. What's weird is that it will peg 10:1 when the sensor is brand new and then slowly starts to fail to read excessively rich readings over time.

What do your plugs look like, btw? I like to check my plugs against the wideband readings to make sure it isn't lying to me.

[gprudenciop]

I have had 2 o2 sensors go bad and they slowly failed. Going lean little by little.do you know what sensor you are running? The ones that went bad were bosch lsu 14.2..
_________________
Never look down at anybody unless you are helping them up..
Loaning someone your strength instead of reminding them of their weakness = kindness..

[VW_Jimbo]

O2 sensors go bad. Get a DVOM connected in between the harness connector and read the millivolts. Should show voltage from .1 to .9, back and forth based off of oxygen left from the burning cycles of each cylinder.

This is from http://www.autodiagnosticsandpublishing.com/feature/o2-sensor-testing.html

"A big misconception among technicians trying to understand O2 sensors is that they cycle by themselves. The O2 sensor just reads oxygen content in the exhaust, THAT’S IT. Excess oxygen in the form of regular ambient air will send the O2 sensor voltage signal low (under 0.450 volts) and lack of it will send the voltage signal high (over 0.450 volts)."


Additionally, they need to get hot and remain hot. If they are not reaching their designed operating temperature (above 600 degrees F) or better, their life declines rapidly. You may need to locate to a hotter spot.



Also, you may be able to install a heated O2 sensor for better readings, if it is located in a cold spot.

From http://autoditex.com/page/lambda-sensor-o2-sensor-21-1.html

" Single-wire lambda sensor was used in the early injection systems with a feedback (lambda regulation). It has only one terminal, which is the signal terminal. Sensor ground is its housing and it connects to the engine ground through the exhaust pipes.
Two-wire lambda sensor has a separate grounding cable. It was used in the early injection systems with a feedback (lambda regulation) also.
Disadvantage of the single-wire and the two-wire sensors is that their operating temperature range starts at 300 ºC. Sensor will not work and will not produce a signal until this temperature is reached. It was necessary for the sensor to be mounted as close to the engine cylinders as possible in order to heat and wrap from the hottest exhaust gases stream. Process of heating the sensor slows down the regulation process of the onboard controller because of the feedback. In addition, using the exhaust pipe as a signal ground requires sensor’s thread to be coated with a special electrically conductive paste, which increases the possibility of a bad contact in the feedback circuit.
In the three-wire lambda sensors, is a special heating element inside which is constantly turned on when the engine is working and thus it’s reducing the heating time of the sensor to the working temperature. This allows installation of the sensor on the exhaust manifold, near the catalytic converter. Disadvantage is the need of electrically conductive grease.
In the four-wire oxygen sensors - two of the terminals are the heater terminals and the other two, the signal terminals."


Those four wire O2 sensors are awesome but expensive!
_________________
Jimbo

There is never enough time to do it right the first time, but all the time necessary the second time!

[mikedjames]

Despite having my sensor go to the 20:1 end of things a while back with choke 12 volt DC wire dropped off the progressive carb.

For instance today I drove the bus 150 miles along roads at between 40 and 70mph and the AFR showed exactly what I expected : WOT at 70mph and 12.5:1 AFR or 40mph in 3rd up a fairly steep hill.. Fast cruise 60-65 around 16:1, Foot off gas and engine braking 20:1 (and popping..)

So I maintain, soot can be burnt off provided your mixture is lean enough to not produce soot all the time.

If you richen up in this state it just gets worse...


Another fun thing about the PLX system is that a single cylinder misfiring at idle shows up as a very rapidly changing AFR which is leaner than it should be as the unreacted oxygen appears as pulses in the exhaust.

The older PLX setup I have uses a Bosch LSU4.2. Bought in 2011. Its been on the bus for 50+k miles
_________________
Ancient vehicles and vessels

1974 VW T2 : Devon Eurovette camper with 1641 DP T1 engine, Progressive carb, full flow oil cooler, EDIS crank timed ignition.
Engine 1: 40k miles (rocker shaft clip fell off), Engine 2: 30k miles (rebuild, dropped valve). Engine 3: a JK Preservation Parts "new" engine, aluminium case: 26k miles: new top end.
Gearbox rebuild 2021 by Bears.

1979 Westerly GK24 24 foot racer/cruiser yacht Forethought of Gosport.
1973 wooden Pacer sailing dinghy

[clonebug]

[FullFender]

I had 3 Innovate/Autometer sensors go bad within 2-3 weeks of getting them, all different error codes.

Bought a PLX MultiGauge and all my problems went away...

[Coyotemutt]

My plx run A on an LSU 4.9 sensor. The sensors barely make it a year before they start having faults. I may have installed it wrong though, as I have it exposed to direct exhaust flow right after the collector.

Maybe the 4.9 doesn't last as long.

[clonebug]

[Coyotemutt]

[tattooed_pariah]

I think my bung is installed facing directly towards the front of the car :/ sounds like it should have been placed higher on the pipe a few degrees..

got a bigger potentially problem now though, went to start this morning, turn the key and hear and feel a loud *CLUNK*

stopped turning the key, sat for a second, then tried again and heard no movement.. We've had REALLY bad rain over the weekend, so I suspect that rain came in my decklid, probably soaked my air filters, condensed inside the air filter housings, and dropped into the intakes :/

I know in Virginia it was always hard to start after rain, but it was never outside in storms like this.. gonna have to wait for the rain to clear, pull the plugs and see if it cranks/spits water out.. if it doesn't, then I got bigger problems
_________________
-pariah (just a novice from "that other VW site")
'72 Volksrod "Effigy"

"Never worry about stepping on people's toes. People who get their toes stepped on are either sitting down, or standing still on the job."
-Admiral Arleigh Burke, USN(ret.)

[mark tucker]

a short ex system or o2 sensor too close to the outlet(end of exhaust pipe thingy)can bring in cooler air and throw off the o2 thingy, a heated o2 thingy helps a lot. also octane boosters and other fuell treetments can/will throw off the readings and can take a while to burn off the O2 thingy after fresh fuel with no additive is run through.

[tattooed_pariah]