Oxygen Sensor

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Date: Thu, 20 Feb 1997 16:31:44 -0800
From: Scott Wilson 
Subject: V6 O2 sensor
To: Toy 4x4 List 

I'm writing this for all you V6 guys out there.  Hopefully this will
save you the month I spent trying to find the correct O2 sensor for my
truck.

STEP 1:	 GET YOUR MEMBERSHIP TO TLCA	
STEP 2:  GO TO YOUR NEAREST TOYOTA DEALER AND BUY THE CORRECT O2 SENSOR
STEP 3:  INSTALL IT.

This story starts out when my engine light started coming on and giving
me two error codes 25) air/fuel mix rich, and 26) air fuel mix lean.  I
began going down the list of possible fixes in my Hanes manual starting
w/the cheepest.  I was soon down to the O2 sensor and the PCV valve
(which is a pain in the rear to replace on a V6)  I heard from guys on
this list that Bosch made a good O2 replacement, So I went off to get
one.

I talked to the guys at Kragens an they ordered me one. (I also got a
PCV valve at the same time)   Their computer had none listed for the V6,
so without telling me they special ordered my one for the 4 cyl (Bosch
$35).  It arrived a week later, and it didn't work. (didn't even fit!) 
I brought it back and they ordered me another brand (Carter $55).  It
arrived a week later.  Turned out to be a Bosch sensor in a Carter box!
By this time I had just replaced the PCV valve and the engine light
stopped.  I returned the O2 sensor, ate the 10% restocking fee, and went
on my marry way.

Five days later the light was back on, same error codes.  I reordered
the Carter O2 sensor, it came in a few days later, and I tried to put it
in that same night.  Didn't fit!  In fact after I found it didn't fit I
checked the part # and sure enough, it was the same as the 4 cyl Bosch
sensor.  It was just in a Carter box, and the price was $20 higher! 
While I was under the truck this time I cut the weather proof sleeve
around the wires going into the original sensor.  It had 4 wires.  

Today I called Stevens Creek Toyota and they had the correct O2 sensor
in stock for my truck for $140.  I heard from a guy on this list
yesterday that this dealership gives 25% off parts to TLCA members.  I
showed up to get the sensor and showed them my TLCA membership card and
they took 32% off the price!!  He only charged my $95 for the O2 sensor.

(Attention non-TLCA members  Join TODAY!  My $20 membership saved me $45
just today!!!)  

Then I returned Carter sensor to Kragens (without any restocking fee)
and showed them the one I just bought from Toyota.  They said they don't
have a replacement like the one I showed them, so they couldn't have
helped me anyway.

PLUS!  Unlike the Bosch replacement, where you have to cut and spice the
wires, the Toy O2 sensor is a complete replacement.  The entire sensor
assembly, wires sealed in weather proofing, and the 4 wire connector is
included and is one piece.  It even included a new boot for where the
wires enter the cab of the 4Runner!  So when I install it tonight, it'll
be as easy as taking the two nuts holding the old O2 sensor off,
unclipping to old one, clipping in the new one, and putting the two nut
on to hold the new one!  Piece of cake, no cutting, no spicing!

I let you know if this finally stops the engine light from appearing.

Hoping this save someone a lot of time and frustration,

Scott

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Date: Thu, 10 Apr 1997 13:23:37 -0400
From: Jughead 
Subject: O2 SENSOR
To: toy4x4@tlca.org

I have a Downey header with 2.5" tubing and a flowmaster (no cat.
conv.) on my 22RE. When I installed the exhaust system I mounted the
oxygen sensor in the same location it was in the factory system (approx.
a foot behind the trans. cross-member).

 I am about to redo the whole system in stainless steel. What I was
wanting to know was if it's best to put the oxygen sensor where I have
it now, or if it would be ok to move it closer to the engine (possibly
on the collector of the header)?
 
- ---------------------------------------------------------------------
           James Owens
        (Jughead@141.com)            '92 Std. Cab 4x4 w/22RE
            Machinist            5.71 w/ Det. Locker & True-trac
          Williston,Fla.            36x12.5x15 Super Swampers

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Date: Thu, 10 Apr 1997 14:52:46 -0500
From: Jack Alford 
Subject: O2 SENSOR
To: toy4x4@tlca.org

>wanting to know was if it's best to put the oxygen sensor where I have
>it now, or if it would be ok to move it closer to the engine (possibly
>on the collector of the header)?

The most important thing about placing an 02 sensor is to try and keep it
the same distance from the engine as the original was. 02 sensors work alot
off of heat so the distance from the engine is critical for the computer
to run the engine correctly, I'd put the 02 sensor back where it was on the
stock exhaust.


 
 -----------------------------------------------------------------
 Jack Alford              Off-Road.com - The best dirt on the net!
 jalford@off-road.com              http://www.off-road.com/
 Decatur, AL

             '86 Xcab Toyota Pickup -  33x12.50 BFG MT
         Solid Front Axle - Marlin Crawler - ARB's - 4.88's
         SFWDA  -  TLCA #3415  -  Rocket City Rock Crawlers

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Date: Fri, 11 Apr 1997 10:45:33 -0600
From: Tony Bartlett 
Subject: Oxygen Sensor placement
To: toy4x4@tlca.org

I think you want if fairly close to the manifold, to work properly they
need to be hot,  nowdays they have built in heaters so they can put them
before and after the cat. to keep an eye on efficiency.  you could buy
one with a heater if you need to put it downstream a little.

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Date: Fri, 08 Aug 1997 18:11:51 -0700
From: James Brink 
Subject: O2 sensor
To: Toy4x4@tlca.org

Michael Henry wrote:
> 
> Speaking of O2 sensors, how would they affect the mixture on my carburated
> 22R?  It makes sense on the Fuel Injected trucks, but I don't see what the
> sensor is going to be able to change on a mechanical system.  As a little
> aside, anybody else out there running the Downey DGAV Weber downdraft kit?
> Supposed to be a stock replacement, but mine has never really worked right
> from very early on.  I'm going to have it gone through by a specialist,
> but I would like to know if there are any common problems to look for on
> this setup.  It is the one that Downey refers to as the "street lethal"
> carb.

The carbureted Toyotas use a "feedback" air/fuel system. The oxygen
sensor monitors the air/fuel ratio and adjusts the air suction system to
correct for proper mixture by injecting metered amounts of air into the
exhaust sytem, similar to an air injection system.

- --
Jim Brink				1986 Standard Bed 4X4/22R/M5
Toyota/ASE Certified Technician		32"BFG All-Terrains
(brinkjm@earthlink.net)			LockRight/4.10 Gears
***********************************************************************
TLCA# 6184 / Friends of the Mojave Road (FOMR) / MRVMA-DESERT EXPLORERS

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Date: Tue, 30 Sep 1997 13:04:44 -0700
From: James Brink 
Subject: oxygen sensor
To: Toy4x4@tlca.org

Agustinus Gunawan wrote:
> 
> This is the second time I post this.
> Does any body know when to change the oxygen sensor:
> * Every 60000 miles?
> * When the check engine light comes on?
> * When the mileage drop considerably?
> * Etc?

The recommended replacement interval is 60,000 miles, to comply with
Federal and California emissions warranty compliance. It is a safe way
the manufacturer can assure the vehicle will comply with certified
emissions standards after "deterioration" over so many miles have
accumulated on the vehicle fleet. Replacement is not really needed
unless the sensor is bad.

If you have a check engine light illuminated and the codes reveal an O2
sensor problem, do not assume the sensor is the cause...Investigate a
little further...

The oxygen sensor surely could be the cause of your mileage problems;
but I would not condem it immediately. The operation of the oxygen
sensor depends heavily on other engine and EFI components. 

Most of the O2 sensor failures I have seen have been due to
contamination (from an over-rich mixture caused by faulty fuel-delivery
systems) or internal breakage of the electrical components. I have never
seen one that has just gone haywire for no reason.

Yes, you can check the O2 sensor with a voltmeter through the EFI/TCCS
diagnostic connector. The best check is for "crosscounts" or how many
times the O2 sensor fluctuates between rich and lean. The cycling should
be frequent and consistent. If the crosscounts are low, suspect a "lazy"
sensor due to contamination or faulty wiring. The frequent cycling
indicates the EFI system is in closed loop, or the system is operating
to maintain optimum fuel/air ratio, 14.7:1, (one pound of fuel for every
14.7 pounds of air entering the intake system) or "Stoichiometry."
> 
> How to make sure my oxygen sensor is defective?
> * Voltage Drop?
> * Resistance? I think Jason told me about ~0.9 ??at  Wide open trottle.
> * Any other symptom? (rough idle or rough on high RPM?)
> 
> My truck has 125K miles lately I have been getting 15-17 MPG.
> I want to make sure it is the faulty oxygen sensor or not. The Dealer quote
> me $135.62 for original Toyota Turbo oxygen sensor.  

Sounds about right.

Of course, the OEM Toyota sensors are the best ;-) ! 

I would begin with a basic diagnostic inspection of the intake, fuel,
ignition, and exhaust systems. Next, check all of the sensors
systematically with a factory repair manual. Do you have access to a
four-gas exhaust analyzer? Measurement of HC, CO, CO2, and O2 is a good
approach to take to determine where to start. HC is related to the
ignition system, CO is the fuel/intake system. O2 tells how much oxygen
is present in the exhaust system (exhaust leaks can really fool an O2
sensor when they occur upstream of the sensor). CO2 shows how well the
mixture is being utilized for combustion and ultimately how your fuel
economy will be reflected.

Maybe Ed Wong could elaborate on how the electrical stuff works...? (My
weak point..)

Perform a thourough diagnostic, with the 4-gas if possible, and report
back what you have found. No need to waste $135 on a new O2 sensor if
the problem is a bad $50 fuel injector...

- --
Jim Brink--Toyota/ASE Certified Technician             '86 Std. Bed 22R
Manhattan Beach, CA				   32x11.50/15 BFG M/Ts
(brinkjm@earthlink.net)                            	
************************************************************************
TLCA# 6184/ South Bay Roughwheelers / Friends of the Mojave Road (FOMR)

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Date: Tue, 30 Sep 1997 20:31:23 -0400 (EDT)
From: DRM033@aol.com
Subject: Oxygen Sensor
To: Toy4x4@tlca.org

In a message dated 97-09-30 17:52:53 EDT, you write:

> 
>  I've got a '90 V6 4Runner and my manual says to have it changed
>  at 80k miles. The manual also says that it's a "free" service!
>  Here's the deal, I've got 95k miles and haven't changed it yet.
>  Are the dealers still obligated to change it? I think mine's
>  busted cuz my mileage is horrible. Of course, that could be a
>  million things.
>  
>  -Richard

Having personally gone through 3 Oxygen sensors (and a computer, but that is
another story) I feel like I have a good grasp on what it is like when one
goes (and the cost - $135 ea.).  It runs fine 90% of the time.  Mine would
run OK but not great most of the time, but it would miss while driving.
 Usually at high RPM, but sometimes at idle.  The main thing I noticed was
that it was an intermittent problem.  I noticed no real decrease in fuel
mileage, but then I was not really paying attention.

On another note, people keep asking if their timing chain is going or not. On
my 22RE, it was OBVIOUS.  I had broken a tentioner, and the slapping sound
was very prominent when at highway speed and letting off the throttle.  It
would go away with acceleration.  

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Date: Tue, 10 Jun 97 08:38:00 -0500
From: "George Szappanos"
Subject: Engine Performance:
To: 

     Not to be petty, but I don't like to see less than totally accurate 
     information get proliferated.
     
     EWong wrote:
     
     >"It turns out that the "best" power is obtained just "before" 
     detonation starts occuring in an engine - aka - just on the lean side 
     *before* the onset of detonation."
     
     First of all, best power for a large majority of engines (daily 
     drivers and big buck racers) is at around 12.5:1 air-to-fuel ratio.  
     That's about 18% RICHER than stoichiometry. This is true for 
     wide-open-throttle only (WOT)- all modern engines run at stoich or 
     leaner putting around town.  Best power is generated at this ratio due 
     to combustion chemistry, but it also helps to cool the combustion 
     temps as compared to stoich. At this ratio, NOx is down but HC & CO 
     are way up, fortunately the EPA has no specification on WOT emissions. 
     
     Secondly, fuel mixture has little to do with detonation (at least 
     directly).  Detonation, or spark knock, is caused by the spontaneous 
     and rapid ignition of the fuel mixture due to elevated temperatures 
     and pressures present in the combustion chamber.  Ignition timing is 
     the primary variable governing knock.  Richening the fuel mixture does 
     help to slightly cool the mixture, but at 12.5:1 AFR, combustion is 
     optimized which has the effect of maximizing temperature. 
     
     EWong wrote: 
     > "If you put an air/fuel meter on the exhaust on a stock EFI engine - 
     you will see the ratio (actually the on/off - stock O2 sensor are 
     really not that accurate) scroll back and forth from *rich* to *lean*. 
     This is done for EPA reasons."
     
     The stock O2 sensors are actually extremely accurate.  The reason they 
     "scroll" or switch is because this type of narrow band sensor can only 
     distinguish rich or lean mixtures.  When the sensor says it lean, the 
     PCM adds more fuel and vice-versa.  Most good system switch faster 
     than once a second and allow no more than a .2 ratio swing. Modern 
     catalysts need to run right at stoich for proper oxidation and 
     reduction of exhaust emissions so it's imperative that ratio is 
     maintained.
     
     
     Geo.

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