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2003 O2 sensor question

3K views 15 replies 6 participants last post by  Redtruck-VA 
#1 ·
Trusty old Redtruck is back running on the OEM PCM. Watching my AeroForce Interceptor AFR I'm seeing some pretty erratic swings. Keep in mind this is not reading the OEM O2s but an installed wideband. So I started watching the OEM Front O2s voltage and I'm getting some pretty wild swings there also with readings jumping from 40 micro volts (mv) to 850 mv. I thought I had two spare O2s but when I went to actually plug one into the wiring harness the plug is keyed ever so slightly different. I believe the two sensors I have are for 04+ model using two front O2s. Anyone needing these can contact me. Now my question, what is the normal O2s voltage reading while just driving around? The PN for a 2003 O2s is 56041698AA I'll be replacing my old one soon. Any input is appreciated.
Thanks,
 
#3 ·
The 03 model uses only one forward sensor and it's factory location is where the two header pipes join together. The 04+ models use two forward sensors and they are located in each header pipe forward of the individual cats. The abbreviation "O2s" stands for "O2sensor". On my truck I use a single sensor located on the passenger side header collector. Looking at sellers on the internet I see universal O2s being sold with a widen slot for different plug keys to fit. I may try trimming the key slot on one of my spares to see if it'll work.
Here is an example of the wide key slots to fir various plugs.
More Information for STANDARD MOTOR PRODUCTS SG1849
 
#4 ·
I would think the O2 voltage would or should be the same all the time. I've never heard of anyone monitoring voltage on O2's before. All I know is that you can get some funny o2 readings if you have them mounted near a place that could potentially have turbulence such as near a CAT or near the tailpipe. I have them on my dragster about 6 inchs from the ends and they were getting backdraft and reading lean because of the fresh air coming up the pipe so i had to mount them further up. I'll see what i can find out about o2 voltage though..
 
#5 ·
I'm sorry, this can be difficult to explain. My question was directed at what a normal reading/fluctuation might be.
The narrow band O2s signal voltage is the input to the stock PCM to adjust AFR and is in the less than 1vdc measured in the micro volt range. You, I suspect are using a wideband for mainly datalogging purposes.
I believe the OEM O2s narrowband signal output should be more stable than what mine is reading. I'm not getting any DTC's except for an occasional "Rich" condition.
With the MAP/TPS signals in conjunction with a O2s signal change should determine if the signal change makes for a richer or leaner fuel condition as the narrowband sensors only reads accurately in a very narrow band. It can be difficult for the PCM to compute which condition to go to without a TPS/MAP input indicating whether the engine is under load or decelerating. I'm seeing an occasional rich condition while decelerating and think my O2s is not reading as it should and sending false signals to the PCM. So back to my question, for those who have the gauges that can read their O2s voltage outputs, are you seeing a steading reading or does it fluctuate somewhat erratically?
 
#6 ·
The '03 trucks use an O2 sensor that is a different style than '04 and up. (chemically) They are a battery and will basically toggle the output voltage that you are seeing when they sense an AFR above or below 14.7. The PCM 'pings' the O2 sensor by momentarily increasing then decreasing the fuel delivered and watches for the O2 signal to react appropriately. When they stop detecting the ping, a code is set for a bad sensor, or bad catalytic converter if the ping makes it to the rear sensor without the fuel spike being absorbed by the cat.
 
#7 ·
Short answer: A new healthy sensor will switch between approx .2Vdc and .8Vdc several times per second and slow down with age until they stop switching. Normally this causes the engine to run rich and fuel economy goes to sh*t.
 
#8 ·
NGK Website:

'03: Zirconia oxygen sensors produce a voltage which varies based on the amount of oxygen in the exhaust gas.

'04+: Titania oxygen sensors vary in resistance based on the amount of oxygen in the exhaust gas.

Any splices in the signal wire will weaken the signal and offset the signal to read slightly rich. I cut out 2 soldered joints and replaced with 1 high quality water proof crimp connector and this alone moved my wide band reading from 14.4 average to 14.6 average. My truck had improved fuel economy by simply using a better splice.
 
#12 ·
Any splices in the signal wire will weaken the signal and offset the signal to read slightly rich.
Hmmm. Greg what does your harness look like after all the recent work? Any splices on these wires?
 
#13 ·
The comp constantly adjusts the fuel trims while at same time holding 14.7 it adds fuel sees over takes fuel very fast this is how it holds the 14.7 afr which also leads to fuel trims short and long short term should always be near zero or no more than +/- 5 long term trims are what really tells you how the eng is running anything over at 15% or -15% means you had a lean or rich condition and usually leads to an eng light

Keep in mind the comp cycles the o2s anywhere between 50-200 times a sec so its ery fast the scanners on catch a glimpse of what's really going on there refresh rate is about a 5th the PCM speed as long at long and short are near zero- +/-10 your good eng is running nicely
 
#14 ·
This is great info and as usual Frostking is the goto guy. I appreciate all the inputs. The O2s wiring is unmolested. But I did have a couple sessions that the engine was running lean and hot enough it burned out the Magnaflow muffler. It took much longer to gain control of the AFR then I would recommend to anyone. I think the OEM O2s may have been damaged during these sessions. The cats are probably also shot. The O2s voltage is really jumping around, so I think I'll change the front O2s to see how it works with a new one installed. I also have a 05 fuel pump set to 58psi instead of 48psi so the PCM has to pull fuel just to run within the normal range. I installed a Split Second "Cam Tuner" which should lean the AFR when adjusted and it did the opposite in as richens the mixture with any adjustment. After rebooting and a couple of adapting cycles it idles at 14.5, but goes rich during decal, wot is also richer than I previously had at 12.1 now. I'm thinking damaged cats and O2s. I'll post up what I find.
Thanks guys...
 
#16 ·
Replaced the front sensor and the readings are much steadier. I'm currently only tuned using the High Idle mod and SC3865 91 tune. It surprises me how good the old girl runs..
 
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