O2 Sensor Voltages

[ccernst]

I've posted this question in a few other Ranger forums with little success, thought I might try here.

I got a Ranger about a year ago and love it. It is a '98 Ranger SuperCab 3.0L 4x4 manual. The owner before me tried to take care of it, but the mechanic she took it to was taking her for a ride I think. When I got it, it ran very bad. I did a pretty big tune up on it and it runs pretty good. But I do have one quirk.

I have no CEL on, but when I hook my Acctron 9180 scanner up, it reads the following:
o2s11 0v
st ftrm11% ranges from -1.0 to 0.8
02s12 0v
st ftrm12% -100.6 solid
o2s21 0v
st ftrm21% ranges from -2.2 to 0.0

I made these readings after a 20min drive home from work. My fuel trims are at extremes.

Anyone run into this?

[J-Ri]

Originally Posted by ccernst

I've posted this question in a few other Ranger forums with little success, thought I might try here.

I got a Ranger about a year ago and love it. It is a '98 Ranger SuperCab 3.0L 4x4 manual. The owner before me tried to take care of it, but the mechanic she took it to was taking her for a ride I think. When I got it, it ran very bad. I did a pretty big tune up on it and it runs pretty good. But I do have one quirk.

I have no CEL on, but when I hook my Acctron 9180 scanner up, it reads the following:
o2s11 0v
st ftrm11% ranges from -1.0 to 0.8
02s12 0v
st ftrm12% -100.6 solid
o2s21 0v
st ftrm21% ranges from -2.2 to 0.0

I made these readings after a 20min drive home from work. My fuel trims are at extremes.

Anyone run into this?

O2s11 is bank one upstream sensor
O2s12 is the only downstream sensor there is
O2s21 is bank two upstream sensor

I'm not familiar with that scanner, but if it is a lower cost one, I wouldn't necessarily trust it for the voltages, get an oscilloscope and look at what the voltage actually is. The STFT will usually read near 0, as it will "pass" the counts on to LTFT if it stays above/below +/-10%. Will that scanner show LTFT? I'd be more concerned about that than STFT. Those STFT numbers look very good. +/- 10% is where you want it to be, it's no better to have it at 0% than it is the have it at 8%. I have not been able to try it, but I've been told that if you check a brand new car it will read a few % away from 0. You might want to take it to a shop that does the BG induction flush. I have seen that get the FT closer to 0 many times, it also cleans up the O2 sensors a bit, but generally if the sensor's bad it's bad, you're not going to fix that with chemicals.

For the B1S2 STFT -100.6%, that's not a valid number. The maximum is 100%, and the SES light should illuminate at (I think) 20% for any FT number. I think you probably have a computer problem, either the scanner or the PCM. If it's a cheap scanner, I'd suspect that first. If the O2 sensor voltages were actually 0v, you would have a code for each one, and quite possibly multiple codes for each one.

[ccernst]

The scanner is able to read live data, so it isn't the cheapest unit on the market. It does not give LTFTM...it goes through a process where it checks for a possible 109 values...then starts reading what it can.
My cousin runs his own mechanic shop and has a real scanner where it can run diagnostics against the various computers...he said all of them passed.

I get to change out my radiator, so while I work on that, I'll see if I can get my computer code and see how much a new computer is.

[ccernst]

Bit of an update. I've recorded some data with the scanner, here is what I've recorded. Each reading is about .5 seconds time.



Edit, this is a bit from the manual that describes the difference between "ST FTRM1%" and "ST FTRM11%"

ST FTRMxy (- 100 – 99.22%)

Short-term Fuel Trim Bank calculated value represents the short-term relation of fuel metering
on a fuel-injected engine.

✓

Short-term Fuel Trim calculated value that has a positive percentage is a rich
fuel trim and if a negative percentage is present the fuel trim is lean.

ST FLTRMx (- 100 – 99.2%)

Short-term Fuel Trim value represents the short-term relation of fuel metering on a
fuel-injected engine.

✓

Short-term Fuel Trim value with a positive percentage is a rich fuel trim and if
a negative percentage is present the fuel trim is lean.

[njranger]

Just saw this and registered because I'm seeing the exact same thing;

O2S11: 0
STFTRM11: -1
O2S12V: 0
STFTRM12: -100.6
STFTRM21: -2.2
O2S21: 0


Just wondering, did anyone solve this?

[DonSor]

I was told that after a while (90 or so thousand miles in my case) the O2 sensors start to become "lazy", not bad enough to trigger CEL but slowly deteriorate to a point whereby it no longer sends the correct signal thus affecting engine performance. I got a '99 4.0L Ranger and instead of going to trouble of measuring voltages, etc. I just decided to replace the two pre-cat sensors and also the post-cat sensor with NGK O2 sensors.

[ccernst]

I've given up on it. Truck runs fine and get comparable gas mileage to other rangers with the 3.slow.

One of my sensors was replaced...still shows 0v. Whatever.

[toddler62]

180k miles on my 94 Ranger . Has original o2 sensors and get same miles per gallon as it did when new.

[njranger]

thanks for the replies! Yeah- my Ranger is still running great so I'm not really concerned anymore~