Aldl Readout, Does This Mean My O2 Sensors Are Shot?

grosss · January 27, 2008

Ok, so I made an ALDL Cable (93 Silverado, 5.0L, 459,000kms :-) original everything I think...) and read in the data from the computer to see how my engine is performing using TTS Datamaster.

Long term BLM data is showing that for most of the time it's rich at some rpms/MAP, lean at others, and the fuel trim cell number is bouncing around like crazy. the LTerm counts are around 112 and the box turned red, and STerm counts are all over the place. Watching my O2 sensor voltage, its bouncing all over the place, usually between 40-50 and 800-950mv.

I have a feeling this is saying my O2 sensor(s) are shot, but I have no idea what the data would look like for a perfectly happy engine, so I'm not sure. I'm getting piss poor fuel economy and hoping this will give me some insight into why.

I thought the fuel trim cell number is supposed to stay at 0 or 1 most of the time? I'm seeing 4,5,6, 9,10,14, and 18 at warm idle.

Any thoughts?

grosss · January 29, 2008

Ok, so I took a look at the Datamaster results again, I let the truck idle for a good while after it was warmed up and in closed loop, and the STerm was hovering around 128, bouncing up and down every so often, but the O2 Sensor voltage is like 50-80, then suddenly 200, then 850-900mv, kind of cycling through that, and the "rich/lean flag" is on most of the time.

RPMs are somewhat constand at 650, bouncing up to 675 sometimes, and less often falling to 625.

Does anyone have any insight into this, or other places to look to see why I have horrible mileage?

fixitmann · February 2, 2008

Its normal for O2 sensor readings to "bounce" around. It is referred to as switching.If you would like more info on this Pm me and I will share some of my waveform library of known good and bad readings.