Hello. I am new to these forums and am trying to track down why my truck is not running as it is supposed to. I have a scanner connected to it while it is running and it is showing bank 1 sensor 2 is at 99.06% fuel trim. Sensor 1 moves around but stays between -5 and 5. Sensor 2 shows voltage but the trim just sits there at 99.06 and doesn't budge. Tried disconnecting the battery hoping to reset the ECU's settings but that didn't help. I had a broken up catalytic converter. Replaced that and then found a vaccum leak. Fixed that but it is still stuck at that value. Any thoughts? Thanks in advance.

 

Sorry forgot to put in what truck I have. Its a '98 5.2 4x4 stock.

 

Does the scanner show the voltage readings? If so what are they.

What kind of emission system do you have/How many sensors do you have?

 

It is the stock emissions system. The voltage moves around. It goes as low at .100 but can go as high as 1.000. I will check it as soon as I get home again and post more exact readings.

 

I was trying to figure out if you have Ca or Fed emissions. Fed has two o2 sensors. Ca has four. Both .1 and 1 seem out of range. I have never seen orheard of fuel trim that high. I think maybe you have the scanner on the wrong setting. If you have federal emissions, bank 1 sensor 2 has nothing to do with fuel trim. Are you looking at short term fuel trimandlong term fuel trim maybe? Even so ltft at 99% and stft staying correct (alternating from -5 to 5 and points in between is normal) seems odd. Usually anything over -/+ 32 ltft will throw a rich/lean code respectivelyin a short period of time.

 

Ok. Sorry for the misunderstanding. It has 2 O2 sensors, not 4. Here are the readings I am getting at idle:

B1S1 trim: bouncing between 0 and 8
B1S1 volt: bouncing between .150 and .900
B1S2 trim: 99.06 static
B1S2 volt: bouncing between .100 and .800
STFT: bouncing between 3.00 and 10.00
LTFT: -9.36 static

Bad sensor maybe?

 

Here is another piece of information, not sure if it will help you or not.

With the engine off and ignition in the on position, all the trim readings are 0.00 except for B1S2 which still reads 99.06 and both sensor output voltages read 1.000 static.

 

.8 is in range- .1 still seems low, but is probably alright. Your fuel trims are almostperfect. I am not sure how your scanner reports, but I think the number you are looking at might be giving you the calculated efficiency of your catalytic converter.

 

Ok. Its a new cat. Should I do something to try to reset that 99.06 value or is it good as is?

 

I would leave it alone. I guess you want to see 100% efficiency and ruin the curve for the rest of us