ChemEggXj

Hey everyone, hope you could help translate some data from scan tool. I have a 2000xj with about 160K, in past three years have replaced all plugs, fuel injectors, and O2 sensors. Two weeks ago, I got a code for a non performing Bank 2 precat (california emissions). I knew it was time to change these as they were the original and considering the state of other exhaust components, I opted to do a manifold back replacement. I few days after getting my rig back from the shop I throw a P0174. Ive had this in the past but it was from a leaky fuel injector Oring which once replaced solved the issue. I have the live data and if someone could help me understand whats goin on I would be very grateful.

Prior to the below values I noted tested my B2S1 O2 sensor and saw that the O2sensor output voltage was zero. At the pins on the harness side there was voltage and a good ground at the pins so I figured that the O2 sensor was bad and replaced it with a NTK. I rechecked the data and it was cycling but the P1074 code was still there. The data below now shows that the B2S1 and now the B2S2 O2 sensors are not cycling. What is going on ☹ they were both working yesterday now no voltage to the new B2S1 O2 sensor and the B2S2 is stuck on 1.0V.

Calculated load: 5.1%
Engine coolant temp: 90 Celsius
Short term Fuel Trim- Bank 1: -1.6%
Long term Fuel Trim- Bank 1: 2.3%
STFT Bank 2: 32.8%
LTFT Bank 2: 32.0%
Intake manifold absolute pressure: 43.0kPa
Engine RPM: 672/min
Ignition timing advance #1 cylinder: 10 degrees
Absolute throttle position 14.5%

O2 sensor output voltage B1S1: 0.120V (it is cycling)
STFT B1S1: -1.6%
O2 Sensor output voltage B1S2: 0.440V (it is cycling)
STFT B1S2: 99.2%
O2 Sensor output voltage B2S1: 0.00v (not cycling)
STFT B2S1: 32.8%
O2 Sensor output voltage B2S2: 1.00V (not cycling)
STFT B2S2: 99.2%


Thanks in Advance

tech

To me it looks like B2S1 is not working . I would change the 2 o2 sensors next to the exhaust manifolds

Dave51

or

Dave51

Your scan tool takes the mean reading so doesn't tell the whole story, but S1s should be about 0.6V and S2 about 0.4V. It looks like B1S2 is the only one working correctly.

Dave51

Do you have any pending codes? Seems to me there should be a bunch of P014x codes (although I suppose it doesn't really matter).

What's a "manifold back replacement"?

I'd also be checking wires.

ChemEggXj

Thanks for the reply’s! I really appreciate all the input and the great graphs. So the B1S1 and B1S1 are cycling through the correct voltages…. The B2S2 was cycling correctly two days ago then now it’s stuck on 1V. The B2S1 was just changed 48hrs ago due to a zero voltage reading and now the new one is as well I did check the pins on the harness and was getting voltage and a good ground. “Manifold back” means I’ve changed the manifold back to the tailpipe…. All new. S it really possible that both O2 sensors on my B2 just went bad…. Including a new one. I was thinking that I have a huge leak at the manifold but it’s a solid one piece Banks, it would be leaking at B 1 as well. I have no other pending codes but will check again on the way home from work. Thanks again !

tech

OK the B1S1 and B2S1 are the sensors that the computer uses to adjust the fuel the engine gets the S2 sensors are there to check how good the catalytic converters are so I would stop looking at them until you fix the S1 sensors problem and you should be able to get the O2 sensors to go up to .90 volts just under 1 volt if you can't get it to go that high by revving the engine , the sensors are not working good

Dave51

Actually, starting in 2000 the S2s do participate in the AFR calculations:

From the SM:

ChemEggXj

Dave51 and tech, thanks for the reply. I really appreciate your time and the SM information. Ive been working late so did not get a chance to respond. All I heard is that the downstream sensor does not participate..... apparently thats not true. good to know! I did take it to the local shop just to have them confirm the data above..... they read the live stream and are in agreement that the B2S1 is not working and is the first place to start. They did not check the pins on the harness side, but oh well. They recommend new O2 sensor and see if it goes into closed loop then. What I will do tomorrow ( I have off) is replace the B2S1 with another NTK and see if it finally does any good. I did note that when my key was in ACC that i did not get any voltage read from the O2 sensor warming pins on the harness.. 0V. I checked fuses and everything is ok. Does the O2 Sensor warmer only get voltage when the car is on???? Another problem that this could be. If none of this works then I will inspect all the injector o-rigs to look for tears and such. Guys at the show said all the manifold bolts and intake were secure. Thanks everyone!

ChemEggXj

Problem solved! so Dave51 is right, the downstream does affect air:fuel in my 2000xj. Exchanged the B2S1 and changed the B2S2 and now all the STFT and LTFT are in working order, all voltages for O2 sensors are cycling appropriately. I think originally that only my B2S1 O2 sensor was bad but then when that failed completely my B2S2 also went bad. Replaced both of them and problem gone. Next step would have been to either smoke test or pull the fuel rail and inspect the Injectors and injector bushings. Instead I'm going swimming and gunna drink a few wobble pops. Thanks everyone, happy 4th!

Calculated load: 5.1%
Engine coolant temp: 90 Celsius
Short term Fuel Trim- Bank 1: -1.6%
Long term Fuel Trim- Bank 1: 0.8%
STFT Bank 2: 0.0%
LTFT Bank 2: 0.0%
Intake manifold absolute pressure: 41.0kPa
Engine RPM: 699/min
Ignition timing advance #1 cylinder: 11 degrees
Absolute throttle position 14.5%

O2 sensor output voltage B1S1: 0.820V (it is cycling)
STFT B1S1: -1.6%
O2 Sensor output voltage B1S2: 0.260V (it is cycling)
STFT B1S2: 99.2%
O2 Sensor output voltage B2S1: 0.460v (it is cycling)
STFT B2S1: -0.8%
O2 Sensor output voltage B2S2: 0.480V (it is cycling)
STFT B2S2: 99.2%

ChemEggXj

I take it back, still throwing that code P0174. I now have no idea. Anybody on LI want to but a jeep?