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LTFT way up on Bank 1 means ECU is trying to add fuel, because the O2 signal says Lean.
So, if it really is lean, we have air leaking into that bank, or low fuel flow (e.g. a weak injector or other blockage could do this). Or, it's not really lean but the O2 sensor is sending a low voltage signal. The swap will tell us which option is true.
Great. Will let you know tomorrow once I swap out the O2 sensors.
Swapped out the sensors. Also tightened the air intake hose clamp. P0171 went away but P0130 is now confirmed. LTFT are now 5.47 and 6.25 so I am good there. But I can't tell how to interpret the voltages on the O2 sensors since I swapped them. The are all over the place.
That looks much better to me. A couple questions. Did you clear the codes? Is the P0130 new? It sounds like you had a bad/flakey connection on B1S1 yesterday and swapping them around corrected it. Is the X axis seconds? After about 5 minutes the voltage went way high on the post cat sensors, just like mine did at the 8 3/4 mile mark. The important part is the pre cat sensors are dithering up and down, which is the correct function as the Motronic system richens and leans the mixture in search of stoich.
Yes! Those trends look good! O2 pre-cat voltages dance around (dither, as Ahab says) between about 0.1 and 1.1 volts. The ECU looks for signals crossing 0.4 volts or so, fairly rapidly, as it adjusts fuel trim. That is per design to find optimum air/fuel ratio (i.e. stoichiometric) under changing conditions.
Your trends show occasional dips to zero for both banks, both sensors simultaneously. That could be loose wires or connectors or bad grounds, and be the cause of P0130, because normally the voltage will never reach all the way to zero. Or, as Ahab suggests, it might be a left over from all the messing around with the sensors. Anyway, good progress! You should notice a bit more pep and improved fuel economy, since bank 1 is not being over-fueled now.
Last edited by JohnZo; Feb 26, 2022 at 04:51 PM.
Reason: More information
Fantastic! Thanks guys. Guess it was just a bad connection. I did not clear any errors so it looks like it corrected itself. I will put a multimeter on the wires and see what I can find out but probably later. Right now I am knee deep in coil replacement😩
Just replaced my coils to fix the random misfires I'm seeing. Unfortunately that did not resolve the issue. I have a MAF on order but I am beginning to wonder if I have flaky O2 sensors as the root cause. They were all replaced about 15k but then I had some wire failures on front ones so I bought a replacement NGK one time and a Walker about a month later. So I have a mix of both. Thoughts?
Coming in late to this because I am realizing this apparently was not an easy fix. Couple comments:
1. Front 02's look fine, occasional dips to zero could be normal - are those charts when driving? If you go to zero throttle and the disco coast for a while it will go in to deceleration fuel cut off mode and sensor output will go to zero.
2. If lean codes are present with functioning 02's, then it is lean as determined by the fuel trims. Could be one plugged injector on a bank causing the lean code, check the plugs to see which one is white. Looks like you got your sensors working, still getting the codes?
3. If all you have is the bank two misfire codes at this point but no fueling codes, I suspect plugs, wires, or coils.
Coming in late to this because I am realizing this apparently was not an easy fix. Couple comments:
1. Front 02's look fine, occasional dips to zero could be normal - are those charts when driving? If you go to zero throttle and the disco coast for a while it will go in to deceleration fuel cut off mode and sensor output will go to zero.
2. If lean codes are present with functioning 02's, then it is lean as determined by the fuel trims. Could be one plugged injector on a bank causing the lean code, check the plugs to see which one is white. Looks like you got your sensors working, still getting the codes?
3. If all you have is the bank two misfire codes at this point but no fueling codes, I suspect plugs, wires, or coils.
Hey Extinct - thanks for the reply. I was getting low voltage on the drivers side front O2 sensor as well as lean codes. I swapped it with the passenger sides and the problems "went away" but I don't like coincidence. I am thinking I should replace it even though it is only a couple of months old.
I just replaced the coils with Bosch units so I am going to deprioritize those for now. I have a set of NGK wires that I will try out. What is the conventional wisdom on spark plugs? I have NGK iridium in there now but may start there by replacing them.
Hey Extinct - thanks for the reply. I was getting low voltage on the drivers side front O2 sensor as well as lean codes. I swapped it with the passenger sides and the problems "went away" but I don't like coincidence. I am thinking I should replace it even though it is only a couple of months old.
I just replaced the coils with Bosch units so I am going to deprioritize those for now. I have a set of NGK wires that I will try out. What is the conventional wisdom on spark plugs? I have NGK iridium in there now but may start there by replacing them.
I run Denso platinum plugs. Haven't had any plug issues, I have around 50k on a set.
I'm with Extinct on this one. Those misfires are unlikely to be related to feedback from your O2 sensors, due to the graphs you posted. That's not to say that the misfires couldn't be fueling related, and your very first graphs could have pointed to that, but now that the O2 sensors are cycling correctly I'd suspect ignition or injection problems before the O2s. It's certainly easier to swap the fronts back to their original sides before trying a coil swap but I'd be surprised if that correct the misfires.
