Bottom Line Up Front:
As the cars sits now, the tune is good and nothing is in the RED.
The passenger side side bank is learning to remove more fuel than the driver side for whatever reason.
It is at 68% of its
learned fuel-removal allowance at that light-load operating point. It is removing 8.2% fuel under light load from a maximum learned fuel removal of 12.1%.
It could be for a number of reasons including something from the balance injector discussion from earlier in this post. It can also be a host of other things down to and including O2 sensor mismatch. Below is a list of things to check. Others might have some ideas as well.
The other clue is that the difference between banks got smaller as load increased.
In the
warm, closed-loop cruise log, the median gap between the banks’ learned corrections decreased as raw load increased:
| Raw load | Difference between banks |
|---|
| 10–20% | 5.47 percentage points |
| 20–30% | 3.13 points |
| 30–40% | 1.56 points |
| 40–50% | 0.78 points |
The passenger bank was learning to remove more fuel than the driver bank.
These are
differences in learned correction—not measured AFR differences. Above 50% load, both learned values tended toward 1.000, but that alone doesn’t establish equal fueling; those cells may have had little learning.
For now,
leave the BIN unchanged and keep the car naturally aspirated. Work through these checks and note what you find.
- Save the current tune.
Keep a copy of the exact BIN used for these logs. Record any changes made since loading the supplied file.
- Compare the wideband gauge with the log.
At warm idle and a steady operating point, confirm the gauge and logged AFR agree. Confirm both measured and commanded AFR use the same gasoline AFR scale.
- Record the O₂ sensor history.
Note their age, brand, part numbers if available, and whether both were replaced together.
- Inspect the O₂ wiring.
Check connectors, damaged or heat-exposed wiring, and relevant grounds. Note anything different between the two sides.
- Check for exhaust leaks ahead of the O₂ sensors.
Inspect header-to-head joints, collectors, and sensor fittings. Look for loose fasteners, soot marks, or ticking.
- Check for intake and vacuum leaks.
A smoke test would help check intake joints, vacuum hoses, caps, PCV plumbing, and injector seals. Record the location of any leak before repairing it.
- Inspect plugs and ignition components.
Keep the plugs identified by cylinder and compare their condition. Check plug wires and connections for damage or evidence of misfire.
- Confirm whether the bank difference repeats.
Compare both banks after warmup at matching RPM and load. Preserve the existing logs and learned corrections before clearing codes or resetting memory.
- If the difference persists, isolate the cause.
Compatible O₂ sensors can be swapped side to side to see whether the correction follows a sensor. If injector condition remains suspect, consider professional cleaning and flow testing, including operation at short pulse widths.
- Review the findings before changing fuel values.
We want to resolve the roughly 12.30 commanded versus 12.8–13.1 measured WOT AFR, and understand the larger passenger-bank learned correction. Check fuel pressure if the findings point toward a delivery problem.
Oh... And for Gee Wiz... What bank is your wideband installed and where?
Additional Info I thought was relevant:
This is a comparison of your switching narrow band sensors against the wideband.
| Log | Wideband AFR at passenger narrowband switching | At driver narrowband switching |
|---|
| Warmup—warm portion | 14.663 | 14.665 |
| Cruise | 14.630 | 14.628 |
| Hot restart—closed loop | 14.633 | 14.637 |
This tells me that your narrow band sensors are in pretty good agreement.
Comparison of clearly rich/lean readings during cruise:
- Passenger narrowband and wideband agreed about 93% of the time.
- Driver narrowband and wideband agreed about 77% of the time.
This leads me to believe that your wideband is on the Pass side.
If we can identify and reduce the difference between the banks, we’ll have a better foundation for global fuel adjustments, instead of choosing a compromise between the two.
