Have been looking at $8d AUJP code for the effect of changing o2 related calibration items in Closed Loop (CL). Making changes was beneficial. They will likely apply to MAF engines as well. But, an upfront caution if car has Cats. The effect of some of these changes on the Cat CL feed/starve requirement is unknown.

1. Delay INT Update during Idling/LOW MPH to smooth idle (does NOT affect above Idling/Low MPH)
(Idling/Low MPH is code-defined for 02-related BPW correction purposes as: TPS <= 2.3% and MPH <= 15)
Scalar 0x49A 0 Counts = INT Delay at Idle/Low MPH
Consider increasing the =0 default value. Zero means there will be no INT update delay. Delaying INT at idle will delay BPW corrections, which has the effect of smoothing the idle especially in cammed engines.

CAUTION: The S_AUJP XDF file Conversion formula, and maybe other XDFs, could cause unintended INT delay if not understood. The current XDF conversion is "X/10" and the unit of measure is "Seconds". That means an entry of "1" will delay an Idling/Low MPH INT update by 125ms (1*10*12.5ms). The more correct conversion would appear to be "X" and the unit of measure then would be "# of 12.5ms Counts". After changing the Conversion formula to "X", "8" was used for a 100ms delay (8*12.5) and a smoother idle was realized.


2. Lean-out idle by changing Idle/Low MPH o2 Boundaries and Swing Point:
The Factory AUJP calibration has these settings:
Scalar 0x496 601 mv = FAST o2 Idling/Low MPH Rich/Lean (Swing Point)
Scalar 0x497 601 mv = SLOW o2 Idling/Low MPH Rich/Lean UPPER Boundary
Scalar 0x498 566 mv = SLOW o2 Idling/Low MPH Rich/Lean LOWER Boundary

For cammed engines, consider significantly lowering these values while keeping the Swing Point and Upper Boundary the same. As seen above, GM kept them the same with the Swing Point and Upper Boundary both =601mv, but with a considerably rich-side bias (> 450mv). Proportionately reducing these values will provide larger and more frequent BPW corrections when going-Rich (will go lean quicker), and will provide smaller and less frequent corrections when going-Lean (will be slower to go rich). The result is a leaning-out of the Idling/Low MPH BPW without adjusting the VE Tables.

The following changes were made and the normal fumes during idle were significantly reduced. The increase in INT update delay in #1 above may have also contributed. Based on logged o2 data, there is room to reduce these settings further to Swing/Upper = 400; Lower = 350:
0x496 450 mv = FAST o2 Idling/Low MPH Rich/Lean Threshold
0x497 450 mv = SLOW o2 Idling/Low MPH Rich/Lean UPPER Boundary
0x498 400 mv = SLOW o2 Idling/Low MPH Rich/Lean LOWER Boundary


3. Reduce Prop Gain Counts to moderate BPW (RPM) fluctuations:
Table at Ox4DE=Loop Closed Param, CL o2 Proportional Gain Counts .vs. % Adjusted SLOW o2 Voltage Error
Reducing values in this Table will decrease the magnitude of o2 based BPW corrections, and increasing them will increase the magnitude - the frequency of the corrections will not be affected. In Park at 2500 RPM, my engine would surge with an approximate +/- 50 RPM swing, so it was doing it in gear as well. It just wasn't noticeable. You could hear it and see RPM and BPW changes in a log. I reduced the entire table by 50% and all surging gone! And this is a change that can be safely made with Cats because Counts in this Table are different in every $8d TPI mask.


Totally unrelated to the above, for the longest time was fighting random hesitation at throttle tip from a dead stop and while slightly rolling. Made more AE adjustments than I can count with unsatisfactory results. Finally replaced injectors. Problem solved with smoother idle and greatly improved performance! There are numerous similar problems reported on this and other forums. Replacing injectors with this condition is definitely something to consider.

 

I had the same hesitation, swapping out injectors is what finally fixed it. Thanks for the write up, this is something i will want to try to eliminate odors at idle. I do have fresh catalytic converters, is the worry that leaning out idle will cause the cats to get too hot or perhaps too cold? Im not familiar with the feed starve cycle for cats

 

The main thing is that the cats see a constantly changing rich/lean cycle That's the feed/starve I was referring to. Probably should have been more clear. I can't speak to the conditions the cats will experience, but none of the changes cited stop the rich/lean cycle so should be OK. Maybe someone else could weigh in on that subject. Below is the best explanation I can offer on the need for rich/lean cycle.
And I believe this process also keeps the cats from overheating.

HTH,
Elky

 

The real question is - can you find some settings that will effectively disable the prop. gains? Those of us without cats that would rather target 14.7 like a stand-alone would be able to do would much appreciate this. I'm running EBL but it also has a lot of prop. gain code. I'm assuming inherited from it's original code base as used in $8D and TBI masks that are already speed density. The prop. gains might be great for folks with emissions testing and converters but the idle is hard enough to get sorted out on cars with large cams without throwing prop. gains into the mix.

GD

 

If the proportional gains are zeroed out, the ECM will use the INT to create x-counts. Best bet for idle would be to run it in open loop. This eliminates the short and long term fuel trims along with the prop gains.

RBob.

 

Hi RBob and Tom,

Thank you for your continued support for the 7730 ECM.

Your software knowledge helps a lot of us that are software challenged or do not have the time to dig into the code.

Best Regards,

Bruce

 

Bruce, thanks for the kind words, but RBob has probably forgotten more than I'll ever understand about this stuff
Elky

 

Ain’t that the truth Elky.

Re: Prop Gains, I have found on both my modified (cammed) SD motors, that u really want to reduce at least the Prop Gain at idle. And do so significantly. As an example, the Prop Gain on a stock LT-5 for idle is set at 9. I have mine at 2.
I have done this in conjunction w lowering the O2v values for the idle air flow conditions. I make a much smaller changes for airflow at various part throttle airflow.

 

Yep. Anything in CL idle that will keep the INT from deviating from 128 helps. This has a significant downstream effect because the BLMs distance from 128 will adjust BPW significantly more than INTs distance from 128. And when INT can't move much, neither can BLM. In AUJP $8d, it takes an INT change of > 5 counts before BLM can be changed (always by 2 counts). This is why RBob continues to recommend idling in OL if no Cats because there is no INT or BLM change, and thus no o2-based fueling (PW) change.