Brand New NBO2. 7730 ECU

What have the experienced tuners done when the WBO2 readings are contrary to the BLM History in some cells. Seems to me that if you tune to the WBO2 in closed loop, the BLMs will never fall into place at 128 or so

See photo of recent data log.

 

The wideband will read the same as your short term fueling if the correction limit is within reason. If, say, at idle, your BLM is 120, but your INT is steady at 128, it is telling you that its' correction is within reason, so your wideband will read stoich. The idea then is to reduce the O2 correction span to increase the BLM, and you do this by Leaning out the VE in that area, not because you are too Rich, but because you will want as close to 0 percent O2 correction as possible, and for good reason as it effects other areas in your fueling...

- Rob

 

I think what I am understanding is that I need to Tune the VE table to the BLM history. For example, on the attached chart I sent the BLM in cell (1000 rpm/40MAP) is 124.69. Rich condition, pulling out fuel. The WBO2 reading for the same cell reads 15.115, Lean. What I need to do is lower the VE that cell to raise the BLM. The WBO2 should stay about the same assuming the INT was tracking at 128 (or close)

On Base?

 

Think of it this way... the NB knows stoich. That's about all it knows. The correction and offsetting percentage swing is limited to the ECM you are using. In the above example I gave of a 128 INT and 120 BLM resulting in a wideband reading of 14.7 AFR. However, if, say the INT was reading 130, and the BLM were reading 119, then the wideband would be reading a tad Richer than 14.7 AFR because the O2 correction went over its' limit, and its pulling fuel. Just make a mental note of, or write down the RPM/kPa where you are seeing any deviation or discrepancy, pull up the graph in Tuner Pro, and Lean out while smoothing the VE in that specific area. You can of course use the cell chart and multiply the correct value to make the same reduction, but you would find yourself going into the graph and smoothing it out either way, so why not just go straight to the graph. Keeping the VE as close to a 0% correction as possible throughout the VE will allow for the INT/BLM to both lock closer to 128 whenever you enter Power Enrichment, which is important. You can peg the PE to allow yourself to tune the entire VE table without interruption of PE to maintain a 14.7 AFR while dialing in a 0% correction throughout, or you can keep the PE values where they are and use the wideband to essentially do the same thing even when PE kicks in by using it's AFR values.

- Rob

 

Rob

Correct me if my interpretation of what you have stated is wrong. The GM design is that when the tune has achieved INT of 128 and BLM of 128 (in a particular RPM/MAP cell) the AFR in that cell will be 14.7. In theory, the WBO2 should confirm those results.

If the tuner, for whatever reason, wants to change the AFR (for example, different fuel), they have to change the target voltage for the NBO2. That is done by changing the O2 Swing Point. Increasing the voltage of the O2 swing point will lower the AFR.

 

Are your WB and NB on the same side of the engine?

 

Yes to the swing points which has been a topic of much discussion here when tuning for cams with greater overlap. In the LT5 cals, at least, I can change the stoich value which allows for the use of fuel w differing levels of ethanol. Pretty sure other cals do the same.

 

This has been a interesting, but vertical learning curve for me. This is a 25 year old build that lost the engine due to a roller lifter eating a lobe on the cam after 85k miles. Replaced the 1995 era 502 marine engine block with the new ZZ502 short block. Cleaned the injectors, rebuilt the Brodix heads. Started the engine the first time and you needed a gas mask in the garage. Significant CAM differences between old and new. Been chasing a tune since, but getting close. The resources provided by the members of this forum have proven invaluable to me.

With regards to the O2s. The NB is on the passenger side about two inches below the collector on the shorty headers. The WB is the same side about 12-14 inches further down from the NB (about 21-22 inches from the Exhaust ports on the head). The WB is calibrated per the Moates formula in Tunerpro.

I have attached my O2 Swing points and boundaries. I believe them to be set for about 14.5-14.6 AFR (based on the discussion on this forum). I am in SW Colorado at about 7.500 feet, so MAP craps out at about 75.

 

When you have an average of a 128/128 INT/BLM (at any given point in time during Closed Loop), this is telling you that the ECM is achieving this at a 0% correction rate at that moment. The older systems have an O2 correction rate of about 6%, so provided that the fueling is not 6% or higher in terms of being too Rich, or too Lean, the system will average 14.7 stoich regardless. So if you see an INT of 128 and a BLM of say 125 at one point in time, or 131 at another point in time, the system is still averaging 14.7 stoich regardless.It's only when you see the INT move when you have reached the correction threshold in either direction. But we are talking Closed Loop here, which is being corrected for. However, when you enter into Open Loop and Power Enrichment, there is no O2 correction, and this is why you want to average the VE at close to 0% correction in every cell. Example, do you see how the Open Loop and Power Enrichment tables have predetermined AFR values? Now, if you wiped your VE table(s) clean by making them all 0 value, do you think the system will know, automatically, how to reach those AFR values? Absolutely not. Those AFR values use the VE stoich values to calculate the amount of fuel needed to derive their target. This is why you will want as close to a 0% correction as possible with the VE table. So, even though you may see a 14.7 AFR on the wideband, but see, say, a 128 INT and 131 BLM on the narrowband, when Power Enrichment triggers, you will be Leaner than your 12,8 AFR target because you were averaging stoich in Closed Loop via O2 correction, despite seeing 14.7 AFR on the wideband....

- Rob

This depends on which system you are using. All O2 sensors are Lambda based, they are then calculated to the fuel you are using to make it easier for the tuner to digest through AFR. Ideally your tuner does not have to change anything, he or she would just need to compensate for the correct percentage needed if the AFR value is different than pump gas. E85, for example, needs 30% more fuel than gasoline. Without changing anything, simply fill the tank up with E85 and watch the BLM go Lean. Increase the VE by 30%, and watch the INT/BLM settle closer to 128/128 at 14.7 AFR. However, the key here is that the stoichiometric value for E85 is 9.73 AFR, yet the system will still reflect a14.7 AFR and 128/128 INT/BLM, and this is because all O2 sensors are Lambda based...

- Rob

 

Educational.

In Open Loop / PE mode, to correct the VE tables, it sounds like you need to disable the PE mode. I have two tables. One enables PE at 50% TPS (1200 rpm) and the second one enables PE at 60% TPS (1200 rpm) when hot. I cannot find the hot temp defined (must be someplace else).

I assume I can move the "enable" TPS threshold up (to 80% for example) and get some data based on Closed loop/ no PE for setting VE in those cells?

 

Here's my 2 cents worth. After extensive, and I mean EXTENSIVE hours of data logging and analyzing all that BLM/INT and WBAFR stuff.

IT'S INNACURATE!!!

An here's why:

Each BLM covers a large area with multiple cells. An average BLM of 128 could have extremes at both end (lean and rich). Averages mean nothing without analyzing the max/min.
But it's hard to analyze min/max because some BLM# get carried over to another BLM when ecm goes from one BLM to another.
Low count in a cell when data logging creates irrelevant averages, specially when multiple low counts add up to higher count.
The BLM rate update is slow enough that the BLM adjusts after the fact. Good luck with that one!!!!
Some BLM numbers get recorded in the wrong BLM# when it's near the BLM boundaries. (that's a pain!!!)
TunerPro does not establish BLM boundaries like the ECM does. This creates discrepancies in reporting.
Yes there is differences between WB AFR reading when in close loop. Sometimes the NB sensor will read stoich and WB will report richer than 14.7!!!! That is the limitation of early GM EFI... basically inaccurate.
WB AFR Gauge seems accurate at WOT.
BLM can vary greatly depending on engine running time, MAT heat soaking and air temperature. Comparison can only be done with all things being equal (MAT, Voltage, Baro, Outside air temperature and humidity).

I now tune with INT only. I have disabled BLM and Proportional Gain. I also disabled stay alive (stored BLM). It seems more accurate when tuning and open loop is now constant.

AND.... that's not the only thing that is not accurate:
There could be differences between SA user input and real SA at balancer. (Good luck with that one also)
RPM reporting is inaccurate at higher RPM (4000-6000)
Stay Alive can detune open loop with stored BLM
WB AFR are usually reporting AFR numbers based on stoich for gasoline. If Ethanol is present, numbers are inaccurate.

Bottom line is don't except too much from this ancient 7730 technology. It is inaccurate and can drive one crazy.

I am personally done with it. Next project is going to have a modern EFI and software with self learning capabilities.





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Your WB IS reporting accurate AFR if u use Lambda.My ZT-2 provides Lambda altho it shows 14.7 AFR. However, my cal is set to 14.2-14.3 for the 10% Ethanol we have here in the Midwest.