Tuning the WOT on a 7730 ECU using 8D approaching 100 VE noticed the PE parameters, PE Change to AFR there are two tables I know they work with each other one is temp the other is RPM there is a formula using the values from both tables to come up with a final AFR. I see that from the factory they are all over the place and was wondering what do the experience tuners do for non stock setups. Similar to the PE Spark advance vs RPM where they zero it out, should I set the AFR vs RPM table in a way where its 12.7 across the board and then adjust the VE table or is there reasoning why it varies from 11.2-12.5

 

Part of it has to do with preventing cat-con meltdown. Sloggy rich cools it and puts it out, so that the brick doesn't melt through the bottom of the case.

RBob.

 

First off, you'll need a WB. Without one, it's pointless to try to tune PE. Preferably wired into the ECM so it can be recorded in Tunerpro (that'll make things easier than trying to un-safely watch it during hard throttle runs). The commanded AFR's may end up being different than the observed actual AFR's.

What some people do is disable PE first, then do some moderate pulls to get the WB data into the 85-100 kPa range. That allows for dialing in the BLM's and VE tables in those high MAP ranges. Just ease into it as you don't want to end up too lean while doing this and damage something. I also richened up my higher MAP O2 thresholds a bit to get good performance-oriented AFRs on non-PE moderate-heavy throttle.... like 13.0-13.5 ish.

Upon re-enabling PE...

I shoot for ~12.5:1 PE AFR's as good rule of thumb as I haven't dyno tuned with my latest setup. But I figure that's pretty a safe and performance-oriented AFR.

With the VE tables dialed in, you can start playing with the PE tables.

You'll also want to enable the switch for locking BLMs to 128 during PE, prior to doing PE tuning. Theoretically if your BLMs are close to 128, then this shouldn't matter. But without this switch enabled, I believe what happens is (if you enter into PE with a BLM >128), the ECM will richen up your commanded PE AFR's by a proportional amount (which I think was a safety feature). But you don't want the ECM interfering with your tuning in this case.

 

I like to think of it like this:

The 22.66% coolant temp compensation (along with the 14.73 stoichiometric ratio) sets up the base PE target AFR (12.0:1). The rpm table then allows for fine tuning up or down (+ rich/ - lean) from the already established base PE target AFR in order to fine tune the target. Set the rpm table to zero if you want 12.0:1 across the board.

I like to use LV8 instead of rpm to modify the base PE target AFR.

 

what do yo mean LV8

 

Here's some information on PE for '7730 and OEM style BIN (not S_AUJP)

PE will come on based on TPS and MAP.

1. MAP is set with "Enable minimum MAP for PE" (0x55F)
2. TPS is set with table "Enable %TPS vs RPM (0x603) or "Enable %TPS vs RPM when high CT" (0x608).
3. High CT threshold is set with "Min CT For High CT AFR > " (0x602)

When PE comes on, INT will lock at 128, BLM will lock at 128 only if under 128. If over 128, BLM will keep its value associate with BLM cell. That's why it's important to set BLM boundaries in line with MAP PE trigger. You want to dedicate the last 4 BLM cells (12-13-14-15) to PE. That way, BLM is always locked at 128 and you get more consistency with real PE AFR (what you would read on a AFR gauge). The 128 lock feature is only available with S_AUJP BIN.

From experience, I never tune WOT VE with PE disabled. I lock Commanded PE AFR at 12.5 across the board, dedicate BLM cell 12-13-14-15 to PE WOT and go conservative on VE value (rich). I then tune VE directly to get to 12.5 using AFR gauge that can be datal logged. MAT readings can affect real AFR at WOT because the ecm will compensate for intake air temperature. Leaner when hot, richer when cold (that can be tuned also).

On high performance engine with TPI intake style, VE can reach as high as 120%. VE table is maxed out at 100%. To deal with this, you can lower injector flow rate by, let's say 20% and decrease entire VE table by 20%. You will obtain the same injector BPW calculation. In other words, a 20% decrease in injector flow rate requires a 20% decrease to VE table. This will yield a gap of 25% in VE table. If VE is maxed out at 100%, it will lower it to 80%.

PE commanded AFR is calculated this way: Commanded AFR / (1 + (%Change vs CT/100) + (%Change vs RPM/100))

IF (example),
Commanded AFR = 14.73
PE Change to AFR vs CT is 18.4 at 176Deg.F
PE Change to AFR vs RPM is -3.1 at 4000 rpm
PE AFR = 14.7 / (1+ (18.4/100) + (-3.1/100)) = 12.78

To estimate Real AFR with a narrow band O2 sensor at WOT:
830 mv = 13.0:1
880 mv = 12.5:1
930 mv = 12.0:1
Ultimately, you want to use a AFR gauge and tune with a chassis dyno.

 

'7730 $8D does not use LV8. You are talking about MAF system not MAP.

 

Great info what I was looking for but one thing I dont get, "dedicate BLM cell 12-13-14-15 to PE WOT", where is this parameter in 8D?

And when your are saying "I lock Commanded PE AFR at 12.5 across the board" your talking about what I mention, editing the PE Change to AFR vs RPM table in such a way to get 12.5 all the time for example using that formula with the stock bin that has 22.6% change during operating temps so just setting the whole RPM table -5.00 will yield 12.49 across the board

 

My explanation were not clear indeed. Reason is, it's not easy to explain

Here's an example that worked for a certain application. ATNX is OEM tune and SB_S_AUJP383 is a custom tune. The BLM cells were redefined to better represent engine load map. Cell 12-13-14-15 were dedicated to PE. PE MAP threshold was set at 90kpa. This is just an example. You can set your MAP PE threshold lower if you want PE to engage earlier. As long as you match the BLM cell boundaries to isolate 12-13-14-15 for WOT.



Be aware that the X, Y axis are inverted in VE tables. So RPM is Y and MAP is X. Representation is more like this:



You'll find the boundaries in tables 0x513 & 0x510 Cell boundaries


Yes!

 

When tuning WOT PE, keep in mind that 1980's GM EFI systems are antiquated and not very accurate. They were not designed for high performance accuracy. You can only modify VE by +/- 0.4 increment. Also, if you observe your real AFR (on gauge) off by a certain percentage, you might want to divide the percentage by 1/3rd for your adjustment. Otherwise you'll end-up chasing your tail. If you want 12.5 and you bounce around 12.1 to 12.9 on the gauge, this is as good as it would get. Don't fall into the "obsessive trap" of being perfect.

FYI: gas quality, ethanol content, engine temperature, voltage, barometric pressure, intake temperature, ambient air temperature and humidity will affect real AFR. ECM can only compensate for air intake temperature and voltage but it is not accurate. So make note of these parameters every time you data log so you can have some sort of comparison. I like to tune on an average summer day. For us around here, it's 75Deg,F with 103kpa baro, 60% humidity. Once the tune is locked in, I will do some testing in cold (25Deg.F.) and hot weather (95Deg,F). Depending where you live and when you drive, your tune might need a lot of work to compensate for temperature extremes. Sooooo.... don't be surprised if the real AFR varies from one day to another.

Peace

 

I think what you're asking hasn't actually been answered, the explanation as to how it derives to the final value was properly demonstrated above, but I think what you are asking is why the stock values seem to be not quite as linear from start to finish, correct? You need to remember that the factory bases the overall and predetermined tuning on the VE table. The other parameters work in tandem with one another to arrive towards a final value. They change because the needs of the engine change, eg; more fuel needed when cold thus a larger percentage commanded if PE is triggered, more fuel needed off idle from dead stop, or cruise, thus more of a percentage is commanded in the area, and these areas of when and how much are based on final gear ratio and VE. If you set the percentage to what you think is a constant 12.8 AFR by using a higher percentage value then you are assuming the cam characteristics and cylinder head cfm flow does not deviate from start to finish, when it does. These values that you posted from the factory have already taken all of this into account before leaving the factory, mind you not as precise as when using a wide band like today, but close enough. Bottom line is you're balancing the fueling of your engine, not to mention when this is altered via modifications then your timing needs to match such changes in conjunction with AE/PE changes. When I look at the picture of the PE values you posted above, I don't see values all over the place, I see values tailored to a specific factory engine demand. Hope this helps...

- Rob

 

The 22.66% coolant temp compensation (along with the 14.73 stoichiometric ratio) sets up the base PE target AFR (12.0:1). The rpm table then allows for fine tuning up or down (+ rich/ - lean) from the already established base PE target AFR in order to fine tune the target. Set the rpm table to zero if you want 12.0:1 across the board.

 

somebody Ban this copy paste account.