I am reading to understand how the Barometric adjusted VE influences my VE table settings and how they will act as I change elevation. $8d S-AUJP-V7. Using the V7 EDX and ADX files BIN. Naturally aspirated.

My settings seem to agree with the Read me First document provided with V7 other than ALDL word 30. It is set for EGR duty cycle versus 002E for Barometric Pressure. Is this just a reporting value?

Don

 

Barometric pressure affects the exhaust back pressure. Less back pressure the greater the engine VE.

I could see how exhaust back pressure could affect the EGR. Less back pressure, less EGR gases make it into the engine.

RBob.

 

Let me explain where I am going with this. I apologize in advance if my questions seem dense on my part.

1. I live at 7.600 feet. WOT here is about 75 kPa or so. I am attempting to tune the engine so that is performs well, both at Colorado elevations, but also at sea level to !,000 feet elevations. I have noticed several instances when doing test runs where after the first run, for example, I am lean BLM History Table. I use the BLM/128 method of arriving at proposed changes to the VE table. I make those changes. The next run a day or so later, I am now on the rich side. I originally was using manual and automatic "smoothing" and attributed the "overshoot" on the VE adjustment to the smoothing process. The last few times, I have abandoned smoothing (at least for the time being) only correcting a few obvious dips or peaks (in the graph).

2. I recently upgraded to Version 7 S-AUJP (with some hiccups). I started clean with all new BIN, ADX, XDF, because what I had before was leftovers from someone else's tune. I am now pretty close to having a clean tune. There are a couple of weird, unexplained knock retards at 1200-1400 that I decided to ignore for a while. The BLMs are close, but some issues at low RPM and low MPH where the history table doesn't follow the BLM on the Dash board or monitor. The history table is averaging over a longer period.

3. I recently added the BARO-Adjusted VE to the dash board. With that, you can see a VE type value to compare to the VE Table for that specific MAP/RPM cell. Of course, the value is different than the table because of the BARO adjustments. I start questioning if a change in Barometric pressure is contributing to the undershoot/overshoot issue as noted in Item 1. As I read the various parameters, the changes to the VE Table due to changes in BARO are based on tables. Like tuning the VE Tables, I can see that the BARO tables will likely need to be tuned based on results.

4. My question about ALDL word 30 was to see if the actual Barometric pressure was something that could be read by the ECU and the value noted. That way, a change in BARO from one test to the next would be a known factor. The EGR % Duty Cycle is discoverable on dashboards or monitors. If checking the box in word 30 provided a Barometric pressure value that could be recorded, it would make sense to check it.

5. My car is homebrew in a 1938 Chevy Coupe.. Basic ZZ502, TPI from Street and Performance, 7730 ECU, garbage wiring harness from Street and Performance from sometime in the 80s, short block hugger headers, Borla mufflers and out the back. No cross over. No EGR or any other such factory smog inventions.

Let me build a hypothetical question. I think BARO changes at one location are not all that problematic. You are just dealing with weather related changed in high and low atmospheric pressures. But, changes in altitude are more long term. Assume I have the car perfectly tuned for 7,500 feet. VE Tables are producing 128 BLMs across the board. I drive the car from 7,500 feet (Baro = 75 kPa) to sea level (Baro=100).

a. What changes would I expect to see in the tune (BLM History)
b. Assuming there are changes, can they be mitigated by properly establishing BARO table values.

Don

 

I don't see any reason that the ECMs barometric pressure value can't be in the data stream. It would be helpful in tuning in the pseudo baro read that the ECM does. At key-on the ECM reads the MAP early on and saves it as the current barometric pressure.

Then as the vehicle is being driven a pseudo barometric read is done and the ECMs baro pressure is updated. SAE paper 1999-01-0206 describes the process (publicly available paper).

RBob.

 

Will address a couple of things here and the others later. But before doing that, would appreciate your posting a .csv log that contains a drive at 7500 ft and at 1000ft, and with travelling in between if possible. Of course you'll need to identify the log sample numbers, or start/end times, during which each activity occurs. But before doing that, see below.

The BARO table at 0x6C7=BARO Param, BARO Pressure .vs. RPM .vs. TPS can be changed, but changes may not provide the results envisioned (more on this in a later post). For now, VE from a table is adjusted based on a Factory GM formula utilizing BARO. BARO is determined at key-on as the larger of the value at prior key-off and that at current key-on. Then for normally aspirated engines, BARO is updated 10 times a second while running. But the conditions required for that update are fairly stringent (will provide details later). So for now, just know that BARO for NA engines can be adjusted while running, but may not occur unless a certain set of conditions are met. So don't be surprised if you don't see a change, or if the change is small.

Apologies for an XDF error, but ALDL Reporting Scalar #30 is improperly titled. This error and will be corrected and posted.
The correct title should be "EGR % Duty Cycle" which agrees with the address in the Scalar of "0123".
Given the title is currently "Barometric Pressure", to report Barometric Pressure, just change the address of #30 from "0123? to "002E".
Will also need to change the title in the ADX file from "EGR % Duty Cycle" to "Barometric Pressure".

VE from the Tables can also be reported so it can be compared with BARO Adj VE. If you're already doing that, OK, If not, change the title of ALDL Reporting Scalar #26=SC1 INPUT STATUS Bits to "VE from Table" and change the address from "0030" to "01C6". Here, a new ADX Value will need to added with title: "VE from Table" and with Packet Offset =26 decimal.


More later once you post a log. Please also post the BIN that used to create the log.

Elky

 

I have Baro Adjusted VE reporting. Stepping through the samples let's you see the variation between the VE table and the Baro adjusted VE. Probably a history table would be valuable.

I changed over the ADX Value as well. Other than the title, any other change to the ADX Value necessary??. I guess the measurement is "kPa" when it's reported.

I added my latest ADX dashboard. You can see the Baro Adjusted VE and the Barometric Pressure in the lower right.

I tried to test the Barometric pressure without starting the engine. Just read zeros.

 

I didn't reply to the attitude logs. To have logs from 7,500 feet and 1,000 won't be available for comparison for some time. That would require a trip from SW Colorado to Scottsdale or Tucson. None anticipated soon.

That being said, we are relocating from Pagosa Springs, CO to Williamsburg, VA (Elevation 82 feet ASL) over this coming winter.

For a longer term analysis, a CSV from 7,500 feet could be compared to the CSV at 82 feet. The test at 82 feet using the same BIN, etc. Probably be December before that could be had.

Don

 

Yes, change ADX Units Display to "kPa".

Regarding other reporting, do this:That way you'll have both VE from the table and the BARO Adj value in the log to compare to see the actual adjustment.

That should not be. Did you change the address of #30 from "0123? to "002E"?
Please zip up your bin, adx and xdf and post. Tks.

 

Understand.

 

I got something wrong. I am getting a weird number for VE from the Table. I think I don' t understand the "packet offset = 26 decimal"

Attached

Don

 

BIN ADX XDF

 

Will review. In the meantime, some light reading .

My comments about BARO Adjusted VE et-al. Detailed, sorry.

1) Optimal Tune
It's unlikely you can have one tune providing the same BLMs at 7500 ft and at sea level. If so, drag racers would just use their Houston, TX sea level tune when racing in Denver, CO. and vice-versa. NOT! Can't happen. Many changes are required for preciseness. However for the non-racer, it may be possible to be within an acceptable margin of error. Generally, a very good tune is considered to be 128 BLM +/- 5% (122-132). An acceptable tune is +/- 10% (115-140). Many however believe that BLMs must equal 128 for a good tune. That can only happen in a perfect world.

2) BARO Adjustment while engine running (Normally Aspirated)
ONLY under all of these conditions while the engine is running is a change made to BARO (considered 10 times per second):Now that your eyes are glazed over, you can see this is an extremely rigid set of conditions that have to be met. Not impossible but rare.

If these conditions are met, BARO A/D will be adjusted to equal: MAP A/D counts (always <= 10) from the 0x6CA Table + Current MAP A/D counts from the sensor, from which the BARO kPa is computed as: (A/D Counts x 0.369) + 10.354.

3) Flag 0x018 b4
This is a very important Flag because it significantly affects calculation of BPW and thus BLM:This can be important for tunes at different altitudes because varying air flow is eliminated from BPW calculation. This can provide more consistency as altitudes change and air flow volume changes. But be warned, changing this flag is guaranteed to richen BPW and BLMs significantly based on code simulations:An across the board lowering of VE values will be required.

Also, setting b4=0 comes with advantages and disadvantages. When =0, different ambient temperature-based VE Table values (tunes) might be required to match varying MATs. That could be a problematic where there are significant temperature fluctuations during a day or a season of the year. And, when b4=1, a consistent tune cannot be obtained until both coolant temperature and MAT have stabilized. And with the stock MAT sensor, that may take some time because the sensor will continue to report ever-increasing MAT as the temperature of the heat-soaked plenum continues to rise. Pick your poison understanding the limitations of each b4 setting.

More than enough for now.

 

Sharpe, you're killing me. The files you sent me were not properly updated/changed. I've made the required changes in the attached. Take a look at the XDF Reporting Scalars #26 and #30 below. You did not change the reporting address values and save them to the BIN (Calibration). ADX is OK, but use that attached. You will now have BARO and VE from Table. Also, your VE from Table Conversion was wrong: X * 0.390625X ('X' should not be there)
Have to be detailed with this stuff! Hopefully my changes are right.

Yours


Should be and changed to
Change the title of ALDL Reporting Scalar #26=SC1 INPUT STATUS Bits to "VE from Table" and change the address from "0030" to "01C6".



For future reference, the Packet Number in the ADX points to the ALDL Reporting Scalar to be used to report the item in the ADX (Packet Offset of 26 decimal = Use ALDL Reporting Scalar #26 and report the variable whose address is store there.

Elky

 

Sorry for being a PITA. This is new technology and certainly not natural to me (yet). I am just glad to have the help

I used the three files you sent. I used a prior log session to see how it worked. The Baro VE worked fine and changed as the log played. The VE from Table locked at 95.31 and didn't move, regardless of speed, rpm or Map.

I have to burn it to the chip and will see if the Barometric pressure reads key on.

Attached Pix of dashboard and the Value settings.

 

Barometric Pressure read fine with Key on. I changed the Value to two digits.

 

Not a problem. Just giving you a hard time . But if something is not working, posting PDFs really doesn't help. Need all the files creating the issue + the log.

Can't just rerun a log. Have to create a new one with the new variables. Otherwise, you're just showing the old values with a new title. For example, with VE from Table, you're seeing the new title but EGR % Duty Cycle because your old log recorded values for address 0123 (EGR) instead of Table VE (01C6). Run a new log and you should see correct values. Let me know.

 

Ran a quick log with he car on the stand, a few revs to see some different cells. Looks like Baro VE running about 3.5 points (whatever the measurement is) over the table. Barometer was about .71 which about right for up here in the clouds.

I guess when I am using BLM / 128 for a modification factor, it is taking into account the Baro adjusted VE since that is what the engine is actually seeing for fuel delivery

Attached pix of history table comparisons. and log file

 

The table "VE Adjustment Factor vs Barometric Pressure" seems backwards to me. I would have expected it to read zero at kPa =100 and reduce the fuel as the Barometric Pressure dropped (i.e. higher altitude)

The snip out of the log verifies the multiplier in the 1.11-1.13 range for a barometric pressure of .71 kPa at 7,500 feet asl.

 

See post #2 of this thread. The VE increases as the back pressure on the exhaust decreases.

The intake side of the engine is immune to barometric pressure changes (GM engineers are good!).

RBob.

 

What he said!

Also, looks like your BARO Pressure ADX conversion needs a change. Appears your using X * 0.003906 to arrive at 0.71. It should be: kPa = (X * 0.369) + 10.354. So with BARO A/D at 0xb5 =181 decimal, kPa would be approximately 77.1, which is close to this approximate chart:

 

I will make the corrections. I am struggling with this parameter. As I noted in Post 18, the "VE Adjustment Factor vs Barometric Pressure" table seems backward. In my feeble mind, it made sense that at sea level (kPa =100), the adjustment factor would be zero. But, as you rise in elevation, you need to lean the fuel delivery, of the VE table adjustment factor should be below 1.0. The ECU uses the last Baro and/or the start up Baro to select the Barometric reading. If you are at a higher elevation, to keep BLMs in the 128 range, you need to drop the VE amount in the VE table. Hypothetically, I have my engine in perfect tune at sea level. I drive it up to 7,500 feet and the baro reading drops from 100 to 75. So, the VE Adj Factor vs Baro table would drop the VE setting to a leaner mixture. This would keep BLMs running in the 128 range. I think I realize that the NBO2 will do that for you, but I think the BLM will be off to one end.

It appears my understanding is off base, so I am waiting for the more detailed explanation of how it works.

Second important question. I cannot figure out how to post a chart or image into the body of an email, versus an attachment. It's nice to see it in the body.

Don

 

On the intake/induction side, changes in barometric pressure is automatically taken care of. When at 7500' the most the intake manifold pressure can be is about 77 KPa. The VE table is typically lower here then at 100 KPa. And, since the MAP value is also used in the injector PW calculation, no need to correct the induction side for changes in barometric pressure.

The lower MAP value means a smaller PW.

RBob.

 

This depends upon your email program so there's not one answer. For example, if using Windows Live Mail, must first save pic as a file and then Insert it. Cannot paste.



Am professing up front that I'm neither a meteorologist or physicist, but there are many fueling variables involved at altitude (air volume and density, fuel octane, temperature, humidity, exhaust pressure, etc.). We know all affect engine performance. But as RBob said, the GM engineers were good so must accept what they did as correct.

Looking at your log at 7500 ft, I was curious as to what was the code was actually doing, so simulated the calculation of BARO Adjusted VE. The chart below provides the results. Here's a summary:

• Surprisingly, VE is indeed adjusted upward as altitude increases. The average 12.9% increase at 7500 ft is in line with your logs, so the simulation results can be relied upon. Having looked at this for a while, RBob alluded to what I believe is the situation. At altitude, the VE table will be accessed with a lower MAP than if at sea level. This would mean GM possibly developed the BARO VE adjustment under the assumption that the VE table reflects sea level values. Then when the VE table is accessed at a lower MAP at higher altitude, the sea level VE at the lower MAP is extracted and then factored upward, but by a percentage less than the difference in BARO at altitude and at sea level.
  For example, BARO at 7500 ft is approx 77.1 and at sea level is approx 101.1. That's a 26.4% pressure drop (see chart), which means the VE table at 7500 ft will be accessed with a MAP approx 26.4% below that at sea level. Then as shown in the chart, VE is BARO adjusted upward by approx 13%, approx 13 percentage points, or 50%, less than the BARO percentage difference, thereby leaning AFR from that at sea level. Not sure this is exactly what's happening, but makes sense to justify why VE is being increased at altitude.
  • This would say that if your VE table is tuned to 7500 ft,, you should be running rich, or if BARO Adjusted VE is OK at 7500 ft, you should be lean at sea level. because VE has been reduced due to the 13% VE BARO Adjustment increase.
• BARO adjusted VE at any altitude is adjusted at approximately the same percentage irrespective of the Table value. However, at 100 Table VE, VE is always BARO adjusted to 100 (99.61 in the chart). An exception arises when Table VE approaches 100. Interestingly, as altitude increases, the Table VE value that forces BARO adjusted VE to 100, decreases. This is shown in the last line of data at each altitude.

Hope this makes sense.

Elky

 

You need to change you title line from "If it was easy --- everybody would be doing it!" to "if it was easy to understand, everyone wouldn't ask questions"

I realize I am conversing with the two Gurus of Tuning here, but bear with me:

Here's my understand of RBob's response (which makes sense to me).

If you are at sea level when you tune your VE tables, the 100 kPa Map amount will be greater (for each RPM row) than the 75 kPa amount. So, when you drive from Sea level to 7,500 feet, the WOT amount moves from the VE amounts in the 100 kPa column to the 75 kPa column and the A/F mixture is leaned accordingly. That makes the assumption that when you tuned the VE tables, you were reasonably accurate in the de-escalation of the VE values in the table for declining. kPa.

This also makes the assumption that you have no other factors weighing in on the calculation (such as the "VE Adjustment Factor vs Barometric Pressure) table

From Elky's analysis, the VE Tables are computed at Sea Level. So, WOT is 100 Kpa at sea level and the VE in the table at 77 kPa (at sea level) is based on a sea level fuel adjustment (air density) WOT at 7,500 feet is 77 kPa. However, according to the GM engineers, the 77 kpa VE amount (in a sea level computed table) is not equal to WOT required VE at 7.500 feet. The amount is lean by 12% (plus or minus). So GE-E added the 12% (or table amount0

So, 77 kPa (at sea level) table VE is equal to WOT (at 7,500 feet asl) table VE value times the adjustment factor in the "VE Adjustment Factor vs Barometric Pressure" table

Getting personal here.

I am adjusting VE table at 7,500 feet. kPa 77.

1, Assume the VE table value at 1400 rpm at 50 kPa is 53.91.
2, The VE Adjustment factor vs Barometric pressure is 1.14
3. Because of that factor, the engine fueling is seeing a VE amount of 61.46 (53.91 x 1.14)
4.. Assuming the GE Tables are accurate, when I drive the car at sea level, the VE at 1400/50kPa will be back to the 53.91

 

*deleted*
I need to read up more on this stuff.

 

The ECM needs to get a current Barometric reading from somewhere, in this case the MAP sensor;

Bingo. And based on that reading the ECM will look at the Barometric curve for a correction value;

Bingo. You then tune the Barometric Correction table based on what the engine is asking for through your own observation of the varying air/fuel ratio being reported during exhaust backpressure related circumstances, not on the intake side...

Bingo.

Quote:

Originally Posted by Sharp38

I have noticed several instances when doing test runs where after the first run, for example, I am lean BLM History Table. I use the BLM/128 method of arriving at proposed changes to the VE table. I make those changes. The next run a day or so later, I am now on the rich side. I originally was using manual and automatic "smoothing" and attributed the "overshoot" on the VE adjustment to the smoothing process. The last few times, I have abandoned smoothing (at least for the time being) only correcting a few obvious dips or peaks (in the graph)...

This has nothing to do with Barometric Correction.

Upload an image of your VE table and you will see why the above is happening...

- Rob

 

Replying to your post #24 because too much to quote, Two things:

1. You're quoting your VE numbers that we can't see, so hard to respond. Best to post files also so reference can be made to your comments.
2. But let's back up for a moment. Here's the bottom line of what you're going to see with VE:
   At 7500 ft: BARO Adjusted VE = Table VE + 12.5%-13.3%
   At S/L: BARO Adjusted VE = Table VE + 1.6%

Just need to see what AFR or BLMs you get at S/L. Might be OK at S/L because you will be extracting VE from the table at higher MAPs (ie - VE should be larger at higher MAP). It's a dance that continues. Never perfect.

 

Good one!

 

Your cars use a MAF sensor that directly measures air mass going into engine. Why would you need any baro compensation with a setup like that? Is it because of unmetered flow from EGR going back into manifold?

 

He is running $8D which is Speed Density based... the earlier MAF cars needed positive and negative Baro correction, but MAP, as well as MAP & MAF used in conjunction that followed, not so much. GM used other parameters in the latter's code to compensate for any change in the air density, though Baro correction was still apart of the code. RBob stressed the exhaust side with Speed Density because Baro would be used to compensate for the areas not directly measured by the the MAP sensor, mainly exhaust backpressure triggered...

- Rob