Spark vs altitude BP
Definition:Base Spark Table high altitude
Platform:All
Min Value:
Max Value:
Description:
The x coordinate is the barometric pressure in inches of mercury, the y-coordinate is the amount of
ignition advance that is added (or subtracted if the number is negative) to the overall ignition
advance.
Hints:
A higher number increases ignition advance and a lower number decreases ignition advance.
Spark vs sealevel BP and Spark vs altitude BP are used
based on barometric pressure. Barometric pressure above 26in/hg and the EEC will use the Spark
vs sealevel BP while a barometric pressure below 26in/hg will use the Spark vs altitude BP. To
configure spark set all 3 spark tables (sealevel, altitude, & ACT) to the same values. The spark
tables are read in column’s top to bottom.
Example: Assuming that you are using the stock X any Y normalizers, while waiting at the tree
(drag racing) the vehicle is idling at 900 rpm. This puts the spark in column 0 (500rpm’s),
at green, the engine accelerates to WOT. Before the rpm’s reach the next defined level in the
Spark Table X normalizer, which is column 6 (2000rpm’s) the spark does not change. This is
based on a 140% load from idle column 0 to column 6. Even though the table has 9 rows for
spark it only reads what is defined in the X normalizer. In this case it is 2000rpm’s where
the EEC will set the timing at 12 degrees and then column 8 (3000rpm’s) where will set timing
at 20 degrees and so on.
Taken from a discussion, Ill try to clean it up later:
Currently only the A9L.dat file has the correct labeling, but this
applies to all in the title (probably all pre-94 MAF EEC-IV units).
This does not apply to 94+ EEC's, where you should read David's
message from a while back regarding "borderline spark." I will update
the other A9* dat's shortly.
First lets look at how altitude vs. sea-level is determined...
The functions involved for spark are:
spark_vs_BP_altitude
spark_vs_BP_sea_level
(Use fixed width font) _______
1 | ______ _________/
| \ /
| \ /
| \ /
.5| Sea X Altitude
| Level / \
| / \
| / \
|--------------------------------
31 27.75 26.5 12 (BAP)
Notice how the two functions when overlapped clearly show where
sealevel vs altitude spark tables are used. Notice how there is a
smooth transition from one table to the other. These functions
probably don't need to be adjusted, but are useful to see how it
works. However if you live in an area where barometric pressure is
often in the 26-28 range, perhaps a little skewing for predictability
would be good.
So...
Part Throttle Spark =
(spark_vs_BP_altitude * spark_table_altitude) +
(spark_vs_BP_sea_level * spark_table_sea_level)
Scenes from our next episode... "Lugging" (high-load, low RPM)
spark.
Other observations:
Really low atmospheric pressures yield a spark multiplier of up to
1.2. Anyone live where BAP is lower than 23?
- I believe the EGR tables use the same principle. However, there is
a separate EGR multiplier for altitude called "EGR_alt_vs_BP." Note
that at really high altitudes (low BAP), the EGR is effectively
disabled.
Alex
PS: Derek - You probably don't want to adjust the load-limits. If
you do want to use them, you will need to enable those functions with
the corresponding scalar. I believe these adjust the load
calculation to be based on those functions instead of theoretical
volumetric efficiency. In other words, most mild N/A engines will
not ever see 90% or higher load, assuming the MAF curve is accurate.
These functions allow you to use the full effective range of the load
based tables in this situation. I still need to look further into
these.
**********************************************************************************
Alex,
1) If the tables overlap, how does the EEC know which to use? I see
no need to overlap. They do need to share a boundary and continuity
at the boundary, or switch point, would make sense. The only point
that meets these criteria is (27.75+26.5)/2.
2) I interpreted the open_loop_load_limit_vs_ECT differently. Eric
Goehl wrote in the datalogging section of his site, "High load
is defined as a load (VE) greater then 70% when warm, or 80% when
cold. Presumably setup like this because when cold, the car is
running richer then normal anyway, so HLoad enrichment can be delayed
a bit." This is the relationship I was referring to.
Derek
*************************************************************************************
1) The eec is technically always using both altitude and sea level
timing tables at the same time during part throttle. Yes, the
overlap boundaries do need to make sense. Essentially you want the
barometric pressure functions to be the inverse of one another and
their addition at any BP value (above a certain point = 23?) to equal
one. So in the A9L example above 27.75, only the sea level actually
affects the timing. Below 26.5, only the altitude table gets
applied. In between, the result is an interpolation between the two.
2) You may be correct. I wish I had datalogging capabilities to
verify some of these things. Like I said in the previous message - I
have more checking to do...
Alex
****************************************************************************************
Alex just didn't list the tables, or it would make sense. The 94+ just uses
one multiplier, and uses:
BP_multilier * base_spark + (1 - bp_multiplier) * alt_spark.
Here you can clearly see the relationship, and the bp_multiplier is used to
move the interpolation point closer to one or the other tables.
David
P.S. I didn't use the real names here
A9L Spark Discussion
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