LT1_Edit Users guide
The OBD-I editor only works with 94 and 95 PCM images from the 16188051 & 16181333 . This
covers all GM LT1 & L99 Applications for the 1994 and 1995 Model years.
Use this Editor at your own risk. Incorrectly changing Variables in the PCM can damage the
Engine and the Transmission.
The OBD-I editor is available in two versions: Standard and Expert. These screens are from the
Expert version. There are no Fuel or Ignition pages in the Basic editor. It is basically a
replacement for an HPP programmer. It allows you to control the Transmission shift
characteristics, and the Coolant Fan Temperatures. The text will indicate when a feature is not
included in the Standard version.
The opening screen should look like this:
Opening a File:
When starting the editor, go to the “File” menu and select “Open”. The editor assumes you have a
*.LT1 file for your PCM. This file contains the Flash images from both PCM processors. Both
PCMprog & OBD2prog read and write the flash using this format. Before you start editing a file
make sure you have backed up an original copy of your *.LT1 file. If your new changes to the file,
don’t work well in your car, you always want to have the original file for a safety backup.
Editing a file:
When LT1_Edit opens a file it will determine the file type. It should say “94-5 LT1 file” in the
Prom Type window. These are the only file types that LT1_Edit currently supports. After loading
a *.lt1 file “edit “ on the menu bar should now be enabled.
Notepad
Note pad is a 256 character scratch pad. Whatever you write on this notepad will be save in the
Flash binary. Use it for your tuning notes, and it will always be with the chip.
Function Enable
The Expert Editor includes this function menu, it is not in the Standard version of the editor. It
allows you to toggle the following PCM functions On or Off.
Traction Control
Speed Density Mode
This is necessary if you remove the MAF – It is mostly for Street Rodders, and
Engine transplants. Not recommended for most applications.
Crank A.I.R.
Disables the Air Pump
Vehicle Anti-Theft
This disables the GM VAT system that uses the Key pellet. This should only be
disabled with engine transplants to vehicles that don’t have the key pellet reader.
Transient Fuel
This disables the Charcoal Cannister air purge.
The EDIT Menu contains the following selections. Each will be discussed in a separate section
after the How to edit Section:
Engine
Fuel
Ignition
M6 Transmission
A4 Transmission
Checksum
Gear/Tire
Chassis
How to edit tables
Once you have selected an area to edit, you will see a window with three tabs at the top of the
window: Table Edit, Graph View, and Select Rows.
Table Edit
If you point to any cell in the table and click the left mouse button, the selected
cell will have a gray background, and the cell content will be displayed in the text
window in the upper left of the display window. This display works like the old
excel spreadsheet format.
All changes must be made in this single text window on the upper left of the Table edit display. To
transfer this new data to the highlighted cell, just point the mouse to a new cell and click the left
mouse button. All changed cells will show a blue background. You can edit any number of cells.
Since the change takes place when you leave the cell, make sure you leave the last cell you made
changes in, by clicking on a new cell.
If you don’t like your changes click the “clear changes” button to go back to the original data.
When you are satisfied with the new table you can commit it by clicking on the “Apply Changes”
button.
NOTE: When you enter a value and move to the next cell, you may find that the saved value has
changed from what you originally entered. The editor allows you to enter a value in scaled units.
When the data is saved, it must be quantized into the nearest single byte or integer value. The
value shown after saving is the closest value in the PCM’s internal format to the number you
entered.
Copy & Paste
This release introduces a new way to edit tables. The table edit screens now have File and Edit
menus in the Upper left corner. When you select Copy, All the Highlighted cells are copied into
memory. When you paste, that copy is copied into the highlighted cells in the table you are pasting
too.
You can cut and paste a block of one table. into another table. I do not check to make sure the cut
and paste blocks are the same size, or that the Table types match. You must make sure they are the
same size and type. .
This is for requested features like copying the High Octane table to the Low Octane table. You
can also cut and paste from one file to another. But you cannot exit the editor between files. This
can be used to cut and paste a table between two different GM Builds. It is up to you to make sure
the axis match.
To copy a table between two different GM Builds try the following:
Open file A
select a table
from menu select Edit > Select_all
from Menu select Edit > copy
go back to main screen
use File > OPen to open File B
go to the same table
from menu select Edit > Select All
from menu select Edit > Paste
hit apply
You should now have the table from A in the File B
Edit Whole Table Frame
You can edit all cells that are visible on the graph at once. The Frame “Edit Whole Table” will
apply these changes to all the Visible graphs. You have 3 choices in this Frame:
1.
Add a value. The value you enter in the value window is added to all cells. Note a
negative number in the cell will subtract the value from all cells.
2.
Fill value. All cells will be set to the value in the Window.
3.
Multiply by %. Entering 100 will result in no change. Enter 50 and all cells will be cut
in half. Enter 150 and all cells will be 1.5 times the current value.
There is one other option in the Edit whole table Frame. If the “Use selected cells only” checkbox
is selected, all changes apply only to the highlighted items. The Highlighted items can be selected
by pointing to a cell, holding down the left mouse button, and dragging across an area. Any
rectangular area in the table can be selected, but random single cells cannot be selected.
Compare File Frame
You can open a second file and compare or copy tables from it. In order to use these features, you
must use the Read File button in the Compare file frame to read in the second file. This second
file must be from the same GM Build. Version 1.2 adds a test for this compatibility. The file name
of the second file will now appear on the second radio button
If you select the top radio button, you will be viewing the data in the original file.
If you select the second radio button, you will be viewing the data in the compare file.
If you select the third radio button – Difference you will be looking at the difference in the two
files, on a cell by cell basis.
While viewing the original file, if you click on the Copy File button, it will copy the data in the
visible, part of this table from the compare file to the original file. The Use Selected cells option
also works for this feature.
Graph View
Graph View presents the information available in the Table Edit in a graph form. Information is
not editable in this view. To change variables, you must return to Table Edit view. However, you
may change the appearance of the graph by choosing either a
2- or 3-dimensional graph display using the radio buttons at the bottom of the Tab.
Transmission Calibration Graph View
Note: If you hold down the CTRL key after selecting only the 3D Graph radio button at the
bottom of the graph, you can change the angle and viewpoint by rotating the graph with your
mouse.
Select Rows
The selected rows tab simply displays the rows that appear in the Table Edit view. Compare
Figure 7 below with Figure 5 as an example of the relationship of the Selected Rows view with the
Table Edit view. If you uncheck a row, it will no longer be included in the displayed Table, or
graph, and will not be edited in the edit whole table Frame. The data will remain in the file, but be
unchanged.
Transmission Calibration Selected Rows
Engine
This page presents The Idle control tables, and access to the emissions parameters.
Idle Speed
This function presents an editable idle table of idle speed vs. temp. There are two
separate graphs. One is idle speed while in gear, the second is idle speed while in Neutral
or Park.
Idle Air Control
Allows you to set the Default IAC counts as a function of Coolant
Temperature.
IAC Throttle Follower vs MPH
The Throttle follower controls the return to idle when you back off the throttle
Idle Spark
Cylinder Balance
Test Parameters Tab
EGR Control Parameters
Catalytic Converter Overtemp Parameters
Fuel
This function is in the expert version only, it opens a new page dedicated to editing fuel
delivery.
Open Loop AFR vs. Load vs. Temp
This table sets the target Air Fuel Ratio when in open loop
%TPS for WOT vs. RPM
This table defines hwen the PCM goes into WOT fuel mode
Power enrichment vs. Temp
This table defines the % change in Power enrichment used in WOT
mode.
Power Enrichment vs. RPM
This table defines the % change in Power enrichment used in WOT
mode.
Volumetric Efficiency 0 to 7000 RPM vs. %TPS
This table is used only in open loop. The Car cranks in Open loop, and
transitions to closed loop after startup. This table will effect the
transient behavior, as the car moves from Open to closed loop.
MAF Calibration Frequency vs. Air Flow
This table is used to calibrate the MAF.
Cylinder size
Injector size
Injector Offset vs. Voltage
This table defines the Fuel injector dynamics. Think of this value as
the time it takes for the injector to open, after you send it the voltage
listed.
Closed Loop Enable
There are three parameters her. The MAT Threshold is a Manifold
temperature. Below MAT is the coolant temp required to go into closed
loop when below that temp, Above is the Coolant Temp required to
start closed loop when above the MAT threshold.
BLM Control
BLM = Block Learn Multiplier. It is the way the PCM learns about
small changes. A block learn of 128 means that the fuel control is
perfect. If the BLM is below 128, then the PCM believes the engine is
lean, and will add fuel. A BLM above 128 means that the PCM thinks
the engine is Rich, and will subtract fuel in closed loop. These
parameters control the Block Learn algoritm, and define the 16 basic
Block learn Cells.
Decel Fuel Cutoff
These parameters control the fuel cutoff under coast down.
Ignition
This function is only in the expert Version, it presents a new page dedicated to editing the Ignition
timing tables. The Ignition Table format only allows positive numbers. The Offset can be used
with the tables to shift the table so it may contain negative numbers . The Values viewed in the
Table edit already include the offset value. If you add 2 to the offset, It would add 2 to every value
in the table.
Load vs. Advance vs. RPM
This table is Spark advance as a function of MAP and RPM
Load vs. Temp vs. Advance
This table is a correction to Spark Advance as a function of MAP and
Temperature. There is a separate table used during Cranking.
Closed Throttle Spark Advance
This table is used under closed throttle conditions
Minimum Spark Advance
Minimum Spark Adavance as a function of RPM
Knock Retard Attack Rate vs RPM
This is a measure of the knock retard added for each knock event that
occurs
Knock Retard Decay vs RPM
This is the amount of Knock retard removed for every couple of engine
revolutions.
Burst knock Parameters
Burst Knock is a retard that is created by the PCM when it detects a
heavy load at Tip-in
Maximum Knock Retard vs. RPM
Maximum Knock Retard vs. MAP
Maximum Spark Advance
Maximum Retard
Torque Management
M6 Transmission
The M6 Transmission menu lets you change all the CAGS (Skip Shift)
parameters.
A4 Transmission
Shift Speed
Note: Most models default to performance mode, the Firebird lets you switch
modes. The Basic edito does not include the Hot and Cold shift parameters.
Normal Mode Shift Points - Gear vs %TPS in MPH
With the transmission in Normal mode, this table allows you to set the shift
MPH vs %TPS (% of Throttle position) for each gear upshift, and downshift
Performance Mode Shift Points in MPH
With the transmission in Performance mode, this table allows you to set the shift
MPH vs %TPS (% of Throttle position) for each gear upshift, and downshift
Manual Mode Shift Points in MPH
This table applies when you have the transmission lever set in the lower gears
and try to Manually shift the A4, this table allows you to set the shift MPH vs
%TPS (% of Throttle position) for each gear upshift, and downshift
Shift Pressure vs. Temperature vs. %TPS
This table allows you to alter the line pressure in the A4 transmission. Lower
current values in this table result in Higher transmission pressures. The higher
pressures cause firmer shifts. You usually only modify the curves for normal
operating temperatures.
Line Pressure vs %TPS vs MPH
This table modulates the shift firmness
WOT (Wide Open Throttle) upshift and Downshift in MPH
These values only apply at Wide Open Throttle
Hot up and downshift in MPH
Normal, Hot, and Cold shift vs. RPM
PRNDL = Low
These are the Are the 1-2 and 2-1 Shift MPH values when the shift lever is in
the Low Position.
Shift Firmness
Shift Pressure vs. Temperature
This table allows you to vary the shift firmness as a function of Temperature and
throttle Position
Line pressure vs. % Throttle Position
This table allows you to vary the shift firmness as a function of MPH and throttle
Position. Not in the Basic editor.
Normal Mode Pressure Offset vs. %TPS
This Offset Table will vary the shift firmness By gear as a function of Throttle
Position, When in Normal Mode
Performance Mode Pressure Offset vs %TPS
This Offset Table will vary the shift firmness By gear as a function of Throttle
Position, When in Performance Mode
Target Shift Time in Seconds
This is a target time for the shift to complete. DOD NOT ZERO IT, that can damage
the transmission
Maximum Line Pressure
This Is a limit imposed on calculations in the PCM.
Torque Converter Clutch
TCC Apply vs. %TPS vs. MPH
This sets the Speed at which the Clutch is applied for each gear and Mode.
Not in the Basic editor.
TCC Release vs. %TPS vs. MPH
This sets the Speed at which the Clutch is released for each gear and Mode.
Not in the Basic editor.
TCC Apply MPH
These are the values used at WOT
TCC Release MPH
These are the values used at WOT
TCC Shift Delay
This is a target shift time for the PCM. It should not be set to 0. The
transmission does need time to shift. Not in the Basic editor.
Misfire Counts to disable TCC
Checksum
This function will calculate a new file checksum based on the GM algorithm and tell you
if the onchip checksum is still correct. It is not really needed. Many people would forget
to fix the checksum, so I automated the checksum correction, and it is automatically
applied every time you save a file.
Gear/Tire
This routine is used to scale the 4 scaling bytes, and all of the MPH based shift tables for
changes in the tire size and rear end ratio. This results in changing over 600 Bytes.
Because of quantization errors that are introduced in multiple rescales, you should always
start gear rescaling with an original GM calibration that has not previously been rescaled.
The scaling Algorithm is based on the Body and transmission type, so the first
screen is to verify the body and transmission.. If the automatically determined Body or
transmission type is wrong , then use the radio buttons to correct the data.. I have not seen
any stock file that was misidentified.. SO use caution if you change it.
For Gear/ tire. I initialize the screen to the default tire size, and use that to
calculate the gear ratio. If your tire size is different, enter the correct Tire diameter. It will
recalculate the gear ratio in the Flash. If you don’t know the tire Diameter in inches, then
select Tire size and enter the tire size as the width, ratio and rim diameter.
To change the Gear ratio, You enter the new gear ratio in the Change Gear Ratio
Frame. Under most conditions you should leave the Both button checked. Some tuners
scale the Speedometer and the internal transmission scales differently. This is a trick used
with 4.10 and higher gears. I don’t recommend it for 3.73 or numerically lower gears.
Clear will set the values back to the original values, If you press it before you
use the Apply button. You must use the Apply Gear scaling button to put the new values
in the Flash image, and scale all of the MPH tables. Once you use the Apply Gear Scale
Button the Flash image is updated and clear takes you back to this new image, not the
original values.
Chassis
This function will allow you to change:
Fan On Coolant Temp
Low speed temperature when below MPH threshold
High speed temperature when below MPH threshold
Low speed temperature when above MPH threshold
High speed temperature when above MPH threshold
Fan Off Hysteresis
MPH threshold speed
Fan On Oil Temp (only used on Corvette A4)
Low speed temperature when below RPM threshold
High speed temperature when below RPM threshold
Low speed temperature when above RPM threshold
High speed temperature when above RPM threshold
Fan Off Hysteresis
RPM threshold
Speed limit fuel cutoff
RPM limit fuel cutoff
In the Fan On Temperature Frame there are seven variables. The fans work differently in
different body styles.
For the F-Body, The first stage has both fans running at low speed. The second stage is
when both Fans are turned on at Full speed.
For the B-Body, The first stage is when one fan is turned on, the second stage is when
both Fans are turned on at Full speed.
The Corvette has an Oil Temperature based Fan control too. It is not used in the B or F
bodies.
Under each stage there are two settings, the PCM uses the first setting when the car speed
in MPH is below the Fan Speed threshold, the second setting is used when the car road
speed is over the Fan Speed threshold.
The Hysteresis is the temperature drop required before the fans turn off. The upper
Hysteresis value is used when the road speed is below threshold, and the lower value is
used when the road speed is above the threshold.