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Programming PROMs for your Thirdgen Fuel Injected F-Body: Part I Introduction

By Tim Siford, aka Traxion ( trax@frederickmd.com )

Warning: The information presented below is presented for educational purposes only. Use this information at your own risk. Be aware of your emissions laws and be aware that changes to the car's stock computer chip can cause your car to no longer be compliant with State and Federal emissions guidelines. Furthermore, be aware that changes to a car's stock computer chip can have very serious detrimental consequences to both your car and those individuals in the car as well as innocent bystanders outside the car.

OK, with that said, let's get right to it. You want to program your own chips right? Maybe you're sick of paying ridiculous prices for a 'custom' computer chip. Maybe you're sick of having to depend on someone else to get your calibration right. Or, maybe you're just determined to do it yourself. Well, you've come to the right place. Many sites on the Internet go directly into what a PROM is and give you all sorts of technical information that can be very useful once you understand the basics. But, the fledgling thirdgen PROM programmer isn't really concerned with this information. Most of us performance oriented '85-'92 F-Body aficionados already know that there is a computer chip in our car that has certain calibrations for spark, fuel, etc. What we really want to know about custom programming chips is...

What will I need?
How do I do it?
And... How difficult is it?

What you need...

  1. You need a computer. No big deal there because if you are reading this then you have a computer.
  1. You need a piece of equipment that can read and program PROMs. This is most often called a 'Programmer'. This piece of equipment will be utilized to read and program your PROMs. The Programmer connects to your computer through the computer's communication port (COM or Parallel port). When you buy the Programmer it will come with software that communicates with the Programmer. This software is installed on the computer to which the Programmer is attached and it is used to control the Programmer (for reading from and writing to the PROM). Reading PROMs will produce an image of your PROM stored in a file with a .BIN extension (binary). It is this binary file that must be modified in order to change things such as fuel and spark parameters. The binary file is often called a BIN. I use a Programmer called the 'Pocket Programmer' that is made by a company called Xtronics. It is reliable, easy to use, and economically priced. It is also an external unit (you don't have to install it inside your computer). This means that I can take it with me if I need to custom program a chip away from home (like at the local dragstrip!).

    Pocket Programmer
    Source: Xtronics
    PN: I-PP2
    Price: $150.00

    Be aware that there are many other types of Programmers on the market. Two of the more popular Programmers can be found at the following Internet sites...

  2. You will need ANOTHER special program to read this BIN and allow you to modify it. This 'other' program (also known by the word 'Editor') is not supplied by the company that makes the Programmer. It is not supplied with your Programmer. I use an editor called 'TunerCat'. TunerCat is available at http://www.tunercat.com. However, there are several other programs available on the Internet that you can use. A couple of the most popular ones are:

    1. WinBin (Windows Based) - http://www.passtimeracing.com/eric/Cars/EFI/index.htm
    2. GMEPRO (DOS based) - terryk@foothill.net

    ALL of these editors have special calibration files (also known as definition files) that you load into the program before opening your BIN. This calibration file tells the editor exactly how to read your BIN. The BIN needs to be interpreted appropriately and the 'calibration' file takes care of this. This is extremely important because not all EPROM images are organized in the same manner. A good example of this would be comparing a 1989 IROC-Z to a 1990 IROC-Z. The 1989 IROC-Z uses a Mass AirFlow Sensor (MAF) in order to directly measure the amount of air entering the engine in order to supply the appropriate amount of fuel. However, a 1990 IROC-Z, which uses Speed Density engine management, does not have a MAF and does not directly measure the amount of air entering the engine. Thus, you would expect that these cars would have different code in their EPROMs. Well, in fact, they do. Thus, the editor needs to know where to find the appropriate information inside of the BIN. This is accomplished by loading the calibration file into the editor before loading the BIN. In reality, each ECM (Electronic Control Module) has a specific type of EPROM and a specific organization of the code contained in that EPROM. EPROM type and EPROM organization can change from one year to the next so it is important to know what type of EPROM you have in your car and the common term for the EPROM organization (also known as the 'Mask'). See the table at the end of this tech article to view the information for your F-Body.

  3. Spare EPROMs. It's much easier to just pull your existing chip out of the ECM and then slap in the new one with the updated calibration instead of constantly reprogramming the same one. The only way to do this is to have spare EPROMs. You can order EPROMs from various sources on the Internet. But, you need to be aware of the specific EPROM type that your F-Body's ECM needs. As noted in Item 3 above, the EPROM type is specific to the year of your F-Body and engine type (TPI, TBI, etc.). When shopping for EPROMs you will notice that they are available in many different speeds very much like memory for your home PC. Most custom programmers have noted that you can use any speed of chip available. This is great because the slower EPROMs (250ns) are cheaper than the faster EPROMs (50ns) and they work just as well. Moreover, some EPROMs are labeled as OTP EPROMs. OTP stands for One Time Programmable. Do not buy these PROMs because they can not erased.

    There are various sources for EPROMs. I have noted a few below...

    EXAMPLE: 1990-1992 TPI F-Bodies (305 and 350) require a '27C256' EPROM. See the table presented at the end of this tech article to determine the type of EPROM needed for your car. For EPROMs, I am using the following for my 1990 IROC 350:

    28-pin, 256K CMOS EPROM (32K x 8), 90ns, CERDIP
    Source: JDR Microdevices
    PN: 27C256-90
    Price: $3.99 http://www.jdr.com/interact/default.asp

  4. If you are using EPROMs (and not EEPROMs - see the important note below) you will need an EPROM eraser . You need to erase the EPROM before you program it. Exposing EPROMs to UV light erases them. Thus, an EPROM eraser is a piece of equipment that has a UV light bulb (that shines at a particular wavelength) and a place to put the EPROMs so that they are exposed to the UV light in the device. Every EPROM (except OTPs, One-Time Programmables) will have a small quartz window on its top surface. This quartz window gives visual access to the true hardware that stores the information (basically 0's and 1's). On stock GM EPROMs this quartz window is covered with a small silver sticker that has the GM part number on it. Removing this small sticker will reveal the quartz window that yields visual access to the memory module. This small sticker prevents UV light from entering the EPROM. This is important because you do not want sunlight to begin to erase the EPROM. Now, in theory, it takes a couple of weeks in the sun to erase the entire EPROM. However, several custom programmers have noted that their EPROMs were fully erased in only 2 days in direct sunlight! So, be careful. Always cover the quartz window before programming your EPROM. If you don't have a sticker to cover the EPROM window or if your GM sticker loses its stickiness then use electrical tape. Electrical tape can withstand the heat that the EPROM will most likely experience. Regarding EPROM erasers I use a DataRase II which is very common among EPROM programmers. Never look at the UV light bulb or expose your skin to it! It is dangerous to your eyes and skin. It could cause permanent damage!

    DataRase II EPROM eraser
    Source: DigiKey
    PN: ER2-ND
    Price: $39.95

    IMPORTANT NOTE: The 'rage' among us chip programmers is the use of flash proms (called EEPROMs for Electronically Eraseable Programmable Read Only Memory). EEPROMs make our lives much easier in that a UV Eraser becomes obsolete. To program an EEPROM you simply put the chip in the programmer and program it. The programmer will both erase the chip and reprogram it. This is wonderful. There is no need for a UV Eraser, no need to wait for chips to erase, and the chips have a much longer burning life since they aren't being pounded by UV light! The magic part number here is AT29C256. It is a 32Kb chip manufactured by Atmel. This chip is a direct replacement for all 27C256 chips used in 1990-1992 TPI F-Bodies (32Kb). This does NOT mean that it cannot be used in previous year TPI vehicles. You just need to do a little 'tweaking' during the programming process. 1986-1989 TPI F-Bodies use a 27C128 chip of 16Kb. The Atmel AT29C256 chip has twice as much memory. To make these chips work on 1986-1989 TPI F-Bodies you can do one of two things: either make sure you program the BIN into the last 16Kb of the 32Kb EEPROM (using options on your programmer) or just double the BIN using DOS commands and then program the EEPROM. For the DOS method just take the BIN you wish to program and name it test1.bin. Copy it. Rename the copy test2.bin. Finally, go to a DOS prompt and type "copy /b test1.bin+test2.bin test.bin" (without the quotes). You now have a doubled BIN called test.bin that you can program the AT29C256.

    That's it! That's all you need. You can purchase reliable equipment for items 2-5 for around $200 (not including the Editor). Yes, you heard correct. For $200 you can be burning your chips! When using EEPROMs the cost is substantially less than $200! But, it will take a lot of background information, a lot of testing and experimenting, and a lot of experience before you become talented at doing it.

How you do it...
  1. Hook up your newly acquired Programmer to your computer as per the Programmer's instructions.
  2. Load the Programmer's software, Run the software, and choose the correct EPROM type.
  3. * Pull your computer chip from your car and put it in the Programmer in the correct manner.
  4. Use the Programmer's software to read your chip.
  5. Save the chip image to your hard drive. This is the BIN.
  6. Remove your computer chip from the Programmer and shutdown the Programmer's software.
  7. Run your Editor.
  8. Load the correct calibration file.
  9. Load your BIN.
  10. ** View/Change the chip's parameters and tables.
  11. Save the new BIN.
  12. Shutdown the Editor and run the Programmer's software.
  13. Ensure the correct EPROM type is selected.
  14. Place an erased chip on the Programmer.
  15. Do a 'blank check' to ensure the EPROM is erased.
  16. Program the EPROM with the BIN saved in step 11 and then verify the program.
Simply put, that is how you program EPROMs for 1985-1992 F-Bodies. Steps 1-9 and 11-16 are the easy steps.

Step 3 marked with '*' may require more work on your part because the EPROM in all TPI equipped 1986-1992 F-Bodies is physically attached to a carrier. This carrier is a bigger plug-in module that inserts into your ECM. Most inexperienced F-Body enthusiasts mistakenly call this the 'chip'. However, for '86-'92 TPI F-Bodies it is more than a 'chip'. Technically speaking, this carrier is called a MemCal. MemCals are easily recognized by their bright blue protective cover. Underneath the blue cover, the MemCal will contain the bare EPROM along with the limp home mode chips (netres, short for network resistors) and possibly the ESC Filter ('90-'92 TPI F-Bodies, aka Knock Module). Thus, it is not as simple as pulling the chip out of your car and putting it directly into the Programmer if you have a '86-'92 TPI F-Body. If you have a TBI equipped F-Body then you do not need to worry about this because the EPROM plugs directly into the ECM; there is no MemCal. For you '86-'92 TPI owners, there are 3 ways around this. Each method is mentioned below along with pictures. A more detailed explanation of each method follows.

  1. Desolder the EPROM from the carrier and then solder a Zero Insertion Force (ZIF) Socket in its place so that you can take the chip on and off at will. Here are some pictures that document this method:
  1. Stock GM MemCal
    Stock GM MemCal with protective cover removed.
    Low-Profile ZIF
    Modified GM MemCal with ZIF
    Modified GM MemCal with ZIF and new EPROM

  2. Make an adapter to burn the PROM while it is still in the MemCal. This is the method similar to what the big chip people use (i.e. TPIS, AS&M, etc). Here are some pictures that document this method:

    Adapter in its modified and original form
    Adapter in the Pocket Programmer #1
    Adapter in the Pocket Programmer #2
    MemCal attached to Adapter in Pocket Programmer

  3. Method 3 is the most popular method and is, in this author's opinion, the best way. Obtain a used HyperTech, ADS, or Jet 'chip' adapter or purchase the adapter from Craig Moates (please see Craig's MemCal adapter page for more information). This makes things very easy because it comes with a chip socket that is already heavily soldered to a thick computer board. With the HyperTech, ADS, or JET adapters you just pry out the existing EPROM and put in your own. Your existing MemCal piggybacks onto the adapter so that the limp home chips and ESC Filter ('90+ TPI) are still used. Easy. Here are some pictures that document this method...

    MemCal Adapter
    MemCal Adapter with EPROM
    MemCal Adapter with EPROM and MemCal

    Craig Moates' adapter is very nice because it comes with a ZIF and, therefore, makes the chip exchange very easy with the absolute least wear and tear on the ECM's or MemCal's socket. Please keep in mind that everytime you remove the MemCal or the adapter from the ECM you are putting wear and tear on the socket! Using a Craig Moates' adapter or something similar will prevent this because you can simply leave the adapter in the ECM and use the advantages of a ZIF by just removing the chip from the ZIF. Now, if you do manage to find a used HyperTech, Jet or ADS adapter really cheap don't pass up on it! I have successfully installed the low-profile ZIF mentioned in step 1 into one of these adapters by simply pressing it into the open socket and using some hot glue to secure it for peace of mind. This is what I have been using and it works like a charm. Please note that if you utilize method 3 then you will not be able to reattach the cover plate for the ECM. This, however, is not a big deal. Once you get the BIN worked out simply follow method 2, install the MemCal and cover plate, and put the ECM back into the dash. Some people even purchase an extra AT29C256 and solder it into the actual MemCal in place of the stock 27C256 or 27C128 to make using method 2 that much easier.

Option #1 Explained: When using option 1 I used the following parts to construct the ZIF MemCal...

Socket 28PIN ZIF Lo Profile
Source: Digi-Key
PN: A347-ND
Price: $6.50

Soldering Iron Tip .015 Conical
Source: Digi-Key
PN: K342-ND
Price: $7.95

Soldering off the existing EPROM can be tricky. But, it is not that difficult. You will want to make sure that you utilize a solder iron with a very fine tip (which is why I have listed a part number and description for one above). Big and/or thick tips will not work. You will want to gently pry up on the EPROM with a jeweler's screwdriver as you desolder the legs one at a time. It is a slow and crude process, but it works beautifully. Be patient. Some individuals have found that using a 'solder wick' helps ease this process. A solder wick sucks up liquid solder so that you can remove it easily. In any case, once the EPROM has been removed from the MemCal simply solder in the ZIF socket. CHECK FOR CONTINUITY using a Digital Voltmeter (DVM). This is of utmost importance. You want to make sure that each pin on your ZIF really is connected! Finally, use a hot glue gun to firmly attach the ZIF to the carrier. The solder holding the legs of the ZIF to the carrier is strong, but not that strong. It is relatively easy to break a leg free from the ZIF / MemCal connection. Using hot glue ensures that the ZIF is firmly in place and will stand up to your many removals and insertions of EPROMs. If you utilize this method then you will have to remove one of the MemCal retaining clips in the ECM because it contacts the ZIF.

Option #2 Explained: When using option 2 I used the following parts to construct the adapter...

34-Pin Wire-wrap protected header
Source: Digi-Key
Price: $4.46

Use a dremel and cut off as many pins as necessary in order to leave 2 rows of 14 pins (total of 28 pins). Using the 34-pin header mentioned above, I had to cut off a total of 6 pins (or, 2 rows of 3 pins). What you are trying to achieve is to make sure that all legs extending from the EPROM soldered to the MemCal join to a pin on the adapter you are making. Since the EPROMs have 28 legs (14 legs on each side), you need an adapter that has 28 pins with 14 pins on each side. Cut off any and all other pins. I also removed the sides of the header in order to make the adapter easier to use. Once you have cut off the necessary pins you will need to bend each row of pins slightly outward in order to be able to fit the adapter into the Programmer. The pictures previously presented provide a reference for this.

When utilizing this option and NOT using AT29C256 chips (which I highly recommend if you decide to use this method!) I have been asked many times how I erase the EPROM if it is still attached to the MemCal. The main reason that this question comes up is because the entire MemCal will not physically fit into the EPROM eraser. Also, there is usually a low tech safety mechanism on EPROM erasers that prevent the UV light bulb from shining unless the door on the eraser is closed. The door cannot be closed when placing a MemCal into the eraser. Normally, this is great. But, it can be frustrating when trying to erase an EPROM that is still in the MemCal. However, since EPROM erasers usually employ a low tech defeat mechanism (especially the Datarase), it is relatively easy to bypass once you work with the unit. However, please follow the warning previously outlined. Click here for a picture of the MemCal in the DataRase. Do not look at the UV light bulb! Do not expose your skin to it either! I usually place the DataRase in an 'abandoned' room. I close my eyes, turn on the unit, run out, and shut the door upon leaving (to ensure no pets or children wander into the room). I come back 15 minutes later. My unit has an automatic shutoff so when I return the UV light has already been turned off. Another method that has been suggested is to cut a hole in the cover of the unit just big enough to slip the MemCal into the chamber. This method is nice because it allows the original cover to engage the safety mechanism and because it keeps most of the harmful UV light inside the unit. However, you will have to be willing to cut a hole in the sliding cover. Remember, if you decide to use the AT29C256 chip then you will not need to worry about the UV eraser and the hazards of this step because the programmer will automatically erase the chip before it programs it. Again, this author highly recommends the use of AT29C256 chips if you decide you wish to pursue this method.

Another popular question is whether the UV light will hurt/destroy the limp home mode chips and/or the ESC filter on the MemCal. The answer is no. UV light will not harm these components of the MemCal.

Also, for your information, the current GM (AC Delco) part number for a new MemCal unit for all 1990-1992 350 F-Bodies is 16151348.

Step 10 marked with '**' is the step that requires a lot of learning on your part. You will need to become familiar with the editor that you are using. You will need to become familiar with what that editor gives you access to inside of the BIN. You will need to learn the acceptable changes for the various parameters and tables in the BIN. You'll need to research and/or learn how and what to change for various engine changes. You'll need to research and/or learn how and what to change for various drivability problems. Pay important attention to the 2 sections of this article entitled: 'Important Information for Beginners' and 'Modifying the BIN'. These sections will give you a head start on this task.

How difficult is it?

Let me break it down again:
Pull the chip from the ECM.
Read the chip using the programmer.
Save the BIN.
Open the 'other' software.
Load the BIN along with the calibration file.
Make the necessary changes and save the new BIN.
Load the programmer's software and load the new BIN.
Put a blank chip on the burner and program it.
That's it.

It is not difficult nor time consuming to program new chips. But, you must do the research and you must invest time to learn. You can program a new EPROM in a matter of a couple of minutes. But, the research in learning how and what to modify in the BIN can be extremely time consuming (and at times frustrating). On the other hand, the rewards are nothing short of spectacular. The next section covers this issue in more detail.

Important information for beginners

Presented below are several references that will give you a jump-start on changing a BIN's parameters and tables. Read through these links ... then read through them again.

Internet Links
Grumpy's tuning tips: http://www.diy-efi.org/diy_efi/oem/gm/tunetip.html
Grumpy's Programming 101: http://www.diy-efi.org/gmecm/papers/prog_101.html
GMECM FAQ: http://www.diy-efi.org/gmecm/faq/
GMECM: http://www.diy-efi.org/gmecm/
Thirdgen.org PROM Forum: http://www.thirdgen.org/techbb2/forumdisplay.php?forumid=16
TRAXION's Tuning VE Curves: http://www.thirdgen.org/techbb2/showthread.php?s=&threadid=39254
Michael Davis' Page: http://www.eecis.udel.edu/~davis/z28/
Ludis' Page: http://www.cruzers.com/~ludis/
ECMGuy's Page: http://www.geocities.com/ecmguy.geo/
Mr. Gasket's EFI Tuning PDF: http://www.mrgasket.com/ftp/pdf/EMIC.pdf
LJ's LT1 Page: http://para.noid.org/~lj/PCM%20Tutorial/PCMtutorial.htm

Helpful Books

  1. Jeff Hartman,"Fuel injection - Installation, Performance tuning, Modifications", Publisher Motorbooks international.
  2. Watson, Ben, "How to Repair and Modify Chevrolet Fuel Injection", Motorbooks International.

Mailing Lists
A very good source of information besides what I have presented above can be found by joining mailing lists. The most informative is the GMECM mailing list located at http://www.diy-efi.org/subscribe.html. There are many members of this mailing list who have years of experience burning chips for ALL types of automobiles. You can learn a lot from them. There is also a mailing list for TunerCat located at http://www.topica.com/lists/TunerCAT.

Modifying the BIN

Inevitably, once an individual understands this article and understands how to use all of their new PROM equipment, the following type of question is posted to the PROM message board or the GMECM mailing list...

Question: What do I modify in the BIN for my F-Body 1991 350 TPI that has 24lb injectors, 58mm TB, TPIS MiniRam intake, AFR195cc heads, LPE 219/219 camshaft, SLP 1-3/4" headers, catback exhaust, 180 thermostat, 4.10 gears, 2400 stall converter, and a shift kit!?!!???
Answer: If only it were that simple. In my experience a newbie PROM programmer wants to immediately jump in and make the 'perfect' chip for their setup. But, it is not that easy ... not even close. This new chip may take you months to get correct. Although you can program a new PROM in a matter of a couple of minutes, it takes significantly longer to develop that BIN so that it will work with your new setup. Again we arrive at my previous comments in the 'How you do it...' section of this article. The process of modifying a BIN to work perfectly with your car requires research, experimentation, time, and patience. You will probably burn 10-200 chips to get your calibration correct depending on how radically different your new setup is from your old setup and depending on how much you know. Again we see research, experimentation, time, and patience (where research and experimentation are the ultimate keys!). The more you learn the quicker you become at developing the correct BIN. The more you learn the more doors that are opened. Begin your research by going through all of the links in this article several times. You'll also want to read the previous posts on the PROM message board. Finally, the GMECM mailing list is the ultimate mailing list for these topics and there are archives that go back years. The archives alone act as a library to answer almost every question imaginable. The archives are located at ftp://ftp.diy-efi.org/incoming/ and are entitled 'GM_ECMArchives.zip' and 'DIY_EFIArchives.zip'. With all that said, let me break down the original question into a couple of other questions that you should be asking yourself...

  1. I am using 24lb injectors. What do I modify in the BIN to compensate for larger injectors?
  2. How does a bigger camshaft affect the fuel curve?
  3. I need the ECM to turn the fans on sooner due to my use of a 180 thermostat. What do I modify in the BIN to do that? Are there any other considerations of running a 180 thermostat?
  4. What am I seeing via a scan tool? Any knock retard? What are the BLMs at various conditions?
  5. Modifying the air intake of the stock TPI to a MiniRam and 58mm TB will have what affect on the airflow characteristics of the engine?
  6. What do my spark plugs look like?

Some of these questions apply directly to how you modify the BIN. Others questions are theoretical questions that relate to general engine theory. Other questions are reality questions that determine exactly how your engine is running at this point in time. In order to program PROMs successfully you will need a general understanding of engine theory and you will need a way to determine how your engine is currently running. These yield a great foundation from which you can learn more when conducting your research and doing your experimentation.

My recommendations for a new PROM programmer (who is already in the process of conducting all of their research) is to begin very slow. This means beginning with the easy stuff. Most BINs can be broken down into 3 elements that the tuner (that's you!) has available to them. Later on in life you will find that there are more than 3, but, for right now, we'll say there are three main elements: flags, constants, and tables.

Flags are switches. They have only two working values (like a light switch: ON and OFF). Flags are things like...

  1. Enabling/Disabling Functions (VATS, etc)
  2. Enabling/Disabling Diagnostics (EGR, VSS, etc)
  3. Switching between one element and another (Auto or Manual transmission?, etc)

Constants are single values. Constants are things like...

  1. Fuel Cutoff speed (mph)
  2. Fuel Injector flow constant (lb/hr)
  3. MPH for Torque Converter lockup
  4. Fan On/Off Temperatures (deg. C)

Tables are groups of values in relation to other variables. There are two-dimensional tables (2D) and three-dimensional tables (3D). Examples of BIN Tables are...

  1. Pump Shot vs. Differential TPS (2D Table)
  2. Target Idle RPM vs. Coolant Temperature (2D Table)
  3. Main Spark Advance vs. RPM vs. Load (3D Table)
  4. Volumetric Efficiency vs. RPM vs. MAP (3D Table)

In my opinion, the order of difficulty in terms of modifying the BIN is: flags, constants, 2D tables, and 3D tables. I previously stated to begin slow. Well, if possible, begin your experimentation with the flags, move on to constants, then 2D tables. Finally, work on the 3D tables. This is a good approach because it gets you accustomed to the overall procedure of modifying a BIN which is to research the changes, make the changes, burn the PROM, and evaluate changes. It also gets you accustomed to working with your new software, your new equipment, and your automobile.

Lets now examine the 'radical combination' previously suggested (1991 F-Body 350 TPI that has 24lb injectors, 58mm TB, TPIS MiniRam intake, AFR195cc heads, LPE 219/219 camshaft, SLP 1-3/4" headers, catback exhaust, 180 thermostat, etc)...

The car is equipped with a TPIS MiniRam which does not have EGR. Most likely the owner is experiencing a check engine light that yields a code pointing to the EGR not functioning properly. I would suggest beginning with disabling the EGR diagnostic in the BIN, burning this new BIN, and evaluating the change to your car. If all goes well you will no longer get a check engine light corresponding to a malfunctioning EGR valve. You have now successfully worked with flags. Move on to constants.
The above combination indicates a 180 thermostat. The owner most likely experiences around 180 engine temps while on the highway but 220 engine temps when in traffic. This is because the BIN doesn't activate one of the engine fans until a much higher temperature. Change the BIN's fan on/off temps to work with your 180 thermostat (maybe a 190 ON value and a 183 OFF value). Burn the new BIN and evaluate your changes. Does the fan come on sooner now? If so, at what temperature does it come on? What temperature does the fan go off? If all goes well the fan will come on at 190 F and off at 183 F. At this time you may have other questions such as: Why is only one fan coming on when I have two fans? or My temperature guage in the dash doesn't display accurately? What are the answers? Research. Research the answers. These are easy questions that most thirdgenners know and have been covered many times in the 'other' messageboards. If you have no other questions then modify other constants in the BIN such as the Fuel Injector Flow constant in order to work with the 24lb injectors. When you feel 100% comfortable with the flags and constants then move on to the 2D tables.
A reasonable place to begin with 2D tables for the above combination is with the Target Idle RPM vs. Coolant Temperature table. The bigger cam may need a higher idle speed. However, unlike the constants you will have to change multiple values. There is an idle speed setting for many different coolant temperatures. Make changes to the table, burn a new BIN, and then evaluate the changes. Did the car idle at your new settings for the given coolant temperatures?

3D Tables? I'll stop here. Describing how and what to tune for a specific combination of modifications is a huge discussion. We have only touched on a couple of changes above. There are numerous changes that would have to be made for that combination. One could write an entire volume of information on that very topic. The purpose of this article is to give you a place to begin. You now have that place to begin. You understand what it takes in terms of equipment and software to program your own PROMs. You have the references that you need for buying this equipment, modifying parts, and simple tuning procedures. You also have the references to research advanced tuning techniques.

Please note that everything that you need regarding advanced tuning techniques as they relate to BIN modification is not listed in an article for you to read anywhere on the internet. What you need to know cannot be found in some book that you can buy on Amazon.com. They exist in scattered articles, messageboard subjects, mailing list discussions, and old archives. There is no other way to learn these more advanced techniques besides researching these messageboards, mailing lists, archives, and scattered articles. It is now your job to get from point A to point B. If you ever get stuck on a topic and have seriously conducted the research to answer this topic then post a message to the PROM board (or the GMECM list). However, make your question extremely specific since broad questions such as the one in the beginning of this section often go unanswered. They go unanswered due to the fact that the answer would require a book as thick as an encyclopedia. Nobody has the time to write an encyclopedia. Furthermore, realize that those individuals who are disseminating the knowledge have probably been asked the same question 1,001 times and the answer is there on the internet either in the messageboards, in mailing lists, or old archives. Research and Experiment first. Ask questions later.

Scan Tools and Wide Band Oxygen Sensors

You cannot successfully program a better chip for your car unless you know what you want to change and why. That is a given. A great way for determining what you want to change is through the use of a Scan Tool. A Scan Tool is a tool that communicates with your car's ECM through the ALDL port and displays your car's current runtime statistics (such as O2 voltage, Coolant Temperature, Knock Retard, Air Temperature, Spark Advance, etc). Although it is not necessary to have a Scan Tool to successfully change your car's EPROM calibration, they can be extremely helpful because they let you see exactly what your ECM sees. Do you need more or less fuel? Do you need more or less spark? Do you experience any knock retard and if so, at what RPMs is the knock experienced? All of this information can be determined easily by looking at certain parameters that are displayed via the Scan Tool. In this writer's opinion - Beg, borrow, or steal a Scan Tool. They are invaluable and worth their weight in gold. However, it is important to note that some cars will benefit from a Scan Tool more than other cars. This is due to the fact that some ECMs transmit data at a faster rate across the diagnostic port. TBI equipped vehicles will benefit less than TPI vehicles (except for '85 TPI vehicles) due to the slower baud rate of their computers.

For example, a 0-60 run for a TPI equipped vehicle may yield around 25 data points. However, a 0-60 run for a TBI equipped vehicle will only yield 3 or 4 data points. ECMs with higher baud rates will update data across the diagnostic link much quicker. See the table at the end of this article to determine the baud rate for your F-Body.

Some of the more popular Scan Tools that cost money are presented below...
Diacom: http://www.rinda.com/auto/auto.htm
AutoTap: http://www.obdii.com
OTC: http://www.otctools.com
EASE: http://www.obd2.com/
AutoXRay: http://www.autoxray.com/index.htm
Datamaster: http://www.ttspowersystems.com/dm_dload.htm

Popular FREE ALDL software can be found via the following links:
Craig Moates' Software: http://ice.prohosting.com/moates/gmecm/software.html
Jonas Bylund's 160 Baud WinALDL: http://w1.601.telia.com/~u60113744/software/winaldl/winaldl.htm

To use some of the programs above (most notably the FREE programs) you will need a special cable that connects your laptop computer to the car. Check out AKM Electronics or Steve Ruse. Both of these companies make these cables. If you don't want to spend money on one of the 'special' cables then you can build your own through directions that are readily available on the Internet.

Link to AKM Electronics: http://www.mindspring.com/~amattei/akmelect.htm.
Link to Steve Ruse: http://www.geocities.com/steve3034/cables.html

Link to sites that have directions on how to build a cable:

Another extremely useful piece of equipment is a Wide Band oxygen sensor. Oxygen sensors measure the amount of oxygen in your exhaust and report an air-fuel ratio (AFR) as interpreted through a voltage measured at the Oxygen sensor in Millivolts. The stock oxygen sensor in all EFI F-Bodies is a one-wire sensor that is only accurate around a certain AFR - 14.7:1. Thus, when shooting for max power (lower AFRs) the stock oxygen sensor is not reliable and should not be used. This is where Wide Band oxygen sensors step up to the plate. They are very accurate across a wide range of AFRs. However, Wide Band oxygen sensors tend to be very expensive (in the neighborhood of $1000!). But, there is an alternative. That alternative is the DIY-WB project (Do-It-Yourself Wide Band). You can build your own Wide Band oxygen sensor for around $200! All the information that you need is located at http://www.diy-wb.com/. Please take note that this project is a non-profit project developed by members of the Do-It-Yourself EFI community through the EFI mailing lists at http://www.diy-efi.org. Be wary of other products that have used this information to develop a profit. Stick with the DIY-WB and support the DIY community!

Newbie Questions

The most frequent 'newbie' questions regarding PROM Burning are:

  1. Question: Which Scan Tool should I use? What are the Pros/Cons of each?
    Answer: This is an extremely difficult question to answer since there are so many tools available to the public. The more popular ones are listed above (Diacom, Ease, AutoXRay, OTC, and the Free Software). However, all of these programs can be arranged into 2 categories: laptop scanning software or handheld scanning unit. The first question that you must ask yourself is if you have access to a laptop. If you don't have access to a laptop then you can only consider one of the handheld units (AutoXRay, OTC, etc). If you do have access to a laptop then ask yourself how much money you have available to purchase a Scanning Program. Depending on your budget you will either need to go with the Free Software or a program such as Ease, Diacom, etc. A general rule of thumb is that the handheld units give you less flexibility and less functionality. So, keep that in mind when buying a handheld scanning unit such as AutoXRay or OTC. For example, using the 'Record' feature of the AutoXRay will only give you one datapoint every second. Contrary to this, laptop scanning software will yield many datapoints each second while in record mode. This may not sound like a big deal. However, when doing a 0-60 run with a total of 6 seconds from 0-60 the AutoXRay will only yield 6 datapoints whereas Diacom or Ease will yield possibly 100. This is a huge difference. Another example of this decreased flexibility and functionality is that many of the laptop scanning programs have options that allow you to graph the data, export the data, print the data, etc. Graphing is invaluable in terms of plotting one engine condition vs. other engine conditions. Furthermore, since the laptop scanning software shows you the ECM parameters on the laptop's screen, you have the ability to view many parameters at one time. The handheld units will usually only display one parameter at a time. In defense of the handheld units they are much cheaper and require nothing else to communicate with your ECM. I began my scanning experiences with the AutoXRay handheld scanning unit. Later, when I acquired a laptop, I purchased Diacom. The difference in terms of flexibility and functionality is night and day. It is important to note, however, that if you are going to use laptop scanning software then the old addage 'you get what you pay for' rings true. Programs such as Diacom, Ease, and Datamaster cost money. These companies get paid for adding useful features and functionality to their programs. In the past this has meant that these programs offer more flexibility, more functionality, and more user support than their free software counterparts. However, this is slowly becoming not true. Both Craig Moates' and Jonas Bylund's free ALDL software are very popular among the DIY crowd and both are very functional programs (and get even more functional as time progresses). All free software programs require you to make or buy a cable that can be used to connect your laptop to the ECM's communication port (ALDL connector). On the other hand, some of the programs that cost money (like Diacom) come with a cable (or multiple cables to connect to various automobiles). The differences between Diacom, Ease, and Datamaster are often the subject of conversation. However, if you are set on buying laptop scanning software then you can't go wrong with any of these. The only real questions to ask yourself regarding these programs are: What operating system exists on my laptop and how fast is my laptop. If you are running DOS on your laptop or the laptop is slow (less than a Pentium 133) then choose Diacom. Diacom runs in DOS and can run on very slow machines (I've even heard of it running on a 286!). However, if you are running Windows and your laptop is speedy then go with Ease or Datamaster. The 'Windows' environment is hard to beat. In the end, your decision will be based on the availability/type of the laptop and your budget. Just keep in mind the information presented above when making your decision.
  1. Question: Which Editor should I use? What are the Pros/Cons of each?
    Answer: Highly dependent upon several factors; namely the amount of money you have to spend, the type of computer you are using (including Operating System), the features you want, and what you feel comfortable using. I have limited this discussion to 3 Editors: WinBin, GMEPro, and TunerCat. However, be advised that there are other Editors out there. I am discussing these 3 because they are the most popular. If saving money is your most important consideration then choose WinBin. It is 100% Free of charge. If you are willing to spend money in order to receive more 'bells and whistles' and more support then choose either GMEPro or TunerCat. Both of these programs are excellent. If being able to run your Editor in a DOS environment is your primary concern then choose GMEPro. Both WinBin and TunerCat require a Windows based operating system. I quick list of pros and cons are listed below:

    Program Pros Cons
    Program is 100% Free
    Definition files are 100% Free
    Can create custom definition files
    Definition files are few and far between
    Definition files are harder to create
    Patches/Fixes by the author take much longer
    No Graphing or Compare feature
    Good Support
    Solid Program
    Runs on slow DOS laptops with few problems
    Can create custom definition files
    No Graphing or Compare feature
    Each Definition file costs more money
    DOS based environment is antiquated for some
    $80 for Editor (1 Definition file included)
    $50 for each Definition file
    $100 for info to create custom Definition files
    Great Support
    Solid Program
    Compare feature
    2D and 3D Graphing feature
    Many more Definition files available
    Can create custom definition files
    Runs best on faster machines (Pentium 133)
    Each Definition file costs more money
    $70 for Editor
    $20 for each Definition file
    $40 for Definition file Editor
  2. Question: Why can't I read my BIN with the demo version of TunerCat?
    Answer: The evaluation version of TunerCat available on TunerCat's site is delivered with the $42 definition file. This definition file is for a TBI Truck ECM (1228747) and, therefore, does not work with ANY F-Body BIN. To work with a '85-'92 F-Body BIN you will need a TunerCat Definition file that matches the BIN you are attempting to use ($1F, $32, $32B, $6E, $8D for TPIs or $4D, $61 for TBIs as specified in the table at the end of this article). This makes the evaluation of TunerCat difficult because the definition file that you will need for your F-Body BIN is not readily available unless you buy it from TunerCat. However, you can always send TunerCat an e-mail and request a Demo copy of the definition file that you need. In many cases he has supplied the necessary definition file for evaluation purposes. FYI, at the time of this writing the price for the definition file is $20. Please visit TunerCat's site for more information on purchasing the definition file. An alternative to buying the definition file for evaluation purposes is to evaluate TunerCat for the TBI Truck ECM (1228747). You can obtain a 747 BIN file from the 'diy-efi' site. There are many 747 BINS located at ftp://ftp.diy-efi.org/pub/gmecm/bin_lib/1227747%2042/

  3. Question: Where can I get the definition files?
    1. TunerCat - TunerCat Definition files are called TDFs and are delivered with a '.tdf' file extension. They are only available through TunerCat at a price of $20 each. Please visit TunerCat's site for more information on purchasing the definition file.
    2. WinBin - WinBin Definition files are called ECUs and are delivered with a '.ecu' file extension. In most cases the actual filenames contain the mask (either 8D, 6E, 32, or 32B) along with some type of version number. These files are available in several locations. Keep in mind that since ECU files are free and easily modified, they tend to be available at many locations. The most popular locations for these files are:
      DIY-EFI Site at: ftp://ftp.diy-efi.org/incoming/.
      ZaphodB's site at: http://www.area51.org.il/~zaphodb/gmecm/.
      Craig Moates' site at: http://ice.prohosting.com/moates/gmecm/software.html.
    3. GMEPro - GMEPro Definition files are called EPEs and are delivered with a '.epe' file extension. These files can be obtained through contacting Terry at terryk@foothill.net.

  4. Question: Where can I get a BIN?
    Answer: I would first suggest that you read the BIN from the chip in your car. If you aren't willing to do this then there are several places on the internet that have BINs for public download. Two of the more popular ones are listed below...
    1. GMECM BIN Library: ftp://ftp.diy-efi.org/pub/gmecm/bin_lib/.
    2. Michael Davis' Page: http://www.eecis.udel.edu/~davis/z28/.

  5. Question: My BIN won't load into the program or the PROM data appears wrong. What is the problem?
    Answer: The biggest reason that this occurs is because someone is attempting to utilize the wrong defintion file. Ensure that you have the correct definition file selected/loaded into the program. If you are sure that you have the correct definition file selected then try another BIN that is of the correct Mask. It is possible that you are attempting to work with a corrupted BIN file.
  6. Question: What BIN should I start with? Should I start with the BIN that I downloaded from my chip or is there a better place to start?
    Answer: In most cases you should start with the BIN you downloaded from your chip. However, the general rule of thumb is that you want to use the latest BIN that GM released for your make/model vehicle. Two of the most notable BINs for F-Bodies are presented below:
    1. 1986-1989 TPI F-Body with a 350ci Engine and automatic transmission - The best BIN to start with is the ARAP BIN. The ARAP BIN is a $6E binary developed by GM and used in the '89 TPIs that were delivered to the press. This BIN is a plug and play situation for the 1989 350ci Automatic F-Bodies since they are already running $6E code. For the '86-'88 F-Bodies you will need to either unplug your cold start injector or just use a cold start injector plug kit since the $6E binary gets rid of this piece of equipment (cold start injector plug kits are available through either Accel or Arizona Speed and Marine). For all MAF cars you will also need to make sure that the fans are set to "Normal Operation" since the stock ARAP has this operation reversed. This BIN can be found at both Craig Moates' page and ZaphodB's page as well as the GMECM BIN Library.
    2. 1990-1992 TPI F-Body with a 350ci Engine and Automatic Transmission - The best BIN to start with is the AUJP BIN. This BIN is available at ZaphodB's page as well as the GMECM BIN Library.

  7. Question: Where do I start? What do I modify in the BIN? How do I know what to change?
    Answer: Read the sections entitled Important information for beginners and Modifying the BIN located previously in this article.

How EPROMs work

At this point I would suggest learning the specifics behind what a PROM is and how they work. Xtronics has done a wonderful job at covering this in detail. For a full description on what PROMs are and how they work follow this link...

EPROM Reference for TPI and TBI Thirdgen F-bodies

ECM, EPROM, and Calibration reference
Year (TPI eng.) 1985 1986 1987 1988 1989 1990-1992
ECM Type C3 P4 P4 P4 P4 P4
ECM ID 1226870 1227165 1227165 1227165 1227165 1227730
EPROM Type 2732 27C128 27C128 27C128 27C128 27C256
BIN Size 4Kb 16Kb 16Kb 16Kb 16Kb 32Kb
Mask (Calibration) $1F $32 $32B $32B $6E $8D
Engine Management MAF MAF MAF MAF MAF Speed Density
Baud Rate 160 8192 8192 8192 8192 8192
MemCal No Yes Yes Yes Yes Yes
Bare EPROM Yes No No No No No

Year (TBI eng.) 1988 1989-1992
ECM Type C3 C3
ECM ID 1228063 1228746
EPROM Type 2732A 2732A
BIN Size 4Kb 4Kb
Program ID (Calibration) $4D $61
Baud Rate 160 160
MemCal No No
Bare EPROM Yes Yes


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