Guide to PROM Tuning

1. Guide to PROM Tuning Todd Pepmeier 15-May 2004

2. Basic Tools Diagnostic Software EASE, Datamaster, Diacom, TunerPro EEPROMs (or Ultraviolet Eraser for stock EPROM) Atmel 29C256 is a direct replacement EEPROM ($5 ea) � or use a UV eraser such as Datarase II � $39 EPROM Programmer Pocket Programmer II ($150), Moates� BURN1 ($75), Needham�s EMP-10 ($200), etc. Binary Editor program + definition file for your application TunerCat ($90) & �.TDF� files ($20) TunerPro (free) or WinBin (free) & �.ecu� files

3. Advanced Stuff Real-time EPROM Emulator For �on-the-fly� changes; Xtronics Romulator ($180) Multi-bin switcher Uses bigger EEPROM to store up to 16 different cals! ($55-$75) Wideband O2 w/datalogging For accurate air-fuel measurement; FJO inc ($600); D-I-Y (~$200) Integrated datalogging + emulator + EPROM Programmer all-in-one package Moates� AutoProm ($325)

4. How it Works Three parts to the GMP4 code Calibration data � tables and constants (�look-up data�) Program Code � 6000 lines of assembly language instructions RAM data � stored input/output values used by the program (ex: current spark advance or fuel correction values) Calibration data and Program code are stored on EPROM chip inside Mem-Cal Can be downloaded, saved as � .bin� (binary) files � 32KB size for most GMP4 code Bin files can be read with standard Hex editors Get used to base-16 math 0-9, A, B, C, D, E, F

5. How it Works Most all changes are done to the calibration portion 600+ items available Bit Flags Example: VATS Enabled (1=yes) Single values (constants) Example: Minimum Coolant Temp to enable CARS 2-Dimensional Arrays Example: Power Enrichment versus RPM table 3-Dimensional Tables Example: Main Spark Table

6. Summary of BFXB Calibration 130 items which define ALDL diagnostic data stream 120 � for fueling control, incl Closed Loop parameters 100 � error code parameters 60 � to control the Idle Air motor activity 40 � for Spark advance 20 � for Port Throttle & sec Fuel pump control 20 � for Cranking and Startup routines 100+ � for miscellaneous stuff (A/C, CCP, AIR, Fans, etc) 600 total items 90% of these work just fine the way GM designed it!

7. Program Code Assembly language instructions which are used to read input sensors, lookup calibration data, do calculations, and control output devices Essential to understanding how the various calibration items work Program executes in several loops running at various intervals from 6.25ms to 1 second Similar to other GMP4 code of late 80�s / early 90�s vintage ($8D mask, ANHT, from L98 application is very similar and thoroughly commented in public domain) Can be �disassembled�, or translated, with standard Motorola 68HC11 software tools

8. Interesting Findings Low Octane Spark Retard Permanently removes 5d of advance when persistent knock is detected. Restart will restore lost advance. Not in earlier cals. Not the same as normal knock retard feature, which recovers more quickly Pass-by Noise Control Can retard ignition timing up to 5d under very limited circumstances. Would rarely be activated under normal driving. Upshift Light Disabled on service cals by using high enable temp IAC Operation/Throttle Follower 60 calibration items and 1000s of lines of program code to control the IAC motor Throttle follower logic opens the IAC motor with the throttle blades; very slow decay rate Closed loop idle control (not fueling) tries to maintain idle speed within +/- 50 rpm

9. Throttle Follower graph

10. Interesting Findings BARO corrections Available but not used on most cals DFCO (Decel Fuel Cutoff) Cuts fuel flow on overrun (high vacuum) coast-down Injector Flow Rate Stock GM cal value is 22.78 lbs/hr (actual injectors are 19.5?) Closed Throttle Spark Spark advance is held at a constant value when throttle is closed and certain other conditions are met Closed Throttle spark does not use the main spark table This constant varies on the various model years from 14-24 degrees Can be disabled by clearing a bit flag

11. Interesting Findings Fueling Strategy Basic equation Inj Pulse Width = f (target a/f ratio, airflow, injector size) Modified by Closed Loop Correction Term (BLM, INT) Power Enrichment added for high load - 19% richer (12:1 target) Acceleration Enrichment added for rapid change in load (�pump shot�), then decayed out Can be fine tuned to optimize throttle response Tip-in lean condition can be seen on wideband

12. Fueling Routine Determine target A/F ratio Initially set at 14.7:1, richer for Power Enrichment, Open Loop enrichment Calculate airflow through the motor Using MAP and IAT, Volumetric Efficiency, and cylinder volume Based on airflow, determine fuel required to achieve target A/F ratio Based on injector size, calculate how long the pulsewidth must be Apply pulsewidth multipliers like Accel Enrich, or startup enrich, or batt voltage correction, etc. Scale final pulsewidth by 0.51 if secondary injectors active

13. Interesting Findings Snakeskinner Code Based on late �89, early �90 code (AUAH?) Open Loop (no O2 Sensors) Port Throttles always open (butterflies removed) 28 degrees WOT spark advance 1000 RPM idle speed Knock Retard completely disabled 7200 RPM fuel cutoff 2.5% lower cylinder volume constant Error diagnostics disabled for TPS, MAP, O2, Port Throttles, ESC, Valet Switch

14. Tuning Methods Make one change at a time, and test the results Take notes! Basic Changes Disable CARS (1-4 skip shift) by setting enable temp high Lower Cooling Fan temperatures Turn on 5-10 degrees above thermostat opening Change Spark Advance 4 tables (RPM<4000, RPM>4000, PT CLSD, PT OPEN) Stock usually around 25d max at WOT, can go to at least 28d Diminishing returns after around 32d on race gas Big dips in stock map around 3000-4000 rpm

15. Main Spark Table (PT OPEN)

16. 100 Kpa Spark Advance (PT OPEN)

17. 75 Kpa Spark Advance (PT CLSD)

18. Tuning Methods (cont�d) Other Changes Changes to base fueling 4 tables (RPM<2000, RPM>2000, PT CLSD, PT OPEN) Stock is pretty good in most cases Increase Volumetric Efficiency % to add fuel (decrease to subtract fuel) If no wideband data, shoot for BLM values of 128 (0% corr) If using wideband, can disable closed loop and tune in Open Loop mode. Generally want 14.5-14.7:1 ratio at low loads. Power enrichment is added around � throttle, at which point you should shoot for around 12.5-13.0, depending on what your car likes best

19. Stock Fuel Table (PT OPEN)

20. Custom Fuel Table (PT OPEN)

21. Tuning Methods (cont�d) Other Changes Reduce spark retard when intake temps get higher �91-�95 Default to Full Power Mode Requires 1 byte change in program code Improve knock retard handling (faster recovery) Raise Idle RPM Adjust Injector constant for larger injectors Adjust cylinder volume for 368-415 cid applications Fine Tune Power Enrichment & Accel Enrichment fueling Raise (or lower) Port Throttle Opening point Earlier is not always better!

22. Resources Websites www.diy-efi.org �White papers and archives www.thirdgen.org �DIY-PROM Discussion Board www.moates.net �Autoprom, blank EPROMs and bin-switcher tunerpro.markmansur.com �TunerPro software Mailing lists DIY-EFI GMECM Reading ANHT hac.pdf (fully commented L98 calibration) Turbo P4 document �detailed GM document explaining how a �P4� ecu works (available at diy-efi.org) Motorola 68HC11 instruction set (available at motorola.com)