Programming a cars Computer.

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    Jan 5, 2012
    Welcome to the basement.

    Drag you up a chair. No, I can't help that the card table smells like gas and oil. The only rule here. Guns on safety at the table.

    This thread is gonna be about re-programming the ECM of a car. Specifically a 1994 GM, OBD-1 . The information crosses over to most electronically controlled motors. Be it Ford or Dodge.

    Theres not that much deference between the engine controls, sensors, how they programmed it to run among car makers. From Kia to toyota to BMW.

    My experience level at this is Zero. Before its all said and done. Anybody following along will learn what I do.

    Ill be using TunerCat OBD-1 pro tune. Datamaster logging.

    Heres the cables needed to interface with the cars ECM.


    The entry point. The cars Diagnostic port.


    Im using a beater lap top. If you think about it. This lap top is futuristic compared to a 1994 ecm.


    For referance. This is the ECM. This case contains a small mother board. Processor. By todays automotive standards its a Casio calculator wrist watch. Remember those dorky things?


    Next Ill post screen shots of the program. What things it reads, what it can change or not.

    The big thing to remember. A person can physically blow up the motor if certain things are changed too far. Or changed at all from the factory tune.

    I hope folks get alot enjoyment out of this. If youre a computer nerd but have no idea when it comes to cars. This is gonna surprise you. Stick around. Your skills will come in handy. Even more handy if your good at algebra.

    "Sent from a puff of smoke"
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    0   0   0
    Jan 5, 2012
    Definitions. Acronyms are gonna be everywhere.

    (Credit go's to, LT1 PCM Tuning - Tips & Tricks for DIY Tuning!. For this excellent definition write up.)

    • PCM/ECM: powertrain/engine control module, common terms for the computer that controls the fuel and spark delivery to modern engines, as well as their automatic transmissions
    • RPM: revolutions per minute, used for engine speed
    • TDC: top dead center, or the highest point the piston reaches inside its cylinder in the engine
    • Timing: used for the timing of the firing of the spark plugs from the coil; can be advanced (fired further before the piston reaches TDC) or retarded (fired closer to or after the piston reaches TDC)
    • BLM: block learn modifier (fueling correction)
    • STerm/LTerm: another name for BLM (see above); one is for long-term fuel correction, the other for short-term
    • AFR: air:fuel ratio, how much air is combusted per unit of fuel; the ideal AFR for balancing power production/MPG with reduced emissions is 14.7:1. More power is generally made with richer AFRs (less than 14.7:1), down to 12.6:1 or so, depending on the individual engine.
    • Vacuum/kPa: these are inversely proportional, meaning more vacuum equals lower kPa (100kPa = no vacuum, or atmospheric pressure)
    • WOT: full or wide-open throttle ("pedal to the medal"); ideally, this should also cause no vacuum or 100kPa
    • PE Mode: power enrichment mode; this is the PCM's modification for the car being at full or wide-open throttle (WOT). As more power is made at AFRs of less than 14.7:1, the default target AFR, this mode allows the engine to run at a richer AFR when at WOT
    • VE: volumetric efficiency, describes how well the engine can receive incoming air for combustion; so, for a given maximum of how much air could be ingested at a given point at normal atmospheric pressure (100kPa), the actual amount ingested is a percentage of that maximum. Obviously higher VE numbers mean better efficiency; 100 can be approached and even met and slightly exceeded with a naturally-aspirated engine; but numbers well over 100 are easy for forced induction setups like turbos and superchargers.
    • IAT: intake air temperature, used for the respective sensor; measures incoming air temperaturel used with the VE tables when in speed density mode to calculate fueling
    • MAF: mass air flow, used for the respective sensor; measures the mass of incoming air (grams/second) based on temperature changes on its filaments as airflow varies; will thus automatically detect elevation/air pressure changes, unlike the VE tables
    • Wide-Band/Narrow-Band O2 Sensors: two types of oxygen sensors, used for determing the air:fuel ratio (AFR) of an engine's combustion. Wide-band (WB) sensors are accurate along the entire spectrum (from very lean to very rich), while narrow-band (NB) sensors are only accurate along the narrow spectrum near stoichiometric AFR (14.7:1). Thus, NB sensors cannot reliably be used to tune at WOT.
    • Dyno: short for dynamometer, a device that measures power output; the most common is the chassis mounted version which measures torque and horsepower to the wheels of a vehicle, which accounts for the driveline losses of the transmission and rear-end. The other type is the engine dyno which connects directly to the crank of the engine. Dynos are a great way to verify power changes due to tuning.
    • DFCO: deceleration fuel cutoff; is used when the car is moving and the throttle is closed. Affects "engine braking," as fuel is cutoff and a reduced amount of spark advance is used (spark retard) to slow the engine down when the throttle is closed at a high RPM
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    deplorable malconent scofflaw
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    Nov 11, 2008
    Austin - Rockdale
    I'm not sure I'll ever need to tune an OBD-1 car, but I'm interested in following along.
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    Jan 5, 2012
    It doesn't have to be obd1. The concepts are the same. Air fuel ratio, timing, engine control.

    Studying this stuff I've found entire forums of nothing but tuning the ecm. They listed bin files of most GM cars. (Stock tune). I can download a stock 1995 lt1 corvette tune. Or a 2500 pick up.

    If my MAF sensor gives me grief. I can simple turn the ecm to speed density. Adjust the fuel tables and I'm gtg in the same elevation. Ford and Dodge also use both methods. A popular upgrade to the old stock lt1 injectors is modern Ford Bosch injectors. They function the same with either computer. Ford or GM.

    They all hysteresis function. Open loop, close loop...Just use different ways to control it.
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    Jan 5, 2012
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    TGT Addict
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    Jan 24, 2011
    Grid 0409
    Since you are from Killeen, this might be interesting:

    There was a community college on U.S. Hwy 190 over by West Fort Hood. The locals called it "Harvard on the Highway."

    Back in 1988, they were experimenting with microwave energy. Seems every time they ran their experiments, a bunch on late model vehicles would stall either on the highway, service road, or overpass from Fort Hood.

    The microwave tests were so intense and broad, that they either fried the ECM's or interrupted engine control inputs for miles around.

    Always seemed to happen at the afternoon rush hour.

    I was lucky -- I drove a '67 VW Beetle in those days.


    TGT Addict
    Lifetime Member
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    May 25, 2009
    So what is your goal here? More power? (that's usually the reason behind tuning). Just keep in mind that bad tuning can do some bad things. In certain cases, it can even install Windows in your block. (as in hole).

    I'd encourage you to know the limits of cylinder pressure, strength of rods, head bolts, etc. before trying anything extreme.



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