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LS tuning fundamentals

How the computer decides fuel and spark, and the measurements a tune is built on: VE and MAF airflow models, closed loop and fuel trims, wideband sensors and injector data.

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Fundamentals, from the sources

Paraphrased from the linked sources (30 points). Specifics depend on your computer and operating system.

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• LS Gen III/IV; 1997-2013: The Sniper EFI system requires a high-pressure fuel pump capable of 60 psi, with a built-in regulator factory-set at 58.5 psi, and at least 3/8-inch feed and 5/16-inch return lines. Holley
• LS Gen III/IV; 1997-2013: The wideband oxygen sensor should be mounted where it samples a good average of one bank's cylinders, slightly after they merge; with long-tube headers that means roughly 1-10 inches after the collector, with at least 18 inches of exhaust pipe downstream of the sensor. Holley
• LS Gen III/IV; 1997-2013: If the vehicle has catalytic converters, the oxygen sensor must sit between the engine and the converters, and it must never be installed at the bottom of the exhaust tube so condensation cannot enter the sensor. Holley
• LS Gen III/IV; 1997-2013: The Sniper's hot idle target is the RPM it targets once coolant temperature is above 160 degrees Fahrenheit. Holley
• LS Gen III/IV; 1997-2013: Converting to EFI will not fix mechanical problems: the engine must have no vacuum leaks, correctly set ignition timing, and sound mechanical condition, because EFI cannot cure bad valves, damaged head gaskets, worn piston rings, or cracked leaking vacuum lines. Holley
• LS Gen III/IV; 1997-2013: Closed Loop status on a Holley ECU means it is adding or subtracting fuel to hold the target air/fuel ratio; the system is intended to run in closed loop almost all the time. Holley
• LS Gen III/IV; 1997-2013: CL Comp is the moment-by-moment percentage of fuel the Holley ECU is adding or removing to hit the target: a minus sign means fuel is being removed, no sign means fuel is being added, and it reads 0 percent in open loop. Holley
• LS Gen III/IV; 1997-2013: The Holley Target AFR changes with engine speed and load, and closed loop compensation continuously adjusts fuel so the wideband reading (AFR Left) stays near the Target AFR. Holley
• LS Gen III/IV; 1997-2013: Holley self-tuning (Learn) only runs when engine temperature exceeds 160 degrees Fahrenheit, the engine is in closed loop, and Learn is enabled; the status reads Learn when active and NoLearn when it is not. Holley
• LS Gen III/IV; 1997-2013: Idle is set on a fully warm engine: in neutral, adjust the idle screw until IAC Position reads between 2 and 10 percent, and do not attempt this below 160 degrees Fahrenheit. Holley
• LS Gen III/IV; 1997-2013: The Sniper's fuel prime shot fires 2.5 seconds after key-on; turning the key quickly without waiting skips the prime and can make the engine take longer to start. Holley
• LS Gen III/IV; 1997-2013: A practical self-tuning drive cycle: warm the engine past 160 degrees, drive varied speeds, loads, and gears with A/C on and off; when CL Comp sits near zero in an area, the self-tuning is considered complete there. Holley
• LS Gen III/IV; 1997-2013: Key-on/engine-off sensor baselines before first start: TPS should read 0 and sweep to 85-100 percent at wide open throttle, MAP should read 95-102 (as low as 75 at high elevation), and battery should be at least 12.0 volts. Holley
• LS Gen III/IV; 1997-2013: Holley recommends the first start use non-timing-control ignition, then setting static timing to 15 degrees with a timing light on the balancer before handing timing control to the ECU. Holley
• E38; LS Gen III/IV; 1997-2013: Closed loop is the built-in feedback control: the ECU reads the exhaust oxygen sensors, estimates the actual air-fuel ratio, and adds or removes fuel to bring the mixture back to its target. High Performance Academy
• E38; LS Gen III/IV; 1997-2013: Narrowband oxygen sensors are only accurate at the 14.7:1 stoichiometric ratio for pump gasoline; richer or leaner than that they are effectively useless for tuning. High Performance Academy
• E38; LS Gen III/IV; 1997-2013: A narrowband sensor cannot measure how rich the engine is at wide-open throttle under power enrichment, where the target is much richer than stoichiometric, so it cannot be used to fully tune the engine. High Performance Academy
• E38; LS Gen III/IV; 1997-2013: To properly calibrate an ECU across its operating range, a wideband air-fuel ratio sensor is required. High Performance Academy
• E38; LS Gen III/IV; 1997-2013: Short term fuel trim is an instantaneous correction based on an error that exists right now: if the engine is running too rich against the stoichiometric target, STFT removes fuel to drive it back. High Performance Academy
• E38; LS Gen III/IV; 1997-2013: If a short term trim stays negative for a significant period, the ECM decides there is an error in the calibration at that point and applies a long term fuel trim that absorbs what the short terms were doing, letting STFT return toward zero. High Performance Academy
• E38; LS Gen III/IV; 1997-2013: Closed loop control deliberately cycles the air-fuel ratio slightly rich and lean across the stoichiometric point, which is what makes catalytic converters work efficiently. High Performance Academy
• E38; LS Gen III/IV; 1997-2013: A good tuning target is closed-loop trims as close to zero as possible, ideally within plus or minus 3 percent, with up to plus or minus 5 percent tolerated before calibration work is warranted. High Performance Academy
• E38; LS Gen III/IV; 1997-2013: GM ECMs rely primarily on the mass airflow sensor, which directly measures the mass of air entering the engine so the ECU can pick the injector pulse width for a target air-fuel ratio. High Performance Academy
• E38; LS Gen III/IV; 1997-2013: The MAF sensor has some latency under transient conditions such as sharp throttle openings, which is why GM added a speed density subsystem to complement it. High Performance Academy
• E38; LS Gen III/IV; 1997-2013: Speed density tuning models airflow from a three-dimensional volumetric efficiency table indexed by manifold absolute pressure and RPM rather than measuring it directly. High Performance Academy
• E38, E67, E40, P59; LS Gen III/IV; 1997-2013: Early Gen III LS1 ECMs used a conventional built-in VE table, while later GM ECM generations moved to a virtual volumetric efficiency (VVE) system. High Performance Academy
• E38; LS Gen III/IV; 1997-2013: If you want to tune using only short term fuel trims, you must disable long term fuel trims first, otherwise the combined data will be inaccurate. High Performance Academy
• LS1; 2000-2013: EFI tuning software such as EFILive is a tool rather than a tune in itself: it reads, modifies, reflashes, and datalogs the factory ECU's operating parameters. LSX Magazine
• LS1; 2000-2013: A quality wideband oxygen sensor is required so you can read what the engine is doing in every driving scenario, and the tuning software can interface with many wideband brands. LSX Magazine
• LS1; 2000-2013: The VE table represents the engine's actual pumping efficiency at each point in its operating range: an engine is basically an air pump that is more or less efficient at different operating parameters. LSX Magazine

Next, size injectors and pump with the fuel system calculator, or read fuel, E85 & boost.

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