LS swap tuning help on HP Tuners

A Gen III/IV LS runs a speed-density (VE table) and a MAF-based airflow model at the same time, blending between them. The VE (volumetric efficiency) table is the engine's airflow map when the MAF is out of the picture or being overridden; the MAF table calibrates the actual sensor. Get either wrong and the fueling fights itself — surging, rich-lean oscillation, and fuel trims that swing wildly.

In a swap, the trouble is that your engine almost never matches the calibration's assumptions. A cammed 5.3 in a 3,200-pound car pulls different airflow than the truck it came from. Many swappers run MAF-less (speed density) to dodge intake-tube and sensor-placement headaches, which puts all the load on the VE table. TuneVault checks whether your VE and MAF tables agree with each other and with your fuel trims, and tells you which model your setup is actually leaning on.

Idle is where LS swaps go to die. A larger camshaft reduces manifold vacuum and reverts exhaust back into the cylinders, which the MAP/MAF sees as a load signal it doesn't expect at idle. The result is a hunting, surging, or stalling idle as the ECU's idle airflow and spark control chase a target the cam won't let it reach.

Fixing it means coordinating several tables: the commanded idle airflow, the idle spark vs RPM relationship (a steep spark-up-on-droop curve helps catch a sagging idle), the desired idle RPM, and the MAP-vs-VE behavior at low load. A bigger cam usually wants a higher target idle and more idle airflow. TuneVault looks at your idle tables together and flags the classic cammed-LS mistakes — too-low target idle, no spark stabilization, and a VE table that's lying to the ECU at low MAP.

Most LS and LS-based swaps are drive-by-wire, which means the pedal, the throttle blade, and the torque-management model all have to agree. When you drop an LS into a Miata, an S-chassis, a 4x4, or anything else GM never imagined, the torque tables and transmission expectations can produce sluggish tip-in, surge, or a throttle that feels disconnected. The fix lives in the pedal and throttle effective-area maps and in disabling or neutralizing torque management that assumes a GM drivetrain.

TuneVault checks your pedal-to-throttle mapping and torque-management settings for the dead spots and abrupt transitions that make a swapped car feel wrong. It also flags the DTCs you'll want to turn off — VATS/anti-theft, EVAP, rear O2s, and transmission codes that don't apply in a swap — so the car runs without a check-engine light it doesn't need. It won't, however, do a from-scratch first-start cal for you; a known-good swap base file is the right launching point.

Once it idles and drives, you dial in the airflow tables using fuel trims in closed loop and a wideband at wide-open throttle. Closed-loop trims let the engine correct toward stoich on its own and reveal where your VE/MAF tables are off; you then bake those corrections back into the tables until trims sit near zero. Wide-open throttle is open loop, so a wideband is the only thing telling you the truth up there.

This is exactly the workflow TuneVault supports: you log it, TuneVault reads commanded versus delivered AFR and your trims, and it tells you which VE or MAF cells to nudge and by how much. It is a copilot for a swap, not a substitute for a professional tuner on a high-strung build, and it never promises power figures. Verify wide-open fueling with a wideband before you lean on it — what you flash is your responsibility.