This is Part 2 of the Gen 3 LS tuning start. If you haven’t watched Part 1 yet, start there — this picks up assuming you already have the vocabulary from it.

Where you should be before watching this

Part 1 was about getting the language straight, because that’s the thing that stops most beginners before they ever open a tuning file. Here’s the short version of what it established, so you’re not lost thirty seconds in.

The computer

PCM vs ECM — P is powertrain, E is engine. Roughly the same box. PCM controls more because powertrain includes the transmission and, on some cars, a couple of sensors in the differential. Plenty of cars say ECM even when it’s running the trans anyway.

The sensors that matter

MAP — manifold absolute pressure. Reads pressure in the intake, vacuum or positive.

MAF — mass airflow. Sits in the intake pipe with a heated element and measures how much air is going past by watching how much voltage it takes to hold that element at temperature.

Both sensors are answering the same question two different ways: how much air is in the cylinders right now.

O2 sensors — feedback on how you’re burning it. Short term corrects in the moment, long term learns the pattern and dials it in permanently.

EQ ratio — the air/fuel the computer is actually commanding. This is the final product, the thing the PCM is trying to deliver.

Spark — spark advance.

The two rules worth repeating

First: you need a wideband. A stock narrowband only resolves tiny changes around the sweet spot, because that’s all GM built it to do. If you’ve made real changes — a cam, more fuel — a narrowband cannot tell you whether you’re hitting your commanded ratio. This isn’t optional equipment.

👉 Innovate LC-2 wideband kit with Bosch LSU 4.9 sensor, and an OBDLink MX+ for talking to the PCM. Free software handles the rest — see Tuning Gen 3 for basically free.

Second: decide your goals before you touch a table. Set your equivalency ratio and power enrichment targets first. Everything downstream depends on what you’re asking the engine to actually do, so answering that badly means redoing the work.

If you’re not there yet

Go back to Part 1 — it covers all of the above properly, plus swap notes for things like a truck 6.0 going into a different car, when you have to tune the MAF versus leave the MAP alone, and where the primary VE table lives.

Still picking a long block? Best LS engine years for boost, and if you’re after Gen 4 rods specifically, here’s every GM vehicle that came with an LS and the year cutoff to look for.

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