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What do I need to buy and set up to tune a twin-turbo 408 LS with EFI Live — do I need a custom OS, and should I run MAF or speed density?

Buy an EFILive FlashScan V3 with the GM tuning option (a used V2 also works), plus a wideband, a 2- or 3-bar MAP sensor, and run speed density — a 408 twin-turbo will max out the MAF, and EFILive's free custom OS (COS3 for boost, COS5 adding 3-bar/nitrous/TPS VE) gives you boost VE and boost spark tables plus a proper open-loop AFR table (B3647). Do the AutoVE process: dial the VE in naturally aspirated first, then tune boost fueling and timing.

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Who this applies to

  • Computers: P01, P59
  • Engines: LQ4, LQ9, LS1, LM7
  • Transmissions: all
  • Years: 1999-2007
  • Not for: E38/E67/E40 (EFILive custom OS is a P01/P59 thing; Gen IV uses different tooling)

P01/P59 (0411 etc.), EFILive

  1. Buy FlashScan V3 scan-only (US$625) + GM Tuning option (US$450, includes 2 VIN licenses); a used FlashScan V2 also works US$625 + US$450
  2. Full-flash the matching custom OS (free, no VIN license needed): COS3 for 2-bar boost, COS5 adds 3-bar/nitrous/TPS VE
  3. Force SD: remove the MAF or set the MAF sanity/failure tests to fail immediately (C2901/C2902)
  4. Install a 2- or 3-bar MAP sensor and enter its scalars in Engine Diag > MAP
  5. Set open-loop AFR in B3647 (MAP vs RPM) and set PE rich before any boost pulls
  6. Run AutoVE: dial VE in N/A first, then move on to boost fueling and timing

Logging with EFILive

  1. FlashScan V2 logs standalone to SD card (black-box logging/flashing); V1 needs the laptop in the vehicle
  2. Feed the wideband into the V2 over RS-232 serial to avoid analog ground offsets

Careful

  • A wideband is required — do not do boost pulls on narrowbands.
  • Dyno time is strongly recommended for the WOT/boost portion.
  • Before AutoVE, guestimate the new VE and set OL/PE AFR richer to avoid going lean at high load.

More in fuel, E85 & boost, or build a checklist for your swap with the tune checklist tool.

Go deeper

Check this first

  1. Read the stock file and confirm your OS has a matching COS before buying anything
  2. Log MAF g/s on the current setup — if you're near 512 g/s, the MAF is done and SD is mandatory

Try this, then this

  1. Start with the stock OS, real injector data, and a wideband; get it running N/A first — Boost tuning on a broken N/A baseline blows engines. Worked if: Trims and VE sane off-boost
  2. Full-flash the COS and set B3647/PE rich before the first boost pull — Rich targets protect the engine while you gather AutoVE data. Worked if: Safe AFRs under boost from pull one
  3. Run AutoVE passes, extrapolating trends upward, finishing with WOT sweeps — The COS method corrects the whole VE surface systematically. Worked if: Fueling error near zero across MAP/RPM

How you know it's fixed

  • VE dialed in N/A with the wideband before any boost
  • Boost fueling hits the B3647 targets under load
  • No knock retard on boost pulls

Key numbers

WhatValue
Custom OS costfree, no VIN license needed
COS boost rangeup to 3 bar of boost in SD
COS3/COS5 on the 0411 PCMCOS3/02020003 (boost), COS5/02020005 (boost, nitrous, TPS VE)
Open-loop AFR table in COSB3647 (MAP vs RPM)
MAF fail in EFILiveC2901/C2902 fail immediately
GM tuning optionUS$450.00, includes 2 VIN licenses
MAF ceiling on early LS1 PCMs512 g/s
COS features2/3-bar MAP VE scaling, MAF-less true SD

Every option we know of

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Maker / productPart #FitsPriceWhereStatus / notes
EFILive
FlashScan V3 (scan only)		GM gas controllers incl. P01/P59US$625.00efilive.com/buyIn production
Needs the GM Tuning option added to flash
EFILive
FlashScan GM Tuning option		FlashScan V3/V2US$450.00efilive.com/buyIn production
Ships with 2 VIN licenses
EFILive
AutoCal V3 (blank)		Use with a tuner's FlashScan$650.00 USDtopgundieselperformance.comIn production
Blank — needs a tuner to load files; tuner needs your FlashScan serial
Wideband (AEM/Innovate/PLX)
Wideband O2 with serial output		FlashScan V2 serial inputIn production
Serial avoids analog ground offsets
MSD
3-bar MAP sensor		MSD-2313Universal 3-pinBuy
Summit Racing		In production

Prices are approximate as of September 2026. We list every option we know of, including small shops and used parts we can't link to. Confirm fitment with the seller.

Time and cost: FlashScan V3 scan-only US$625 + GM tuning US$450 (includes 2 VIN licenses); extra VINs US$125. Budget a full weekend for AutoVE plus dyno time for boost.

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