Guide updates and tuning notes by email → Follow us
Plan a swap

Home › Q&A › Tuning

How do you transfer injector data correctly when swapping to larger injectors at a different fuel pressure?

Enter the injector maker's full characterization for your exact injectors — Flow Rate vs kPa, Offset vs Volts vs Vacuum, Short Pulse Adder/Limit, and Min Injector Pulse — then rescale only the flow-rate table to your rail pressure with new flow = old flow x sqrt(P_new / P_old) per cell, using net (differential) pressure at each vacuum point unless the regulator is vacuum/boost referenced. Gen IV files reference Delta MAP, so 400 kPa in the tune equals 0 kPa on a Gen III — confirm lb/hr vs g/s units match before pasting, and never tune around wrong injector data.

Last updated

Who this applies to

  • Computers: P01, P59, E38, E67, Terminator X
  • Engines: LM7, LQ4, LQ9, LS1, LS2, LS3, LS6
  • Transmissions: all
  • Years: 1999-2013
  • Not for: Direct-injection Gen V LT (different injector model)

Gen III P01/P59, HP Tuners

  1. Engine > Fuel > Flow Rate vs kPa: enter the maker's flow data — flat for vacuum/boost-referenced regulators, sloped for deadhead rails flat (e.g. 25.2 lb/hr) or sloped (e.g. 24.5-27.1 lb/hr)
  2. Engine > Fuel > Offset vs Volts vs Vacuum: enter the maker's offset data
  3. Enter Min Injector Pulse, Short Pulse Adder, and Short Pulse Adder Limit
  4. For oversized injectors: cut Min Fuel Milligrams under the Transient Fuel tab so idle isn't pig rich 0.041 to 0.008-0.010
  5. Rescale Ford-rated data (39.15 psi) to your rail pressure with Tools > Unit Conversion > Fuel Injector Calc 39.15 psi reference

Gen IV E38/E67, HP Tuners

  1. Engine > Fuel > Offset vs Press vs IGNV: enter maker's offset data
  2. Engine > Fuel > Flow Rate vs Press: enter maker's flow data (Delta MAP referenced — 400 kPa in the file equals 0 kPa on a Gen III) 400 kPa = 0 kPa Gen III
  3. Enter Short Pulse Limit, Short Pulse Adder, and Min Injector Pulse

Rescaling flow data to a different rail pressure (any controller)

  1. Scale the 0 kPa cell by sqrt(P_new / P_old) — e.g. 58 to 43.5 psi gives 0.866
  2. Scale vacuum cells by net (differential) pressure — e.g. the 80 kPa cell scales by 0.890 for 58 to 43.5 psi — unless the regulator is vacuum/boost referenced, then the raw ratio applies to every cell
  3. Verify rail pressure holds steady under load (58 psi returnless target) with a gauge before finalizing 58 psi steady

Careful

  • Against Bernoulli's principle — plagiarized/factored data sheets have circulated.
  • Don't crank base pressure to 90-100 psi to avoid buying injectors — stock-style injectors weren't designed for it.

More in tuning fundamentals, or build a checklist for your swap with the tune checklist tool.

Go deeper

Check this first

  1. Confirm flow units match (lb/hr vs g/s) before pasting — the most common data-entry error
  2. Log injector duty on a full WOT pull — if peak is over ~85%, size up before finalizing fueling
  3. Verify rail pressure holds steady under load with a gauge — a pressure drop is a pump/wiring problem, not a table problem

Try this, then this

  1. For your exact part number and enter all tables — Injector data is the foundation; tuning around wrong data never converges. Worked if: Trims settle near zero across the board
  2. Rescale flow to your rail pressure with sqrt(P ratio), using net pressure per vacuum cell — Pressure changes flow; the 0 kPa cell uses the raw ratio, vacuum cells use differential pressure. Worked if: Trims stay flat across vacuum instead of drifting
  3. Cut Min Fuel Milligrams for oversized injectors and recheck idle — Fixed minimum fuel delivery can drown idle even with VE pulled down. Worked if: Idle trims come back into range

How you know it's fixed

  • Fuel trims within +/-5% (+/-10% acceptable)
  • Duty under 85% at peak
  • Idle not pig-rich with big injectors

Key numbers

WhatValue
Flow scaling lawnew flow = old flow x sqrt(P_new / P_old)
80 kPa cell scaling example (58 to 43.5 psi)0.890
Vacuum-cell scaling ruleuse net pressure unless the regulator is vacuum/boost referenced
Physical basischange in flow proportional to sqrt(pressure ratio)
Tables to changeFlow Rate vs kPa, Min Injector Pulse, Offset vs Volts vs Vac, Short Pulse Adder Limit, Short Pulse Adder
Injector duty ceilingunder 80-85% peak
Whole-characterization rulemove every injector table together
Unit check before pastinglb/hr vs g/s
Ford injector reference pressure39.15 psi (rescale to GM 58 psi rail)

Every option we know of

Maker / productPart #FitsPriceWhereStatus / notes
Injector Dynamics
ID injectors with HP Tuners characterization spreadsheets		LS applicationsinjectordynamics.comIn production
Buy from authorized dealers; copied/factored data sheets have circulated
Fuel Injector Clinic
FIC injectors with HP Tuners data		LS applicationsfuelinjectorclinic.comIn production
On E40, injectors over 63 lb/hr need double-stoich/halve-IFR scaling

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: Free in software; a fuel pressure gauge is the only tool needed. Budget an hour for data entry and verification.

Something wrong on this page? Tell us