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#425550903T
Holley 550-903T Terminator X LS1 MPFI Kit
$1,258.95
/each
Factory Shipped
$1,399.95
Save $141.00
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Product Summary
Universal Fit, 24x Crank Reluctor, 1x Cam Trigger
Rebates Available
See rebate detailsKey Specs
| MFG. Part # | 550-903T |
| Brand | Holley |
| Ignition Type | Factory GM |
| Tuner Style | USB/CAN Tuning Cable |
| Throttle Style | Cable Driven |
Need To Know
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Holley 550-903T Details
Take control of your LS engine with Terminator X! Don't settle for a junkyard ECU with a cumbersome tuning interface when you can have complete control of your engine, self-learning fuel strategies and the proven, race-winning technology of Holley EFI at a budget-friendly price!
Terminator X features real-time fuel learn, high impedance injector drivers, an integrated 1bar MAP sensor, and 4 programmable inputs and outputs. The inputs and outputs are ideal for electric fans, boost control solenoids, progressive nitrous control, and much more. Terminator X comes fully loaded with base maps for common LS engine combinations to get you out of the garage and on the road/track fast. These Terminator X kits include a USB/CAN tuning cable instead of the 3.5" Handheld LCD, these kits require the use of the free Terminator X Software for initial setup. The Terminator X Software includes multiple base calibrations to choose from for either naturally aspirated or boosted engines. Also included is Holley EFI's industry-leading, easy to use software suite that allows full laptop access for advanced users. Whether you are building a budget beater or a boosted race car, Terminator X has the features and technology you need at a price that won't break the bank!
Features
- For GM LS1/LS6 engines with 24x crank reluctor - with EV1 Injectors.
- Real-Time fuel map learn, takes the guesswork out of tuning your base fuel table.
- High Impedance Injector Drivers will safely power most Stock LS injectors and Holley EFI Injectors. Injector support chart provided in the instructions (Will not control Low Impedance Injectors)
- All of the new Terminator X systems utilize the Bosch LSU 4.9 wideband to relay AFR information to the ECU for accurate reading and precise tuning control.
- On-Board 1bar MAP sensor is perfect for N/A or Nitrous engine combos. If your combination requires a 2+Bar, we recommend GM 12592525, and our adapter part number 558-416.
- MAP Sensor vacuum hose adapters (1/8th – ¼ and 3/16ths)
- 4 Inputs – 12v, Ground, 5v, and Frequency, for things such as additional pressure sensors, or activation triggers for nitrous activation, or a trans brake
- Boost Control – Boost vs Time, Boost vs Gear, Boost vs RPM, Boost vs Speed, Boost Safeties
- Nitrous Control – Single Channel of Wet or Dry, Progressive or Non-Progressive, Rich/Lean Safeties, and target Closed Loop AFR
- Advanced Tables – 4x 1D Tables, 1x 1D per Gear Table, 4x 2D Tables, 1x 2D per Gear Table, can be used for any custom tables you can dream up, such as Flex Fuel Sensor Offset Table, or a custom fuel or oil pressure safety!
- On-Board Diagnostic LEDS for: ECU Power – Engine Run – Wideband Status – TPS Calibration – Crank Signal –Cam Signal. Allow you to identify any Critical engine issues at a glance
- Includes CAN/USB tuning cable allowing you to configure your ECU and Tuning the engine in real-time.
- The compact ECU size allows you to mount it virtually anywhere. Remember, diagnostic LEDS must face up!
- Plug and play compatible with more Holley EFI accessories such as; analog-style gauges, shift lights, various modules, and coming soon, 12.3" digital dash support!
- Free EFI Tuning Software for complete control of your Terminator X power plant
- Includes: 24x LS Engine Main Harness - EV1 Injector Harness - Terminator X ECU - ECU Main Power Harness - Bosch LSU 4.9 Wideband Oxygen Sensor - Input/Output Harness - and assorted vacuum adapters.
Rebates
Holley IRS Sale 2026

Save 10% instantly on select products across the Holley family of performance brands during the annual Holley I.R.S.Tax Sale. Instant rebate period runs from February 17, 2026 through March 29, 2026.
CARB Warning
For race/ off road use or for use on pre-1966 vehicles.
CARB Warning
For race/ off road use or for use on pre-1966 vehicles.
Holley 550-903T Specifications
Holley 550-903T Specifications
| KEY SPECS | |
|---|---|
| MFG. Part # | 550-903T |
| Brand | Holley |
| Ignition Type | Factory GM |
| Tuner Style | USB/CAN Tuning Cable |
| Throttle Style | Cable Driven |
| GENERAL | |
| Crank Reluctor | 24x |
| Cam Trigger | 1x |
| Injector Connector | Jetronic / Minitimer (EV1) |
| MAP Sensor Included | Yes |
| Transmission Control | Yes |
| Oxygen Sensor Style | Bosch |
| GTIN Code | 090127074466 |
| Sold in Quantity | Kit |
Ratings & Reviews
Ratings & Reviews
Fitment
Fitment
1998-2002 Chevy Camaro
GM LS1
1997-2004 Chevy Corvette
GM LS1
1998-2002 Pontiac Firebird
GM LS1
2004 Pontiac GTO
GM LS1
