Take A Closer Look At Holley's Terminator X For GM Gen V LT Engines

10 min read

Take A Closer Look At Holley's Terminator X For GM Gen V LT Engines

10 min read

Holley’s engine control systems have been around for nearly forty years. The first Holley EFI systems, like the Pro-Jection and Commander 950, were groundbreaking and the latest Terminator X systems are continuing that tradition. With Gen-V LT engines from Chevrolet fully adopting direct-injection technology, the Holley Terminator X and Terminator X Max for GM Gen V LT-series ECUs are taking the world of engine swapping by storm. Building on the success of the LS-series Terminator ECM systems, the Gen V Terminator X and X Max hit all the points necessary to gain full control of your Gen V engine, as well as give you control far beyond that of a factory ECM. Input and outputs for additional components such as nitrous controllers, cooling fans, trans brakes, etc. make the Terminator X and X Max an attractive option for anyone looking to put the latest and greatest GM engine into a different vehicle platform.

Terminator X Gen-V LT swap

Once you finish the physical mounting of your Gen V LT-series engine, you have to get it running, and that means the dreaded wiring and ECM programming. Only it doesn’t have to be a nightmare, the Holley Terminator ECM system greatly simplifies the entire process.

Terminator X

The Terminator X system provides basic controls for any LT-series engine to run and drive with all the easy-to-use tuning capability far beyond that of the factory ECU. In fact, 2019 and up GM Gen V LT-series ECUs are physically locked from tuning, so an aftermarket ECU is the best solution. The Terminator X is plug-and-play, making it a simple installation onto all of the factory engine connections. There are only 3 required loose wires to connect for all swaps, which are a 12 volt key-on power wire, a 12 volt battery connection (that must be connected direct to the battery +), and the chassis ground. There are a few optional wires, including provisions for a fuel pump, tach output, coil out (for RPM signal inputs), and points output for CD ignitions. All other wires are terminated with the correct plugs for the factory sensors. There is one loose wire harness for all the optional accessories, such as fan control and AC input/output.

There are two fan outputs. Both are ground triggers for relays, allowing you to operate dual fans with separate trigger events, such as A/C and temperature controls configurable in the ECU. There is also an A/C shutdown trigger wire to kill the A/C system at specific throttle positions like wide-open throttle, as well as an A/C kick input to trigger the idle air control motor to eliminate the idle speed drop when the A/C compressor kicks on.

Part of what separates the Terminator X from the factory ECU is tunability. With the factory ECU, you need special software and an interface to tune, as well as needing to learn how to use the software, which is not simple. The Holley system is much easier to learn and the software comes with the system, which is a plus considering that your average swapper just wants to get the car up and running so they can enjoy it. The Terminator X has real-time learning, so you can literally just plug it in, load a base tune and go for a drive. There is no anti-theft to bypass or trouble codes to turn off...just fire it up and go. You don’t even need a laptop as the system comes with a 3.5” touchscreen controller that can be showcased or hidden away.

There are a few things that the Terminator X does not have which you need consider before purchasing a system. Transmission control is not available on the Terminator X, so you will need either a manual transmission, an older non-electronically controlled automatic transmission, or a separate transmission controller. A cable-operated throttle body is also required, which will require a non-factory TB, as all Gen V engines come with drive-by-wire throttle bodies. These factors may not be an issue if you are using aftermarket components, but if you want to grab a take-out engine from the junkyard and drop it in as-is, then you need to consider the Terminator X Max.

Terminator X Max

GM Gen-V LT Terminator X Max

The Terminator X is for cable-operated throttle bodies only, but the X Max can operate with drive-by wire TBs, including aftermarket and OEM units.

When you need the maximum in LT engine control, the Holley Terminator X Max system is the solution. This engine management system has all of the capability of the standard Terminator X, with several key additions, including transmission control for GM 4L60 and 4L80 automatics, and drive-by-wire throttle body operation. There are several versions of the Terminator X Max as GM has changed the protocols on their drive-by wire systems. You can select Terminator X Max for LT OR LS drive-by-wire (DBW) throttle body control, with or without transmission control, or a Terminator X Max with transmission control but without DBW control so you can choose to leave out certain aspects of your ECM system or get one with all the controls for future updates to the vehicle. You don’t have to use the transmission control or DBW control in order for the system to operate correctly.

Using the factory DBW throttle body can present some challenges, but that is mostly in the physical mounting of the throttle pedal. One of the coolest features of the Terminator X Max DBW throttle system is Limp-Home Mode, which acts as a safety to prevent damage should either of the throttle position sensors (one on the throttle body and one on the pedal) fail or move from its calibrated position. Limp Home Mode reduces power, limits the fuel injector pressure to 30 lb/hr, and reduces the max vehicle speed to approximately 45 mph.

GDI Controller


The GDI controller has built-in mounting provisions, is made from aluminum, and does most of the heavy lifting on LT-series engines. This box is included with both Terminator X and Terminator X Max ECUs and allows them to fire the big, direct injectors equipped on all LT engines.

The Terminator X and X Max systems for Gen V engines come with a separate GDI (Gasoline Direct Injection) controller. This is what powers your Gen V's GDI system. It allows you to control and tune the stock GM GDI system, including fuel pressure, injector phasing, and VVT.

DI Target Fuel Pressure

GM 10379038

The GM LTx drive-by-wire harness features a SENT (Single Edge Nibbler Transmission protocol) module. This means that the Terminator X system will plug right into GM Throttle Pedal Assembly p/n 10379038 (not included).

The fuel system for a GDI engine is a little bit different from a non-GDI, and this is because GDI requires extreme fuel pressures at the injectors. For example, the LT4 requires upwards of 2,900 PSI at max load. This is how the engine controls the placement of the fuel, the timing of the fuel, and how much fuel enters the engine. Too much or too little fuel is devastating for the internals of a GDI engine, as the fuel maps are wildly different. A GM LT-series engine air/fuel ratio can run anywhere from 10:1 all the way up to 64:1, which in any other configuration is certain death. Controlling the fuel pressure is critical for a GDI engine, and the Holley Terminator X and X Max allow you to control the pressure curve of both styles of factory mechanical pumps, which are the L83 5.3l truck - L86 6.2l truck - LT1 car pump and the LT4 car pump.

Fuel Control

GM Gen V fuel pump

On the back of the engine, under the intake, is the mechanical fuel pump. Similar to a diesel, the pump takes pressurized fuel from the lift pump in the tank and boosts the pressure to as high as 2,900 PSI. The Terminator X and Terminator X Max can control the pressure through the included tuning software.

The Gen V engine utilizes a mechanical pump, which is located on the backside of the engine, under the intake. This pump is driven off a lobe on the camshaft. It is a common practice to boost fuel pump output with a larger lobe on the cam, and some camshafts even change the shape and or quantity of the lobe(s) to boost output. With the Terminator X and X Max, you don’t need to change the lobe size, as the GDI controller can adjust for increased fuel needs without changing the lobe itself. The Holley GDI controller is designed for the stock fuel lobe, it does not support larger fuel pump cam lobe designs.

GM used 2 different styles of fuel pressure sensors on the mechanical pump, and early and a late. The early sensors, which are a 4-pin analog sensor, are used in 2014-2016 engines, while the late design, which is a 3-pin digital sensor, began being used in 2017 models. You may find a 4-pin early sensor or a 3-pin late sensor in a 2016, so you need to be sure to count the connector pins.

Injector Phasing

Essentially the timing of your fuel injectors, the injection phasing is the relationship between the injector operation and the angle of the camshaft. The Holley GDI controller can be tuned to adjust the timing of the injection cycle. Unlike carbureted or port-injected engines, a GDI engine can introduce fuel at any point into the combustion chamber, even after the intake valve is closed. This is one of the ways the Gen V engine not only saves fuel and emissions, but controls when and how power is made. “With GDI, the fuel injector is directly in the combustion chamber,” Ryan Witte of Holley Performance told us. “Which means if you spray the fuel at the wrong time you will potentially just send the fuel straight out the exhaust valve while its open and have nothing left in the chamber when the spark plug fires.” Having the ability to alter the injection of fuel into the chamber at any point gives you tons of control for performance.

The GDI controller also gives you control over the variable valve timing (VVT) system, and the way Holley has configured the Terminator X system, you have the ability to go deep or use pre-programmed settings. Witte says “Our VVT control starts with preconfigured settings as well as the GM factory VVT position tables. This eases the transition into a higher featured engine like the LTX family. Instead of being required to learn how to setup and tune your VVT parameters on top of tuning the engine as you normally would we let you to jump right into things as if it were any other engine.” The Holley system allows you to adjust the cam position table for use with VVT-compatible aftermarket cams or tuning with a factory cam, such as swapping an LT1 cam into a 5.3 L83 engine, which is a cheap upgrade.

The Terminator X and X Max control systems give you tunability beyond the factory ECU, and you get that without buying separate tuning software that is incredibly complicated to learn. LT engine swaps are very similar to LS swaps, but there are some key differences, and the Terminator X and Terminator X Max solve some of those differences, such as the fuel system. Many of the standard LT-series components are Pulse-Width Modulation (PWM) controlled. That means instead of getting on or off power to control things like the cooling fans or fuel pump, those motors are controlled by changing the frequency of the voltage instead. This is a more efficient way of controlling electric motors, but also requires more expensive components that are harder to find.

The Terminator X system eliminates the need for a PWM fuel pump, as you can use a standard return-style fuel system set to a minimum of 58psi with 255 liter per hour (LPH) flow. For stock LT engines, this fuel system is capable of supplying the engine with enough fuel to run as desired. Power adders and large camshafts may require you to up the pressure and flow rate to the GM spec of 72psi at 45 gallons per hour (GPH) to maintain adequate fuel pressure to the mechanical fuel pump on the engine.

Gen V LT Terminator X Throttle Body Plug

Holley’s harness has a small indicator module on the throttle body plug, you need to make sure this is unencumbered and protected from damage.

There is a standard 12v control wire for electric cooling fans, which are required for LT-series engines. Another common issue with LT swaps is that the factory ECU does not have a proper tach output. The only ways to get a tach signal are through the OBD-II port's reading or by adapting the cam signal to operate your tachometer, which tends to be "jumpy". The Terminator X and Terminator X Max fix all of that for a much simpler installation process.

Both Terminator systems are capable of handling additional performance enhancers for your swap, including boost and nitrous controls. Using the handheld controller, you can quickly access the boost control parameters to adjust air-fuel ratio (AFR) offset by adjusting fuel pressure, as well as adjusting timing retard per pound of boost, all without a laptop. The tuning software doesn’t stop with the basic controls either. Advanced tuners can get deep into the boost with wastegate dome pressure control, boost by time, gear, RPM, and speed, and you can incorporate boost safeties should things go awry. If nitrous is your preferred power adder, you have full control to set activation windows, timing, AFR, and even progressive curves for nitrous percentage and ignition timing, so you can maximize your nitrous injection safely within the Terminator system.

Swapping a Gen V LT-series engine is a big project, but most of it is just nuts and bolts. The hardest part has always been the wiring, tuning, and controls, but with the Terminator X and Terminator X Max, those worries are gone. Truly a plug and play system, you can have your LT wired with a base tune in a day and be ready to enjoy your new swap sooner than you think.

GM Gen-V LT Terminator X Buick

We boosted this LT1 in a 1971 Buick GS with a supercharger. Unlike the factory ECM, the Terminator system can easily handle the boost and make adjustments quickly through the handheld touchscreen controller, you don’t even need a laptop, much less a degree in computer engineering.


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