How to Upgrade your Outdated ECU to Modern EFI

10 min read

How to Upgrade your Outdated ECU to Modern EFI

10 min read

Barn finds are the hot topic right now and on the engine side of things, we could use that same concept for resurrecting older EFI systems that have been sidelined in a barn or parts shelf because they are electronically ancient. Late ‘80s OE and some aftermarket multi-point fuel injection systems actually performed fairly well in their day but the software and electronics are now horribly outdated. With regard to automotive electronics, nothing ages faster than digital control strategies.

There are probably thousands of small-block Chevys running wild on the streets right now with an antiquated factory TPI system ECU. We’re talking computers with removable chips! An equally large number of small- and big-block engines are likely limping around on outdated and inefficient aftermarket fuel injection systems just begging for a more efficient way to manage spark and fuel.

One answer is Holley’s Terminator X. This system was initially designed as an aftermarket, plug-in replacement controller for GM LS engine swappers. The idea was to create a powerful ECU that was easy to use and had self-learning capability that offered modern tuning advantages. The LS Terminator X was so successful that soon other engine platforms were clamoring for a little love.

We are one of those builders with a ‘90s era TPI-style small-block Chevy. The original ECU still controls spark and fuel but time and technological advances in computing power have relegated our ‘90s control unit into something of an electronic knuckle dragger. The engine in question is 357ci small-block with good heads and an aggressive hydraulic roller valvetrain that was still clinging to an ancient aftermarket EFI system. The control portion of this system was so aged that our laptop could no longer communicate with the software. It was time for a change.

Another potential candidate could be GM’s RamJet crate engines that for years have been commanded by a rudimentary, non-feedback Mercury Marine MEFI 3 and later MEFI 4 ECU. These are password protected EFI controllers that are not user-accessible and have a habit of running quite rich at part throttle. There are tuners who, for a fee, can unlock and tune these systems but frankly the Terminator X is a far better solution.

We decided it was time to introduce our Marconi electronics to the Ethernet. All we had to do was unplug that fossilized EFI from the engine and plug in the Terminator X.

Our particular engine was running an old but still quite useful SuperRam intake manifold originally designed by the late John Lingenfelter. The manifold is a five-piece design that requires some effort to assemble. The plenum and both runners have to be removed in order to access the injector harness, so while we were elbow-deep in the bowels of this manifold, we added a set of 48 lb-hr Holley injectors to ensure we had plenty of fuel flow just in case we decided to experiment with dry flow nitrous or perhaps a mild centrifugal supercharger. The SuperRam is more than capable of serious airflow and the injectors are good for more than 700 normally aspirated horsepower.

Ignition control is also part of the Terminator X system and we wanted to fully take advantage of that control. We chose a new MSD small-cap HEI style distributor since it was originally intended to be used in this same application, but there are several other options that are listed in the accompanying Ignition Options sidebar.

One point to note with the Terminator X package is that the Holley harness is intended to be used with late model GM sensors. Some of these have carried over from the older applications but the idle air control motor (IAC), the throttle position sensor (TPS), and manifold air temperature (MAT) sensor connections have been updated.

This required cutting the wires and adding the WeatherPak style pins to be used with the matching connectors. For the TPS, any standard male 3-pin Weatherpak connector will suffice. We’ve also included an illustration for re-pinning the IAC. For the MAT sensor, we just ordered a new sensor from Holley that plugged right in. The part numbers for the connectors and the MAT sensor are in the Parts List.

While we intend to use a Tremec TKX manual five-speed behind our small-block, other options include late model electronic overdrive automatic transmissions such as the 4L60E or 4L80E. Holley anticipated this demand and offers a Terminator X MAX ECU package that includes a very comprehensive transmission controller and wiring harness that is integrated into the Terminator ECU.

Another Terminator X software option is nitrous control. This can be either a single shot or progressive control system and can be integrated as either a wet or dry nitrous application. As an example, with our 48 lb-hr injectors and an engine that can make approximately 500 normally aspirated horsepower, we could add an additional 200 horsepower of dry nitrous and supply the additional fuel required through the injectors. Or, if your injectors were smaller, you could convert to wet nitrous where the additional fuel would be added at the plate behind the throttle body. We’ve tried both combinations with a SuperRam manifold with great success although the dry nitrous offers more accurate control over fuel distribution.

With our engine out of the car and the SuperRam manifold reassembled, we thought we’d fire it up on our engine test stand to ensure that all was right with the world. With a high pressure fuel delivery system and 12-volt power, we began the Terminator X configuration process by choosing the Wizard icon from the main menu. There are just a few inputs required to tell the Terminator X ECU the basic information it needs. With accurate input, the software then creates base fuel and spark maps from the inputs that will allow the engine to start and run.

Using the setup Wizard we ran through a series of inputs including multipoint (MPFI) for a V8 with the correct firing order (1-8-4-3-6-5-7-2 for a small-block Chevy), displacement of 357ci, a target idle speed of 850 rpm, and our cam specs. Terminator X outlines three cam categories: #1 (below 235 degrees of duration), #2 (235 to 260 degrees), and #3 (above 260 degrees). Our cam fell right in the middle of category 2 with 242 degrees of duration at 0.050 so we chose category #2. All of these specs refer to intake lobe duration at 0.050-inch tappet lift.

Among the other inputs is the injector size. There are several specific injectors listed in the Terminator software so we chose to upgrade our injectors to a set of Holley 48 lb-hr units that the software accommodates. If your injectors are not listed in the Wizard, you can enter them as “other” in the Terminator X software. This requires investing in a Holley “dongle” cable that will connect the Terminator X ECU to a USB port in your laptop. Using the free Holley Terminator X software, that is very similar to the Holley HP and Dominator versions, the laptop access will then allow you to customize your software to include your specific injectors.

TermX SBC EFI Software

If you desire to go a little deeper into tuning, Holley offers an adapter that connects the Terminator X to your laptop. With Holley’s free software, this offers the ability to make minor trim changes that are not possible with the hand-held. For inveterate tuners like us who love to experiment with minor trim changes, this is something we had to have.

To do this, you will need to access the Engine Parameters portion of the software found under the little picture of the ECU in the upper left hand corner. Clicking on Engine Parameters will take you to Fuel Injectors where there is a long list of injectors that the system recognizes. If your injector is not listed, you will need specific injector off time data for your injectors in order for the Terminator X to accurately control the injector.

With all the input data loaded into the Terminator X and with fuel pressure and ignition power, we discovered our fuel pressure regulator had failed and needed replacing. Once that was accomplished, the engine immediately started and quickly settled into the prescribed idle speed. One item that is important to note is that the Terminator X system will not start self-learning until the coolant temperature reaches 160 degrees. Once warm up is achieved, the system learns very quickly.

TermX SBC Other Kits

You can make the move to a Terminator X MAX kit that adds a transmission controller that will manage either a GM 4L60E or 4L80E electronic overdrive transmission. There are also Ford, Mopar Gen III Hemi, and LS Terminator X MAX kits beyond just the universal kit for the small- and big-block Chevys.

With the ability of the self-learning software to quickly adapt idle, part throttle, and WOT air-fuel ratios to the engine, it doesn’t take long for the software to create an accurate fuel curve. The spark tables may take a little custom tuning on your part but this is still much simpler than juggling initial, mechanical, and vacuum advance curves to achieve the proper timing. There is no self-learning for spark control.

This is a little bit like upgrading an older car with modern electronics that will improve just about every part of its performance curve. The best part is that the Terminator X and Terminator X MAX are both very affordable. That’s one advantage of 21st Century electronics – you end up with a better running engine without having spending a ton of money. That’s one of the advantages of car building in the 21st Century.

TermX SBC first fire

With the Terminator X inputs complete on our small-block, we set fuel pressure at 43 psi, hit the starter, and within a few seconds our small-block was idling comfortably. Remember that the system cannot begin to learn until coolant temp reaches 160 degrees F. A finalized tune will require installing this engine in the car to finalize all the load areas on the fuel map.

Diagnostic LEDs

LED #FunctionColorDescription
1HeartbeatGreen/FlashingECU is powered
2Engine RunningGreen
Engine Running
Engine Not Running
Too hot/cold, not calibrated
Normal function
Sensor replacement required
Sensor is heating
Sensor failed
4TPS CalibratedGreen
Not Calibrated
6Crank SensorGreen/Blue
Below crank-to-run RPM
Crank error detected
7Camshaft SensorGreen/Blue
Below crank-to-run RPM
Cam error detected

Other Terminator X Ignition Options

  1. No Terminator X Ignition Control - run a universal MSD HEI or MSD Ready-to-Run distributor with mechanical and vacuum advance
  2. MSD 8366 Pro Billet distributor with MSD CD ignition box. This will require harness 538-304. This same harness is used to run inductive ignition through the distributor with full spark control.
  3. Terminator X ignition control with a locked-out MSD distributor. This will require a CD box, such as an MSD 6.

Parts List

DescriptionPart Number
Holley Terminator X Universal MPFI Kit 550-936
Bosch/EV1 Style High-Impedance Fuel Injectors, Set Of Eight522-488
GM Late Model HEI V8 External Coil Distributor 8366
HEI GM Small Cap Ignition Harness558-304
Digital Dash Input/Output Adapter With Unterminated Vehicle Harness558-433
3-Pin Weathertight Connector (single)8172
Idle Air Control 4-square Weatherpack Connector570-214
Air Temperature Sensor534-20
MSD Super Conductor Spark Plug Wire Set, Multi-Angle Plug, HEI Cap, Red31189

Optional Components

Terminator X Max Universal MPFI Kit with Transmission Control550-942
MSD Digital 6A Ignition Control6201
Holley EFI Dual Sync SBC/BBC Distributor565-200


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