When we first developed the Retro 5.0 project, one of the topics for discussion was how we were going to control the engine on the dyno. The core engine came complete with most of the factory sensors in place (who knows if they were operational, though) and a factory wiring harness. This led to the discussion of potentially using an original computer to control the build. That was a possibility, since your author is an admitted hoarder, and an original A9P EEC-IV ECU happens to be sitting on the shelf.

While the EEC-IV was a capable unit in its day, anyone who has worked with those ECUs knows the frustrations that can arise compared to working with a modern ECU or even an aftermarket standalone ECU. So after some deliberation (mainly about introducing an anachronism into the project), we all concluded that it was acceptable to use modern engine controls from the start. And, really, there was only one option on anyone’s minds — The Holley Terminator X.

Terminator X Plug-And-Play EFI For The Small-Block Ford

One thing that the modern age has offered in the world of aftermarket standalone ECUs — besides wildly advanced computing power — is plug-and-play capability. Full standalone ECU systems used to require a full-on rewire to terminate the ECU’s harness in the proper connections. While not an insurmountable hurdle, it is definitely a task we wanted to avoid if at all possible. We’re familiar with (and fans of) the Terminator X’s LS plug-and-play variants, so when Holley announced the plug-and-play application for the 1987-’93 Ford 5.0L engine, our hearts leaped.

While Holley has a Ford MPFI kit as a single part number, they also have all the pieces for a plug-and-play late-model 5.0L engine setup available as separate components, which is the route we went to ensure as much of a seamless integration as possible. So, let’s walk through each component of the system, and explain it.

The heart of the system: The Terminator X ECU. Equipped with an impressively powerful suite of features and hardware, the compact unit also has features like an onboard diagnostic system to show any errors that might arise. The recently updated software has added a lot of additional functionality to the unit, as if there wasn’t enough already.

The heart of any Terminator X system is, of course, the Terminator X ECU itself. The ECU is common among all of the different kits, be they for GM, Ford, Mopar, or whatever the application might be. The system has become wildly popular thanks to its incredible capabilities and budget price. Besides the large variety of tuning tables for hugely granular control of the system, Holley’s built-in self-learning features help prevent you from going down the wrong path. To that end, the system also comes with a base map for the engine, so that you have a decent starting point and aren’t having to scratch-build a base map.

One of the features that really appealed to us, is the built-in 1-bar MAP sensor. This eliminates the mass airflow meter from the circuit. Having grown up in the world of MAFS tuning, both in Fox Body and other Blue-Oval applications, this is a headache we weren’t looking forward to as the project progressed. The system also incorporates a Bosch LSU 4.9 wideband oxygen sensor, which absolutely aids in tuning.

Future Proofing With Terminator X

While it might have been kind of cool for nostalgia’s sake to try and run the project engine on the old EEC-IV computer, we would have outgrown that quick, fast, and in a hurry with what we have planned. As we’ve discussed previously, the engine will be getting a Vortech supercharger once all the naturally aspirated testing is done, because, well, that is exactly what would have happened back in the 1990s.

Also like the ‘90s. we’ll be introducing a little bit of the giggle gas before it’s supercharged. An incredibly common choice for an extra kick in the pants during the late-model Mustang era, we’re going to be incredibly safe with the nitrous, thanks to the Terminator X’s built-in nitrous control. It can handle a single stage of nitrous in either a wet configuration (where the nitrous system handles the injection of additional fuel) or a dry configuration (where the ECU commands additional fuel from the fuel injectors).

The Holley engine harness is clearly labeled and designed to not only be easily integrated with the 5.0L Windsor platform, but also offer expandability beyond just the factory connections.

Additionally, the Terminator X offers a simple on/off control, or full progressive control of the nitrous, allowing for the power to be ramped in via pulsing the solenoid(s). The ECU also has the ability to target a specific closed-loop AFR, as well as incorporating rich and lean safeties to keep you from turning your pistons into a liquid.

The boost control offered by the system once we install the blower will be incredibly useful as well. While we will have to wire in an external MAP sensor, the harness is pre-wired for it. With the latest update to the Terminator software, the amount of control that can be exerted on the boost curve based on a huge number of parameters is incredible. While those are usually associated with turbochargers, there have been some interesting ideas explored lately, on controlling supercharged boost with methods other than impeller drive speed. We might play with some of that if we have extra time on the dyno. At least we know we have a capable ECU to play with.

Harnessing The Power Of Plug-And-Play

Where the real beauty of the plug-and-play-ness (I think we just made up a new word) comes from is the main harness (P/N: 558-128). It’s designed to integrate all of the components and controls found in fuel-injected “late-model” pushrod powerplants from the Blue Oval — specifically, the 5.0L and 5.8L Windsor engines. The beauty of offering the main harness separately is that you aren’t limited to just a Terminator X ECU. The 558-128 harness will also work with HP and Dominator ECUs from Holley EFI. So, if you need more or fewer features, you can still plug-and-play with a late-model powerplant.

While our injector harness is designed to be a plug-and-play piece with factory-style injectors, having the standard Holley injector harness connector (lower-left corner) will allow an easy change to any injector connector type. Holley offers injector harnesses for a large variety of injector types, to suit anything we swap out to in the future.

Besides being terminated for all of the traditional sensors seen in an EFI system, the harness comes with an idle air control motor connector designed specifically for Ford’s pulse-width modulated IACs. Additionally, the harness allows for either aftermarket Dual Sync or Hyperspark distributors to be used (if that’s your jam), or, the factory TFI-style distributor setup can be utilized by simply connecting a TFI ignition harness (P/N: 558-305). Boom, factory-style distributor and ignition control.

While the plug-and-play aspect infers that we want to use OEM-style 5.0L fuel injectors, there are a multitude of options available that will interface with the main harness’s injector harness connector. For us, we opted for P/N: 558-209 which ties the factory 5.0L injectors into the system. While it might seem weird that the Terminator X kit isn’t a single part number, by designing modularity into the kit, Holley has ensured that you get everything you need and nothing that you don’t.

This little harness allows the factory-style Ford TFI ignition to be used. If you wanted to run a dual-sync or Hyperspark distributor, the harness has provisions for that. However, we are running a drop-in replacement 5.0L distributor and coil, so with this adapter, the TFI module plugs right in.

Sensing Changes

As we mentioned earlier in the article, the core engine’s sensors were suspect. Let’s just say that gas station sushi sounds like a better choice than trying to reuse any of the OEM sensors. So, we did what we have done time and time again when replacing factory sensors, we jumped onto RockAuto.com. Having replaced every sensor in the engine bay of our ’94 Mustang GT previously, we only had to slightly alter our parts list to accommodate the differences between an ’87-’93 5.0L and a ’94-’95 5.0L.

One of the main features of the plug-and-play 5.0L Windsor harness is a provision for the pulse-width modulated idle air control valve. The harness is wired and terminated for the factory-style plug, meaning no aftermarket replacements needed. We replaced the original unit with a factory-replacement part from Rock Auto.

Because the Holley EFI harness is terminated for certain Holley sensors and certain OEM sensors, we erred on the side of caution and ordered all new factory sensors. For the top end, we ordered a new IAC motor and a new throttle position sensor (before we realized that the BBK throttle body is equipped with a new one out of the box), while being able to forgo a new MAF sensor, since we’re now running on speed-density. We’ll need to repin the TPS pigtail to fit the Holley harness’s weatherpack connector, but the parts are supplied with the kit.

Then, we added a factory coolant temperature sensor and intake air temperature sensor, along with a new oil pressure sensor (which we need to discuss in a little more detail, later). We plugged off the factory oil level sensor port in the oil pan, because, well, we didn’t need it. We ordered a pair of new oxygen sensors, as well as a PCV filter, valve, and grommet for the intake tract. Literally every factory sensor we needed, and then some, for under $150. Then, for good measure, we added a new Motorcraft starter to the cart.

Here you can see the factory coolant temperature sensor in a water passage on the intake manifold (on the left, along with the factory intake air temperature in the number five cylinder runner (on the right). Both of the sensors were quite inexpensive to replace. Since we ordered them before we decided to run the Terminator X from the start, it’s no biggie to swap them out for the Holley versions.

Some of the factory replacement sensors we ordered (before we made the decision to not use the EEC-IV at all in the project) need to be replaced by Holley sensors for the Terminator X. On the dyno, we’ll swap the factory intake air temperature sensor for the Holley 534-20 air temperature sensor, and the factory coolant temp sensor for Holley’s 534-10 coolant temperature sensor. We’ll also swap one of the OEM narrowband oxygen sensors for a Holley 554-155 Terminator X-specific wideband oxygen sensor. These are calibrated at Holly, to ensure the self-correcting and learning features of the ECU work perfectly.

Now, back to the oil pressure sensor. The factory unit varies the resistance in the ground circuit to give a really rough estimate of pressure to the gauge cluster. Definitely not the high-resolution pressure sensor we’re used to working with when datalogging. So, like every enthusiast ever, who wants to plumb in a more accurate oil pressure gauge, we’re going to have to replace the factory sending unit with a Holley oil pressure transducer (P/N: 554-102) to get an accurate oil pressure reading in the Terminator X, as well as plumbing in a fuel pressure transducer (P/N 554-102). Notice the part numbers — that’s one of the nice things about the Holley ecosystem; a 0-100psi pressure sensor is a 0-100psi pressure sensor.

Now, it’s just a matter of plugging in all the harness connectors on the dyno, loading in the base map, and getting our baseline numbers on this combination. Luckily, the system will grow and adapt with us throughout the testing process soon to come. And we know that all of the results will be consistent, since we won’t be switching horses midstream, like we would be if we tried to use the original EEV-IV A9P computer to start. So make sure to stay tuned, as it’s time to make some noise with this engine.