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How To Set Up A Terminator X EFI System To Run Nitrous On A Foxbody Mustang

By: Wes Duenkel | 03/26/2021 < Back to Motor Life Home
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Nitrous is the easiest way to add horsepower, and Holley's Terminator X EFI system makes it even easier. Holley's Terminator X simplifies running nitrous by incorporating features that normally would require add-on devices that increase complexity and cost. The Terminator X software eliminates the need for these by incorporating a TPS switch, RPM window switch, progressive controller, and delay switch into the software. All these features are just a few clicks away with Terminator X. One simple accessory makes it possible: the Holley High Current Nitrous Solenoid Driver (p/n 554-111).


(Check out this post if you missed how we installed a Terminator X EFI system on this 1991 Mustang GT.)


For this project, we're using a basic "dry" nitrous setup from NOS that includes a 10-lb bottle, a NOS Pro-Shot nitrous solenoid, and jets for up to a 150-horsepower gain.


The factory 5.0L intake manifold is a cast-aluminum labyrinth which suffers from enough distribution problems of its own without asking it to flow fuel properly. With this in mind, the best nitrous systems for 5.0L Fox Mustangs are either "wet" plates that fit between the upper and lower intake manifolds, or a "dry" setup that injects nitrous in the intake tube and uses the fuel injectors to add the necessary fuel.


Speaking of injectors: we upgraded the stock 19 lb/hr fuel injectors with some 36 lb/hr units from Holley (p/n 522-368). To keep the injectors well-fed, we replaced the factory in-tank fuel pump with a Holley 190 LPH in-tank pump (p/n 12-901).


Check out the following details on how easy it is to add nitrous when using the Holley Terminator X EFI system!


Fox nitrous kit

Here's what we used to spray our Terminator X equipped '91 Fox Body: A basic dry nitrous kit from NOS served as the basis of our setup including a 10-lb nitrous bottle, Pro-Shot nitrous solenoid, and a range of NOS precision stainless steel jets.


Fox Nitrous 554-111

The relay and activation switches were replaced with the Holley High Current Solenoid Driver (p/n 554-111).


Fox Nitrous no relays

You'll note there are no other switches, relays, controllers in our parts layout. The Terminator X EFI system plus the Solenoid Driver does it all!


Fox Nitrous dry setup for Terminator X

When running a "dry" nitrous setup with the Holley Terminator X, additional fuel when on nitrous is injected through the existing fuel system. To meet the fuel needs of a 150-hp shot, we replaced the factory 19-lb/hr fuel injectors with these Holley 36-lb/hr injectors (p/n 522-368) and a Holley 190 lph in-tank pump (p/n 12-901).


Fox Nitrous Holley 190LPH fuel pump

The Holley 190 LPH pump is a direct replacement for the factory pump. We dropped the fuel tank, disassembled the module, and replaced the factory pump with the higher-output Holley pump


Fox Nitrous Fuel Pump Module Reassembled

With the fuel pump module reassembled, we fished it back into the tank and secured it with a fresh gasket and retaining ring.


Fox Nitrous new fuel harness

Old fuel pump harnesses can be trouble--especially with a fuel pump that draws more current like the Holley 190 LPH. To make sure our Fox didn't strand us on the side of the road, we replaced the old pump harness with this fresh one.


Fox Nitrous upper manifold removal

Next, we removed the upper intake manifold so we could swap the injectors. With experience, it's pretty straightforward and only takes a few minutes.


Fox Nitrous injector replacement

We pulled the factory injectors, lubricated the O-rings of the Holley 36-pound units, and installed them in the factory fuel rails.


Fox Nitrous dry nozzle

The dry nitrous nozzle goes into the intake tube, so we used a drill and the supplied tap to install it. We marked the outlet of the nozzle so we knew it was pointed in the right direction after installation.


Fox Nitrous electrical schematic

The electrical side of this install is extremely simple. Just a few wires is all it took to get our Holley Terminator X EFI system controlling nitrous.


Fox Nitrous Terminator X harness modification

The Holley Terminator X harness has an input/output connector conveniently located behind the kick panel. We pulled the blank connector and installed the harness Holley supplies with the Terminator X. We used two wires on the harness: the white with red wire to arm the nitrous, and the gray with red wire to trigger the nitrous solenoid.


Fox Nitrous arming switch

The White with red wire went to the arming switch which we hooked up to a switched 12-volt source.


Fox Nitrous wiring solenoid

The gray with red wire went to the yellow wire on the solenoid driver harness. Here's where it comes out of the firewall and goes to the solenoid driver which we mounted nearby.


Fox Nitrous power to solenoid

Next, we connected the orange wire from the solenoid driver harness to the battery. We used the fuse holder from the NOS relay harness and ran the orange wire along the firewall to the solenoid driver.


Fox Nitrous blue wire

The blue wire from the driver harness went to the nitrous solenoid, with the remaining solenoid wire leading to ground. We also connected the included stainless steel nitrous hose to the nozzle in the air intake tube and installed the nitrous jet.


Fox Nitrous spark plugs

To reduce the risk of detonation, we swapped in spark plugs (Motorcraft ASF22C) that were two heat ranges colder than stock. This might be overkill, but we wanted to be on the safe side.


Fox Nitrous bottle mounting

We finished up the nitrous system installation by running the nitrous feed line from the solenoid to the bottle which we mounted in the trunk.


Fox Nitrous Terminator X pin mapping

The Terminator X software is where the magic happens. Before setting up the nitrous delivery options, we needed to tell the Terminator X how we wired up the arming switch and the solenoid which wires to use via the pin map.


Fox Nitrous Terminator X Nitrous adjustments

This is where make adjustments to our nitrous delivery. Everything including TPS triggers, RPM and air/fuel activation windows, delays, and timing controls are available. We can even cut nitrous off once boost comes in from a blower or turbo! Cool, right? But, there's more. The wideband oxygen sensor adds closed loop control to nitrous, so you can simply run a target air/fuel ratio when on nitrous just like you would naturally aspirated. Drag racers will appreciate the progressive control feature. You can ramp nitrous in over time or over RPM to soften the nitrous hit and maintain traction. Our dry nitrous setup allows us to ramp in additional fuel to accompany the nitrous. With all these options, we're ready to hit the spray with confidence!


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