Mark Houlahan
Tech Editor, Mustang Monthly
September 19, 2018

When factory electronic fuel injection (EFI) first hit the Mustang in the 1980s, many enthusiasts felt it would be the death knell for performance. Little did any of us know at that time that there was really nothing to worry about, and that we’d have Mustangs today rolling off the assembly line in excess of 400 horsepower (and more for specialty models like the supercharged Shelby GT500s from 2007-2013). Sure there were some problems early on as owners and the performance aftermarket figured out these OE systems and how to get the most out of them, and the same can be said for aftermarket bolt-on EFI solutions.

Over the years, the options to convert your carbureted engine to EFI have been many. From using the intake, injectors, wiring, and sensors from the ’87-’93 Fox Mustang to early throttle-body injection (TBI) units based off of GM truck units, there always seemed to be teething problems and a learning curve. However, over the last five years or so the bolt-on EFI game has really entered the next chapter, if you will, allowing anyone with basic mechanical abilities to be able to enjoy the benefits of modern fuel injection on their classic Mustang.

The aftermarket systems have matured with well-designed aluminum throttle bodies that directly and easily replace your 4150/4160 flange carburetor (if you’re using a stock Ford Autolite 2100/4100 carb and manifold we suggest upgrading to an aluminum intake with your EFI swap) and easy-to-integrate wiring with often less than six wires to connect! Meanwhile, the most important advancements have been wideband oxygen sensor integration and onboard tuning (either via a wired touchscreen or a Bluetooth connection to a small tablet).

The wideband sensor allows for “self-tuning” functionality, taking a lot of the guess work and frustration out of tuning the system, especially for your typical street engine combination. Originally a sensor found only on high-end exotic cars and in expensive race-oriented EFI systems, wideband sensors are now used in most OE applications, including the current-generation Mustang. Couple that fast-acting input with some basic parameters set up during the initial power-up of the system, and most cars run great right out of the box. More radical camshafts, power-adders, and other upgrades will often require a bit more hands-on tuning; it’s just the nature of the beast.

The Holley Sniper EFI system is a complete bolt-on EFI solution. All you have to do is supply an EFI-capable fuel system, which Holley can help you with as well. Included in the Sniper 4150 Self-Tuning EFI kit is its cast throttle body (available in black, gold, or polished finishes), wideband O2 sensor, handheld touchscreen controller, and all necessary wiring—PN 550-511 is shown.

Over the last 10 years or so we’ve installed all manner of EFI conversion systems, several of them from Holley and its sister brands. Watching the progression of these systems has been nothing short of amazing, and that goes for supporting products like fuel system plumbing, fuel pumps, and the like. Gone are the days of poking your fingers with braided stainless fuel hose and trying to find a spot to mount a fuel pump low enough on a framerail to actually receive fuel from the tank. Today we have push-on hose and fittings that are simple to route and terminate and drop-in fuel tanks with EFI pumps in them. All of this makes for an easier installation and user experience.

Today we’re upgrading a friend’s 1968 Mustang hardtop with Holley’s latest, its Sniper EFI system. The Sniper system features a cast throttle body with integrated ECU, four 100 lb/hr injectors, OEM-style throttle position sensor, idle air control solenoid, and fuel pressure regulator. Simply bolt it down in place of where your carburetor used to reside on your manifold and half the job is already done! No external ECU box or fuel pressure regulator to mount. The base kit also features a pre-terminated wiring harness with just four basic connections to make (battery positive and negative, ignition switch, and rpm) and a genuine Bosch wideband oxygen sensor for fuel-map learning with a trick no-weld oxygen sensor mounting solution as well. Lastly, Holley adds a user-friendly touchscreen interface with an easy-to-understand “wizard” interface, yet the system can be custom-tuned via laptop and a CAN/USB adapter if preferred. The system has built-in timing control if so desired, can control cooling fans, and has additional output options while offering users data logging capabilities as well. All this in a system starting at just under a thousand dollars!

Jumping right in on this ’68 Mustang hardtop we disconnected the battery and pulled the Holley four-barrel the owner was using.
The Holley Sniper throttle body is a direct replacement and slips right over the studs. A new base gasket is installed (not included) here as well. Holley offers a nifty installation kit option under PN 520-1. The kit features base gasket, mounting studs/nuts, air cleaner stud, wiring terminals, and more to make your installation a breeze. Note that if you’re using the popular Lokar billet pedal and throttle cable conversion that you’ll need to update your cable mounting bracket to something that is compatible with the Holley Street Demon carburetor linkage, which is what the Sniper linkage is modeled after.
One of the critical components of the Sniper install is the coolant temp sensor. It has to be in a port that sees constant coolant flow—meaning it has to be “behind” the thermostat. Since this older Weiand manifold only had one port, we transferred the sending unit for the dash gauge to the thermostat housing and installed the Sniper sensor in the intake.
The 3.5-inch color LCD is a single wiring connector to the throttle body. We passed it through one of the old heater hose openings in the firewall, as the holes were no longer used with the aftermarket A/C system the owner installed. Be sure to use grommets for any wiring passing through sheetmetal.
The main wiring harness for the Sniper is fairly simple, with most wiring pre-terminated. There are only four wires to connect—power, ground, switched ignition, and fuel pump. Here we’ve mounted the system’s sole relay and fuse holder to the firewall with the thought being the air cleaner will hide most of the “EFI bits” to maintain a retro carb’d look. The blue wire you see coming off the harness is the fuel pump power lead.
The fuel pump wire was passed through the firewall (we used an existing hole and added a small grommet to the opening using a Holley-brand Mr. Gasket grommet kit PN 3706) and routed to the rear of the car, as we’ll be utilizing one of Holley’s new Sniper EFI fuel tanks with internal fuel pump.
Power and ground connections go directly to the battery, per the Sniper instructions, so that’s a no-brainer. However, the switched 12V source (pink wire) could be a cause for some head-scratching. We’re connecting it to the switched ignition wire that would normally go to the coil. However, we’re ONLY doing that because we’ve previously bypassed the resistance wire between the ignition switch and the firewall bulkhead connector for an aftermarket ignition that was installed a couple of years ago. So whatever you do, ensure the wire has full battery voltage in both START and RUN positions of the ignition switch. The red wire seen here is the switched power feed for the ignition (more on that in the next few photos).
While not necessary for the Sniper install, we opted to upgrade the Mustang’s ignition system at the same time. The Mustang did have an under-cap electronic ignition system, but otherwise the rest of the system was stock (coil, wires, and plugs). We’re using Holley’s MSD-brand Pro-Billet distributor (PN 8479), Blaster 2 coil (PN 82023), cut-to-fit Street Fire 8mm wires (PN 5550), and new 6EFI ignition system.
The MSD distributor and coil are direct replacements for the stock pieces, so we’ll focus on the new 6EFI ignition control. Wiring is simple with power and ground directly to the battery, coil positive and negative, and the magnetic pickup wiring plug to the distributor. Switched power wire was tied into the EFI wiring (see caption 8) and the unit was mounted to the front of the passenger shock tower.
We prefer cut-to-fit wire sets versus pre-terminated wires, as you have the freedom to route and mount them where you see fit without any excessive wire length to deal with. It’s a little extra effort to measure, cut, and crimp, but the end results are well worth it. You can see our MSD Blaster 2 coil is in place here as well.
With the main EFI system parts installed and wired and our ignition upgrades handled, it’s time to tackle the fuel system updates. Holley offers a universal fuel pump that can mount in the top of your existing tank, but the stock tank on this ’68 was pretty beat up, so we opted for a drop-in Sniper EFI tank. Thankfully the stock tank has a drain plug for easy removal of the fuel.
Just a few self-tapping bolts and a couple of nut/bolt assemblies in the corner, and disconnection of the filler neck tube, and the tank is out.
Our new Sniper EFI direct-fit fuel injection tank, PN 19-102, comes in a ready-to-assemble kit, including the tank, fuel pump, and fuel level sending unit along with a new filler neck hose.
Following the included instructions and diagram we took measurements of the tank depth and determined the length of the fuel pump assembly and return hose off of that depth measurement.
Our assembled EFI pump ready to install. The Holley Sniper EFI tank kit’s fuel pump is rated at 255 lph, which is good for up to 550 hp naturally aspirated.
The kit includes a sending unit, and while universal in nature, it has the correct resistance to work with the OE fuel gauge in the dash. In a nutshell, the unit needs to be shortened to the length you see here to properly fit in the tank.
The new Sniper EFI fuel tank with fuel pump, sending unit, and filler neck bung installed is ready for installation into our ’68 Mustang. The powdercoated finish means the tank will look good for a long time to come.
Wiring the in-tank fuel pump is easy. Simply connect the blue fuel pump feed routed earlier to the “+” terminal on the fuel pump. We used the remaining extra wire to run the ground for the sending unit and fuel pump to one of the tank mounting bolts. The original gauge sender wire was removed from the grommet in the trunk floor and connected to the new sending unit in the top of the tank, and the grommet was sealed with silicone. We’ve also installed a pair of Earl’s AN-6 NPT adapters, PN AT981606ERL, into the pump supply and return fittings.
The original mechanical fuel pump mounted on the timing cover, as well as all of the old fuel hard lines, were removed from the Mustang to clean things up. A fuel pump block-off plate will be required for the timing cover (not included). We forgot to order one from Holley/Mr. Gasket, so we picked a Ford Performance plate up locally.
To plumb our new EFI fuel system we ordered 30 feet of Earl’s Vapor Guard fuel injection hose in 3/8-inch ID, PN 750066ERL (Earl’s is a Holley brand). This hose is multilayer with a barrier, compatible with all commonly used fuels (pump gas, E85, alcohol, race gas, etc.), and virtually eliminates the common fuel vapor smell of many aftermarket fuel hoses.
Earl’s Vapor Guard hose, be it EFI or carburetor spec, requires the use of Vapor Guard hose ends. These hose ends are available in popular AN sizing and configurations like straight, 45-, and 90-degree ends. The fittings can be clocked to suit hose routing and are secured by Vapor Guard hose clamps.
Earl’s offers several Vapor Guard hose clamp configurations, including single and dual crimp, and traditional screw clamps, all rated for EFI use. We opted for the permanence of crimp clamps and ordered the single crimp style, PN 750010ERL, as we were familiar with them and have the proper tool in our toolbox already. If you don’t have the correct tool, the screw-type clamps are easy to secure and are reusable.
We began our hose routing with the return line (note there is an S for supply and an R for return on the pump fittings). The hoses will need to pass through the trunk floor somewhere to be routed under the car. We’ve used the forward left corner on previous builds with grommets from our aforementioned Mr. Gasket grommet kit.
We routed the EFI return line as high as we could along the rear framerail and into the transmission tunnel to keep the lines away from hot exhaust parts and to protect it from any potential road debris that may come along. Rubber-cushioned P-clamps, sourced locally, with self-tapping hex-head screws secured the lines. Here the return line is secured to the Sniper return line fitting using a 45-degree Vapor Guard fitting.
For the supply line we started at the throttle body with another 45-degree fitting and ran it parallel to the return line using the same style of clamp under the existing screws we previously installed. Since this Mustang was using a bullet-style glasspack muffler we had plenty of room under the rear seat to mount a Holley EFI 10-micron fuel filter, PN 162-550, which requires two 3/8-inch NPT to -6 AN adapters (AT981666ERL) to allow connection to the Vapor Guard AN fittings.
The supply line was completed with a length of Vapor guard from the fuel filter to the fitting on the fuel pump in the tank and the lines secured with tie-wraps.
Depending upon the air cleaner housing you are using you might have interference with the supply/return lines/fittings at the Sniper throttle body, but don’t worry because Holley has your back with this nifty 14-inch air cleaner drop base with reliefs for the Sniper fuel line areas (PN 120-510). Slip this over the throttle-body flange and use your existing air cleaner and lid without issue.
With our new drop base installed, the owner’s original Holley air cleaner fit up just fine. We also added a little underhood “pop” with a set of Holley’s Sniper EFI–branded valve covers in black, PN 890011B.
Our last installation step is getting the wideband O2 fitted. Due to the aforementioned glasspack muffler’s mounting location we had to use the long-tube header collector for the sensor location. Here we’ve drilled the properly sized hole to accept the O2 sensor mounting kit.
The kit-supplied O2 sensor mounting bung includes a high-temp gasket and two stainless band clamps for mid-pipe installation aft of the header collector. If you need to install directly into the collector, as we are here, you’ll need to order the larger 3-inch kit, PN 71014301-RHKR. Be sure to secure the O2 sensor wiring away from the exhaust. We used the transmission dipstick tube as a secure way to route the wiring back to the EFI unit.
All that’s left after getting everything buttoned up is to reconnect the battery, check all wiring connections are secure and away from heat or moving parts, and turn the key to “on” to boot up the EFI’s computer so that you can input your engine’s specs into the Sniper EFI handheld’s wizard tool. Basic questions like number of cylinders, displacement, cam type, ignition type, and more are just simple questions to answer, and once the base calibration is uploaded, you can start the engine and get it warmed up to set your hot idle speed. It’s that easy!

Check 1, 2–Check 1, 2

If you’re at all familiar with the late-’80s to early-’90s Mustang EFI systems, you’ll know that Ford provided a small check valve you could screw a fuel pressure gauge to in order to verify fuel rail pressure. When upgrading to an aftermarket EFI solution, generally it is common practice to install a fuel pressure gauge in the external fuel pressure regulator so you can set your fuel pressure manually on the regulator. With these throttle body–based systems like the Holley Sniper setup you see here, the fuel pressure regulator is built into the unit and is pre-set from the factory, so why would you need a fuel pressure gauge? Right off the top of our head, the quick answer is to verify fuel pressure from your fuel pump, but it can also be used as a diagnostic tool to show a weak pump, restricted filter, damaged/crushed fuel line, etc. Earl’s offers liquid-filled fuel gauges in both carbureted and EFI ranges (we grabbed the 0-100 EFI, PN 100187ERL) and this nifty AN -6 gauge adapter, PN AT100199ERL. Using the gauge adapter we can easily install the pressure gauge inline between the supply line and the throttle body for initial startup and testing, and then remove it and store it in our toolbox for future projects or EFI system diagnostics.