James Lawrence
April 1, 1999
Contributers: James Lawrence

Step By Step

View Photo Gallery
Don't get overwhelmed when you pop the top of the Accel box and a maze of wires and sensors comes falling out. Clockwise from the Accel decal is the Variable Injector Controller (VIC), injector harness, VIC box power harness, main DFI harness, 83-lb/hr injectors, and the Accel main processor (center).
This is a closeup of the optional VIC. It provides for individual cylinder control by allowing fuel-trim and injector-timing changes at each individual cylinder. The VIC acts as a driver for each injector instead of a driver for every two injectors in the basic DFI scheme. This is important when running low impedance injectors like ours.
This is the collection of sensors supplied with the DFI kit. They include a three-wire oxygen sensor, air temperature sensor (ATS), coolant temperature sensor (CTS), manifold absolute pressure (MAP) sensor, idle air control (IAC) module with harness, and the DFI harness interface modulator.
If you want to retain your stock wiring harness, DFI can accommodate this with its custom jumper board. While we opted for a complete replacement of the harness to simplify things, Summers recommends this setup for those people who may sell their car sometime in the future. This way, if you sell the car, you can keep your DFI setup for the next project without having to do a major operation.
Summers begins by pulling the stock wiring harness from the engine compartment, removing the upper intake, and pulling the injector harness. Don't cut this stuff--it's worth money to someone. This step really cleans up the engine compartment and removes weight at the same time.
The big 83-lb/hr injectors get installed and the fuel rails get replaced. Connect the Accel injector harness into position.
Summers then installs the ATS in place of the stock sensor.
Summers mounts the CTS in the front driver's side of the GT-40 lower. This is actually a GM sensor that will help with the refinement of warm-up and enrichment adjustments.
For reference, the VIC is connected to the DFI injector harness (already laid into engine compartment). The VIC will eventually be installed in the interior out of the way of radio frequency interference from the ignition system (and prying eyes).
The upper intake gets reinstalled and Summers puts the IAC into position with the supplied adapter plate. Ford's two-position sensor gets replaced with a GM unit that allows more precise control of engine idle and stepped pulse of the injectors.
Summers reuses a couple of empty holes on the firewall for a nice mounting spot for the MAP. A one-bar MAP is used for naturally aspirated, a two-bar MAP for boost levels of up to 17 psi, and a three-bar map sensor if you want to really put some air through the motor. Take a guess which one we used?
Summers starts running the DFI main harness with its multiple connections through the firewall, where it will connect to the ACCEL processor in the interior.
The ACCEL ECM finds a home In the footwell, replacing the stock EEC IV in the kick panel. All connections are made directly to the processor.
We'll be back with a follow up story on how to tune one of these things after we get to the track and do some real-world testing. For now, Summers wouldn't let us within 20 feet of the computer screen. You know how tuners get about their secrets.

There's a certain mystique surrounding Accel's Digital Fuel Injection (DFI) system. When first introduced in the '80s, only the really high-tech racers with money to burn dared try a stand-alone fuel injection system. Without solid tuning experience, it was easier to do more harm than good with the system. After all, the DFI takes the tuning away from the conventional fuel pressure regulator and timing light and puts it in the hands of whomever is at the laptop. But, as time wore on and more and more racers demonstrated the benefits of this incredible tuning aid, it became a viable alternative for those who are ready to take their 5.0 Mustang to the next level.

When we first considered the buildup of a serious supercharged 5.0 (See sidebar "Project Mondo Stocker Setup"), we knew that we would eventually be talking about an aftermarket engine control system. For the money, the DFI system is a great choice for those who want anything more exciting than a hot street car. If you want to go into the 10s or faster with a blown and injected 5.0, you are going to need a host of aftermarket components, including a race fuel management unit ($300), boost timing retard($300), an accurate mass air sensor like a Pro-M 83mm unit ($400), some sort of device to control the air/fuel ratio--like the FMS Extender ($500), Anderson PMS ($750), or C&M Software-programmed chip ($200)--and perhaps some sort of secondary injector system ($350) to help control injector pulse-width with low-impedance injectors over 50 lb/hr. These last devices are also necessary if you want to operate the motor past the factory dictated 6,250 rpm limit. As you can tell, these are pricey items that can quickly shoot a hole in even a serious player's budget. But, with the DFI, you get a system that replaces all of the above mentioned parts and provides an infinite number of adjustments for tuning and expandability. Also, by making the MAS unnecessary, you effectively remove one of the major restrictions from the intake tract.

The benefits of the DFI are well documented. With a factory computer, Ford had to make several potential owners happy. As hard as it is for us to believe, there are some people who actually buy a 5.0 Mustang with no intention of making it faster. That forced Ford to design an ignition and fuel plan that would make a Mustang work in less than tuned-to-perfection condition. Also, production variances make it nearly impossible to optimize a computer setup for every car. Besides that, Ford designed a computer program that had to take into account that the motor might not be fed high-octane gas at every fill up or have a brand new set of ignition components every 1,000 miles. Basically, the EEC IV has to guess what the right strategy is to make the motor work to its fullest potential. And, it does a great job, but the DFI can do it better.

When a 5.0 gearhead replaces the factory stuff with the DFI package, the tune can be custom-designed to that specific motor, for that one purpose. And, in our case, that purpose is maximizing the horsepower and torque that reach the pavement by way of 28x10.5 Mickeys.

You're probably wondering why we haven't included all of those groovy screen shots that have become considered mandatory with tech features on the DFI. There are two reasons. First, the programming wasn't done on our 5.0 at the time the installation story shown here was shot because we are constantly adding more parts to the project. This time we told Jim Summers to install it with the GT-40, but while we were at ASSC, Mike Hally at Hi-Flow Heads was whittling away on a truck lower to mate with a box upper we had acquired. So, as soon as the hand grenade--uh, motor--is reassembled, we'll be back with an in-depth feature on just the programming aspects of the DFI. Second, we have heard horror stories about readers putting Grand National programs on a nitrous-assisted 5.0 just because they saw the maps in a magazine, and tossed the cookies of an otherwise-nice piece. It is one of those things that can really get you in trouble, and we're not going to put our readers in jeopardy.

To get you started, most dealers will provide a base program preinstalled on the processor (it comes from ACCEL with no programming). If not, whatever shop you choose for a final program should be able to send you something they call a limp program just to make the car run without getting into trouble. This will allow you to get the car to the shop for final tuning.

As we've talked to more and more users of DFI, we've become believers in both the quality of the product and the skills of the tuners who use it. As their experience continues to grow with the more common 5.0 Mustang combinations, DFI becomes a more viable choice for those who thought that it was once an option for only the elite.

For these reasons, we had noted DFI expert, Jim Summers of ASSC, install a complete DFI system with the optional injector driver on Project Mondo Stocker. In the experienced hands of the ASSC staff, the installation went smoothly and took about three hours to get the harness and all sensors installed. Finishing touches and programming will take a little bit longer.