If you own an '84-'09 Mustang, chances are beyond good that it has electronic fuel injection. Since the introduction of Sequential Electronic Fuel Injection (SEFI) in 1986, fuel-injection has been fitted across the board on Mustangs, both base models and V-8. Prior to '86, the only fuel-injected Mustangs were the limited-production SVO and GT Turbo models with port fuel injection and the 5.0L models with Automatic Overdrive, which had Central Fuel Injection (CFI) with two throttle-body injectors.
Fuel injectors are fired in...
Fuel injectors are fired in time with the engine's firing order. Each injector sprays fuel as the intake valve for that cylinder opens.
Beginning in 1986, the Mustang GT had SEFI with eight 19-lb/hr fuel injectors and return-style fuel injection. In 1999, Ford went to a no-return fuel injection system with fewer parts and less hassle. Fuel injection requires virtually no maintenance regardless of all those TV commercials pushing cleaners; the rotating valve pistons are self-cleaning during the injection process. Unless gum accumulates on the spray head to disturb the spray fan pattern or an O-ring develops a leak, fuel injectors don't need maintenance. And, for the most part, they require replacement only when they fail or when performance becomes erratic.
Fuel injectors are electromagnet (solenoid) operated valves located in each intake port that open when triggered by the engine's computer. They operate in time with the engine's firing order as each intake valve opens. If your Mustang has Central Fuel Injection, the two injectors operate in a buzzing, pulsing fashion in synch with throttle position and engine speed. As the throttle is opened and more fuel is required, injectors are operated for longer intervals, yielding more fuel above the throttle plates.
Here are the two basic types...
Here are the two basic types of fuel injectors you can expect to see. At left is the EV14 pencil injector with USCAR two-pin plug. At right is the fat-body EV1 injector with a Jetronic/Minitimer two-pin plug. The EV14 looks similar to an EV6.
What size and type of fuel injector does your Mustang need? The answer depends on the model year, engine type, and performance demeanor. If you have a hopped-up 5.0L or 4.6L, you're going to need a higher-flow-rate fuel injector to keep up with a hotter cam, larger heads, and free-flow exhaust. If you have a showroom stocker, you're going to need exactly what your engine came with-19-lb/hr injectors, which are a butterscotch color. Injector flow rate is identifiable by color.
Fuel Injector Types
There are three basic types of fuel injectors you can expect to see on '84-'09 Mustangs:EV1: This is the more traditional fat-body Bosch fuel injector used from '84 to '98 on 2.3L turbo fours, 5.0L High Output, and 4.6L SOHC/DOHC V-8s. It uses a two-pin Jetronic/Minitimer plug where the two pins are flat, not round.
These are EV1 injectors for...
These are EV1 injectors for older fuel-injected Mustangs. On top is a 19 lb/hr injector for 5.0L High Output and 4.6L SOHC engines. Below is a 22-lb/hr MSD injector. Flow rate is identifiable by injector color. Where it gets tricky is fuel rail fit. Not all aftermarket injectors will fit your Mustang's fuel rail because the length isn't always exact.
EV6: Narrow, pencil-body Bosch injector used on non-return fuel injection systems from '99-up. Uses USCAR two-pin plug with round pins.
EV14: Also a Bosch piece, which looks similar to the EV6 injector and uses the EV6's USCAR two-pin plug. It differs from the EV6 in how it attaches to the fuel rail. The injector head is also more pronounced.
The Bosch EV1 injector was introduced in the '67 Volkswagon Type 3 as the first electronic fuel injection system. This is the fat injector we see on '84-'98 5.0L and 4.6L engines as well as the 2.3L Turbo Four.
In 1992, Bosch introduced the EV6, which is thin like a pencil with the USCAR two-pin plug. Mustangs didn't get this injector until '99. The improved Bosch EV14 injector showed up in 2001. What makes the EV14 better than the EV6 are nice refinements that improve performance and reliability: improved spray pattern; a single molded body that will not leak; and fewer parts. The EV14 is interchangeable with the EV6. In fact, it is also interchangeable with the original EV1 if you use the Ford Racing M-14464-A8 USCAR/Jetronic adapter kit.
See your Ford Racing Performance Parts catalog/website for the right type of injector for your application.
 From left to right are an...  From left to right are an EV6 and two EV14 injectors. The EV6 and EV14 look a lot alike. Look for a jackleg plug connection with the EV14. The EV6 plug is more unified into the injector body. |  Fuel injectors are sold as...  Fuel injectors are sold as sets or individually. The price depends on injector type, ranging from $35 each to over $100 each. |  This is the Ford Racing M-14464-A8...  This is the Ford Racing M-14464-A8 EV1 to EV6/EV14 adapter kit available from Mustangs Plus. There's also the M-14464-U2J kit to adapt EV6/EV14 to EV1. |