In 1986, Ford replaced the tried and true four-barrel carburetion setup with a sequential multiple-port fuel injection system. This new EFI-equipped 302 scared the heck out of many Mustang enthusiasts, but offered improved driveability, fuel mileage, and smooth performance. And while Ford hadn't quite worked the bugs out for hot rodders wanting to bolt on intake manifolds, heads, and some lumpy cams, the future would eventually be bright for EFI.
After some searching, I came...
After some searching, I came across Fiveology Racing (fiveologyracing.com). I spoke with Brian Bastob about the MAF conversion and ultimately my near future plans for the GT. Fiveology offers three conversion kits for varying performance needs, and Brian can put together a MAF conversion kit tailored specifically for the 5.0 Mustang. I also upgraded to a 70mm throttle body and EGR spacer, so Brian set me up accordingly. The kit is complete with everything you'll need minus the throttle body and EGR spacer. Brian is also knowledgeable about this conversion and was helpful with our tech questions.
Any radical modifications made to the speed density engine causes the said system to go "full tilt" (in pinball or poker terms) because the load/fuel mixture tables are inflexibly burned into the processor. If you exceed these parameters by installing a cam that's too big, or an induction that flows too much, then the system can no longer effectively compute injector pulse width (fuel/air ratio) and timing. The net result is a loss of driveability, an overly rich condition, or in extreme cases, engine failure due to detonation caused by lean mixtures and/or over-advanced timing.
Like most 5.0L fanatics, your author just can't leave it stock. I already have a pretty wicked '85 Mustang LX Coupe getting ready to be reassembled and I bought this particular '88 GT to be used as a daily driver. A promise to my wife to leave it stock turned into "it's just a couple of modifications, honey..." Married guys with Mustangs, you know the look that follows!
I knew that my '88 GT was a speed density car when I bought it, but now that I've started modifying it, I can't stop. I also know that before you can add any real performance modifications beyond cold-air intakes, gears, and exhaust on a '86-'88 speed-density-equipped 5.0L Mustang, you have to convert to mass airflow.
So here we are doing a mass air conversion on my Mustang. But first let's take a look at the difference between speed density and mass airflow.
Here is the engine in speed...
Here is the engine in speed density form.
Speed Density vs. Mass AirFlow
With a speed density system, actual intake manifold pressure is now measured using a manifold absolute pressure (MAP) sensor, as well as inlet air temperature (IAT), and in addition to the previously sensed TPS and engine rpm. Now the ECU fuel control programming includes a desired air/fuel ratio table, the injector flow rates, engine cubic inch displacement, a volumetric efficiency table, and the programs necessary to instantaneously calculate inlet airflow, required fuel flow (for the desired A/F ratio found in the A/F ratio table), and finally the correct injector pulse width.
Once the MAF is installed,...
Once the MAF is installed, you can see a clear difference in the inlet tract.
With mass airflow, the air entering the engine is actually measured using a mass airflow (MAF) sensor. Injector pulse width is still calculated in the same manner as shown previously, however, now the airflow is actually measured instead of calculated. In a sense, things happen before the fact, rather than after the fact. The big advantage of a MAF system is that you can change things on the engine that affect airflow and maintain driveability. In most cases, the MAF sensor will realize the change in airflow, and the fueling will still be correct. It makes the MAF system the most forgiving for engine modifications.
The first thing I did before buying any parts for my conversion was to do research. I decided I didn't want to waste time trying to scrounge parts from various salvage yards and hope I had everything I needed to complete my conversion.
'86-'88 Mass Air Conversion Installation
Once I had all my parts together, I drove the Mustang to Scatts Automotive, where John Scatterday performed most of the mass airflow conversion. We decided to disassemble the mechanical components before getting started on the wiring harness and EEC.
If you decide to use your stock throttle body, EGR spacer, and injectors, you can skip right over this section and move on to the mass airflow sensor wiring harness installation. Make certain to disconnect your battery first.
 First we disconnected the...  First we disconnected the battery, then moved over to the other side of the engine compartment and removed the air box cover, clamps, and air intake hose. |  Next we removed the breather...  Next we removed the breather hose from the throttle body and the two coolant hoses that are connected to the EGR spacer. We unplugged the wiring from the idle air control valve and removed the throttle position sensor from the throttle body. Once this was done, we removed the two bolts holding the throttle cable bracket in place and were able to pop the throttle cable off of the ball mount. Then we unplugged the wire harness from the EGR valve. |  Four bolts hold down the throttle...  Four bolts hold down the throttle body and EGR spacer. Once we removed those, the throttle body and EGR spacer came right off. We turned the upper manifold's six bolts counterclockwise and removed it to access the fuel rails and injectors. |
 We unplugged the harness to...  We unplugged the harness to the injectors carefully and removed the two bolts holding the fuel rails. Once that was done, we carefully pulled out the stock 19-pound injectors. (Be sure the engine is cool because some fuel will leak/spray out.) Check for errant O-rings that may have come off the injectors and stayed in the fuel rail or injector ports in the intake manifold. Now the 24-lb/hr injectors can be installed, but before doing that, we applied a small amount of pre-assembly lube around the O-rings on both ends of the injectors. The injectors were then carefully pressed into the intake manifold ports. |  The fuel rail is pressed down...  The fuel rail is pressed down on top of all four injectors simultaneously until you feel them all "pop" into place. Finally, we replaced the two bolts that secure the fuel rail to the intake manifold. We repeated these steps for the other side. |  Working with the upper intake...  Working with the upper intake manifold, we removed the vacuum hose that is routed from the bottom of the upper intake manifold to the MAP sensor located on the firewall. Next, we capped off the vacuum port on the bottom of the upper intake manifold to prevent vacuum leaks. We left the MAP sensor port open to the atmosphere. |