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Mass Airflow Conversion - Mass Appeal
How To Convert Your Speed Density Mustang To Mass Airflow.
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.
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.
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.
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.