Modifying. 5.0L HO Mass Air Conversion
For Converted or Transplanted 5.0L HO Speed Density Cougars/Thunderbirds ONLY
NOTE: This section is for converted or transplanted 1987-88 HO 5.0 motors ONLY. It is not intended for the stock Cougar/Thunderbird 5.0 motor. Any attempt to convert a stock non-HO motor to mass air can result in serious damage to the engine.
T he stock '86-'88 HO engine from a Mustang has a speed-density computer setup. It's good for inferring relative air intake, but it's inflexible as far as adding high performance components, such as a healthier camshaft. The best you can do with speed density is a bigger throttle body and a K&N air filter, some exhaust work. and that's about it. Ford began using the mass air system on 5.0 Mustangs beginning in 1988 (California only), and then it was added to all V8 Mustangs from 1989-1995, as well as HO Thunderbirds/Cougars from 1991-93.
M ass air is a more accurate way to measure airflow; the net result is better response and performance. In addition, the mass air computer is a "learning" computer, which means you can add a new component, and within a minute of starting up the car, the computer will automatically recalibrate itself around that item. As far as horsepower and mass air: the wallet's the limit! But first you need to get the mass air setup in your Cougar. You can usually find the parts needed at your local salvage yard, or swap meets, or online.
You will need the following items from a 1989-1993 Mustang HO 5.0:
M ass air requires a few extra wires running from the mass air meter to the EEC-IV computer. The easiest solution for your wiring is to reuse your existing, working 5.0 harness and add a mass air adapter kit to your harness. These kits are available in the aftermarket from companies such as Interactive Systems and Technologies. Basically, it's a 4-wire hookup for the mass air sensor, and it runs from the sensor through the firewall, tapping into the main computer harness. It's very neat and efficient since you don't have to either purchase a new harness or take out your existing one. Plus, it's very inexpensive at under $50 US.
Y ou may be asking, "Why not just change out the whole harness to one used in a mass-air equipped Mustang?" The reality is that the Mustang EEC harness is not fully plug-and-play compatible with your Cougar's existing internal wiring. For example, the 1990-93 Mustang 5.0 harness is its own beast, since those were the years that the previous-generation Mustang had a driver's side airbag, and it can create difficulties when installed (such as the fuel pump not getting power). Even a 1989 Mustang HO wiring harness, which should be a little more compatible, needs several wires repinned. It's not that these harnesses cannot be used at all; it's just that they're simply not easy to use. Several people have done it, mostly for the sake of aesthetics, but it required multiple shop manuals and some time to work out issues. In this respect the 4-wire mass air add-on kit is easier, cheaper, and much more efficient.
T he mass air meter itself is coupled inside the air inlet tube, and it measures the air coming into the engine. It's the heart of the mass air operation. The sensor on top has a two-fold job: one "hot" wire inside measures air volume, while the "cool" wire measures relative air
temperature. In other words, it's a very sensitive piece and should never be touched with bare skin or any metallic objects. The sensor is calibrated to your corresponding fuel injectors. So if you're running stock HO orange 19 lb/hr injectors, the mass air sensor must match those. It is possible to remove the sensor and replace it with another sensorfor example, in the future if you're upgrading to 24 lb/hr injectors, you can keep the meter and just swap out a 24 lb/hr calibrated sensor.
T he stock Mustang mass air meter is restrictive in diameter at 60mm and has the internal air vane which restricts airflow; a different mass air meter will allow for better breathing. Most people shoot for a 70-75mm unit. Ford did make some factory mass air meters largerfor example, the supercharged V6 cars (T-Bird SC, 1989-90 XR7) had 70mm mass air meters from the factory. Swapping out the top would be an easy task. But really, if you have the cash, an aftermarket mass air meter is the way to go. They are usually much lighter, stronger, and less restrictive than a stock Ford meter.
T he mass air meter is attached to a bracket that mounts onto the passenger side strut tower; you may have to drill new holes to mount the bracket but 1986-88 cars should already have the holes. Do not attempt to use the sensor without the bracket, unless you are using a lightweight aftermarket plastic meter or a metal cold air intake system that can support the mass air meter properly (see below).
A t first, these may not seem important; with speed density, you can run around all day without the air tube on with no side effects, save for all the dirt you let in. But mass air is a closed system; if you try running without these tubes, your car won't even idle right, much less run at all. They are now two short tubes instead of your usual one. Installation is exactly how you think it ispretty simple. You will reuse your existing air cleaner box, or if you've installed a K&N Filtercharger kit, that will not be affected. If you wish to use aftermarket metal cold air intake tubes (such as those made by BBK, MAC and others), feel free to do so. They're going to give you more power due to the smooth inner walls and slight Venturi effect.
Y ou will need to replace your existing computer with the new mass air EEC-IV processor. There has been a lot of discussion on the Internet about which computer to use with which transmission. In the real world, it seems to be perfectly fine to use a manual transmission with an automatic; we've never seen any issues firsthand. However, some people say you can use either computer with a 5-speed, and not vice-versa. You will have to judge which computer will be best for you, but if you're uncertain then stick to the computer which matches your existing transmission type.
W hichever computer you decide to use, there will be a calibration code on the sticker on the outside of the grey harness connector. You will need to keep this code handy for future reference, in case you need to purchase things like a BPS or new injector.
T he following part numbers are for common Mustang mass-air EEC-IV computers with stock 19 lb/hr fuel injectors:
Automatic Cars (Calibration code A9P):