The cast-aluminum 76mm C&L design is unique in that calibration changes are affected by changing an aluminum sample tube inside the unit (The user supplies his own sensor element) By changing the diameter of the trailing portion of the sample tube, flow over the sensor element can be altered for compatibility with different-size injectors.

Fooling the system?
Whenever an engine is fitted with larger fuel injectors a corresponding change must be made in the calibration of the mass air sensor. Otherwise the sensor will send a voltage signal to the PCM corresponding to the 19lb injectors (or whatever you were running), resulting in a rich condition.

Manufacturers of mass air meters use two methods to modify the calibration, and it is the difference in these two methods that results in people taking sides with one manufacturer or another.

The calibration can be changed in two ways, by modifying the electronics in the sensor itself, or by changing the speed and amount of air passed over the sensor wires. Companies like Pro-M (Best Products) modify the sensor, while C&L uses the latter method. The goal is the same, to make the computer think there is less air than there really is, thus reducing the amount of time the injector is opened. Why do we want that? Because we have upgraded to a larger injector, and thus it needs a shorter pulse-width than a smaller injector. Either way the end effect is that the EEC system is "fooled" because the change made is simply to reduce the signal being sent to the computer, rather than modifying the actual tables in the EEC which are created for a 19lb injector (24lb for a 1993 Cobra processor.) There is actually a third, more correct way, by modifying the "lookup" tables in the EEC itself. However this would require a EEC Tuner or similar software, and is out of the scope of the majority of enthusiasts.

Pre 1989 Mustangs (and other Ford Mass Air cars) used a square mass air connector.

Post 1989 used this oval connector.

So is there a advantage or disadvantage to how the mass air meter is calibrated for larger injectors? Well the answer depends on which camp you are in. In terms of cost, we like the C&L sample tube method, because if you ever upgrade injectors size in the future, all you need is a $20 sample tube. With the other method you must send the entire mass air meter back to the manufacturer for a recalibration. Some think this is preferable since you get a "more accurate" calibration...however the C&L devotees will tell you this offers more chance of error and problems, since each unit is individually calibrated, rather than produced the under high-tolerance and consistency of CNC machining.

We found one other reason why we liked the C&L method. We noticed both our test cars had different shaped sensor connectors. The '88 has a rectangular connector, while the '92 has an oval connector. Because the C&L requires you to use your existing sensor, the different connectors does not a problem. However with the other mass air meters on the market owners of 1988 and possibly 1989 5.0L with the square connector would be required to upgrade the harness and connector to the later oval style.

C&L 76mm mass air meter and TrueFlow intake tube installed. Note the meter is slightly rotated. We found that "clocking" the meter resulted in a slightly smoother idle with our non-stock cam.

Modified 1988 Mustang
The engine in our '88 LX Mustang was recently rebuilt (see Build a 5.0L articles). Rather than a stock rebuild, we upgraded the induction with a set of Edelbrock RPM heads, RPM intake, and a mild Lunati camshaft (215/222 .522 lift). We also had a 65mm FMS throttle body installed from the get-go.

We initially set the engine up with the stock 19lb injectors and 55mm mass air meter. We knew this would not supply sufficient fuel for the better breathing engine, but we figured it would make for an interesting test to baseline the car with the stock injectors/mass air and then upgrade to 24lb injectors and matching mass air meter. Note that it is really impossible to run anything other than 19lb injectors with the stock mass air meter. There are companies that will recalibrate the stock meter, but it doesn't make sense to do so, especially when you can get a new and larger meter for around $200.

Injector Installation

We removed the upper intake and replaced the stock 19 lb/hr injectors with FMS 24 LB/hr fuel injectors. Be sure to de-pressurize the fuel rail using the schrader valve before removing the injectors, otherwise you'll get fuel spraying out and on to a potentially hot engine or headers!

There is really no point in installing higher flow fuel injectors without replacing the stock fuel pressure regulator with an adjustable unit, such as the BBK piece shown here. The adjustability (using the allen head screw) allows fuel pressure to be raised or lowered.

Finally we adjusted fuel pressure at idle to 36 psi with the vacuum line disconnected from the regulator. Track testing at lower and higher fuel pressure showed the best results at 38 psi.

As stated earlier in the article, whenever you upgrade injector sizes you must make a corresponding change in the mass air sensor calibration. This is either done by modifying the sensor housing, or modifying how much air passes through the sample tube, as is the case with the C&L meters. We simply ordered up the C&L with both 19lb and 24lb samples tubes.

With the 19lb injectors (set at stock 39-40psi fuel pressure) and stock 55mm mass air meter, the car ran a best of 13.46 @ 103.7 mph. It definitely seemed to be lacking top end "pull", which we attributed to the engine running lean with the 19lb injectors.

Unlike with the '92, we were not able to complete the testing for the '88 during one track session, since we had to remove the upper intake to change injectors. So we took the car back to the shop and returned the following week with the injectors, fuel pressure regulator and new 76mm mass air in place (see "Installation" side bar.")

With the C&L 76mm system, and 24 LB injectors at 38psi, the car immediately felt stronger, especially mid-top end. We had to play with fuel pressure a little bit at the track, but finally with 38 psi in the stock fuel rails, we ran a respectable 13.29 @ 105.

In the case of a mildly modified 5.0L, it is clear that the stepping up to the larger injectors and better flowing mass air meter yields impressive benefits. Obviously the gains here are due largely to the increased fuel, but there is no denying the larger mass air meter and tube add measureable power.

Sources:
207G Green Cove Rd.
Huntsville, Alabama 35803
(256) 882-6813
www.cnlperformance.com