Electronic Fuel Injection, MAF and MAP Sensors - EFI Basics Tech

Air density is impacted by air temperature. The Air Temperature Sensor is the MAF's sidekick, offering further insight into the quality of the air coming into the engine. The MAF does most of the work and the air temperature sensor provides fine tuning data.

A Coolant Temperature Sensor plays a key roll in engine start up and the engine's performance before it reaches its optimum operating temperature. It mostly controls the amount of fuel used during and after start-up.

The Atmospheric Pressure Sensor is basically an onboard barometer informing the ECU of its elevation. This data is used as part of the air density equation and allows the engine to run more efficiently in a place that's much higher up above sea level, like Denver, Colorado.

A Tach Sending Sensor taps into the voltage coming of the coil. The pulses are converted to illustrate the engine speed in the ECU. Engine speed is a key element in every calculation the ECU makes.

Mass Air vs. Speed Density
Both systems do the same thing but go about their missions in a different way. A mass air set-up is much more agile than a speed density system in that it meters the air via the Mass Air Flow sensor (MAF), and, using input from the sensors at its disposal, makes tuning adjustments in open loop operation based on the input it receives. At WOT, the system goes into closed loop operation and makes its decisions with fewer sensor inputs. The mass air system uses an algorithm to devise its tuning changes so it can compensate for most power adders.

Conversely, a speed density system plots its air/fuel ratio and ignition curves on pre-conceived maps. It doesn't not meter air but uses a Manifold Absolute Pressure sensor (MAP) to compensate for altitude and ambient air temperature that the ECU uses to calculate air mass. Rather than plotting its tune in open loop, a speed-density ECU takes in its sensor signals and selects a pre-programmed map. For instance, at WOT it employs Map 53, then it sees some changes and moves to Map 27 and so on. The shortcoming of the speed density approach is its inherent inability to react to changes in airflow/volumetric efficiency of the engine brought about by some more aggressive power adders' forced induction for sure, but a battery of hard hitting bolt-ons can jump beyond the speed density system's ability to compensate. To accommodate said power adders, the computer will need to be diligently reprogrammed and in boosted situations, positive air pressure conditions will need to be addressed.

Some popular speed density applications include '92-'95 Civics, Chevy LT1s and other Tuned Port Injection creations from GM. The mass air camp is represented by the classic Nissan Sentra SE-Rs, '90 and up Z-Cars, Toyota 2JZ Supras, Evos and WRXs.

Whether its mass air or speed density if you are planning to modify the engine by way of forced induction, a competent understanding of the sensor array and inner workings of an EFI system will certainly prove beneficial. When the time comes to select a tuning scheme for you, new combination, you and your performance shop will be speaking the same language.