Home: Mustang Tech: Maintenance and Tune Up: EFI tuning part 2: sensors
EFI tuning part 2: sensors


Well, in part 1 we skipped one of the MOST IMPORTANT aspects of a complete tune up.

Your EEC relies on a number of sensors to gather information about several stuff such as Oxygen content in the exhaust, coolant and air temperatures, throttle position, etc.

This information is used by the EEC (PCM) to tune the delivery of fuel, air and spark.

If any of those sensors fail for any reason, the EEC will instead relay on stored values in its memory to compensate for the loss of a sensor signal. This will trigger a FAULT CODE which will be displayed as a "check engine light" and a stored fault code number inside the EEC memory.

Sensors can fail for a number of reasons: faulty connection, dirt in sensor or an actual hard fault (dead sensor). But in reality, the chances of a complete sensor failure are small, most of the time the failure is either a dirty connector, bad wiring or dirt in the sensor.


Check PART 1 Sensors

MAS Sensor (Mass Air Sensor) also known as MAF or MAM

The MAF is one of the most important sensors in your engine, it is composed by 2 elements, the housing and the meter. The housing is a 3"+ aluminum cylindrical element that sits inside the air filter housing. On top of the housing sits the meter, it is a small black box that contains 2 thin heated wires (when on). Those wires change their resistance as air flow cools them down and the resulting voltage is sent to the EEC to tell it how much air is flowing, the EEC then will adjust injector pulse to change fuel delivery.

One of the most common MAF failures is caused by DIRT that passed through the air filter. If you use a stock air filter, the time it would take for the sensor wires to gather enough dust to fail would be long. But in the case of aftermarket OILED filters such as a K&N it will take a short time if the filter is over-oiled.

So if you have a K&N that has been cleaned and re-oiled, let it sit for a while to let the excess oil drip, then clean it with a lint free cloth.

A contaminated Maf sensor can be diagnosed by several symptoms:

  • LEAN CONDITION, displayed as KOER codes from the O2 sensors
  • Backed-up timing, a result of the lean condition in which the EEC will back timing to reduce chance of detonation
  • Low TOP END power, as a result of reduced timing and fuel.

So what can you do to remedy this?

The answer is simple, remove the MAF housing from the air box. At the top of it remove the 2 retaining tamper proof Torx Bit screws and GENTLY pull the sensor out. If the 2 filaments of the sensor are dirty (dark in color) clean them with a Qtip until all contaminants are removed. Check the Maf wiring harness for loose or dirty connectors and bad wiring.

Reinstall and test your car.

You will instantly feel a GREAT difference in horsepower, probably as much as 30hp are lost when the MAF fails by contamination.

O2 HEGO sensors (heated oxygen sensors)

This is another very important sensor, as it "reads" the amount of oxygen that's present in the exhaust. This information is sent to the EEC which then compensates the fuel accordingly.

SN95 oxygen sensors are "pre heated" which means they will reach operating temperature faster than non heated ones which reduces emissions on engine start.

Again, the most common cause of failure in an O2 sensor is contaminants, which are always present in the exhaust as carbon and probably unburned oil.

The chances of O2 sensor hard failure are larger as the car gets older but in most cases they last lots of years, and with some precautions you can make them last a lot longer.

A bad 02 sensor will show several symptoms:

  • Rich or Lean fuel condition
  • O2 sensor fault codes 136, 137, 139, 144 and 171 through 178
  • Reduced HP

5.0 engines have 2 heated sensors close the heater pre-cat, on 3.8 and 4.6 models there are 4 sensors located before and after the catalytic converters.

To check the sensors first disconnect and inspect the wiring, remove the sensors and clean them, don't use any type of chemicals to do this, the cleaning should be done by using a PROPANE TORCH, place the sensor tip inside the propane flame for a few seconds at a time until all contaminants get evaporated by the heat. Place the sensors back in place.

Engine Coolant Temperature sensor (ECT)

The ECT sensor is a thermistor, basically a resistor that changes voltage accordingly to temperature changes. It provides a reading that's used by the EEC to change fuel delivery at engine startup to reduce emissions and monitors the temperature of the engine.

Codes 116 to 118 indicate an ECT sensor problem or failure.

Remove the ECT sensor, on 5.0 engines it is located at the front passenger side of the lower intake manifold, on 4.6 engines it is located at the left side of the alternator outside the engine block.

If you see some rust in it clean it by sanding the surface using a fine grit sandpaper, Also check the connector and wiring. Reinstall and check for codes, if some are present change the unit.

Intake Air charge temperature sensor (ACT or IAT)

Also a thermistor the IAT sensor changes voltage accordingly to ambient air temperature, the EEC uses this information mostly to change fuel delivery when the engine is cold at startup. The sensor is located inside the Intake air duct.

Codes 112 to 114 will set a IAT sensor code in the EEC, remove and inspect the sensor it could get contaminated by engine oil , K&N oil or dust. Clean the sensor with isopropyl alcohol. If the sensor still fails replace the unit.

Throttle position Sensor (TPS)

The TPS is located at the end of the throttle shaft on the throttle body. Using the TPS voltage signal the EEC determines fuel delivery based on throttle position. A bad TPS can be the cause of bad idle, which is caused by the injector pulse fluctuating. Some loss in performance can also be expected.

Codes 122 through 125 are present when the EEC detects a TPS problem.

Sensor Safe carb cleaner or TB cleaner can be used to clean the sensor. If the problem persist replace it.


Enjoy your stang and drive safely

Article by: GTRaptor Profile | E-Mail

Sensors are the heart of any EFI engine, get to know the basic maintenance procedures.

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