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.
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.
