Engine Performance - RayTek AUTOPRO Manual De Instrucciones

Engine Performance

Engine Misfire Trouble
Shooting – Gasoline
A gasoline engine may idle rough or have an
intermittent misfire. Lack of fuel, lack of spark or
lack of cylinder pressure (compression) can cause
misfires. In a gasoline engine, any of these three
problems means no combustion in that cylinder.
No heat coming from the exhaust port will indicate
lack of combustion. A lean fuel condition will
cause a higher combustion temperature. Individual
exhaust temperature will be easier to obtain on
vehicles equipped with separate exhaust pipes for
each port. On exhaust manifolds, heat transfer will
occur and make it difficult to identify changes in
temperature between ports. The best results on a
manifold will be observed when the vehicle is first
started and the engine is cold. On newer vehicles,
if a cylinder is not operating effectively, the check
engine light may turn on and a Diagnostic Trouble
Code (DTC) will be set.
To locate a misfiring cylinder using the IR
thermometer, start engine and allow the idle to
stabilize. Measure temperature at each exhaust
port, noting changes in temperature. See Fig. 5. If
any cylinders show a significantly lower tempera-
ture than other cylinders, check that cylinder for
the following:
n Malfunctioning ignition supply to affected
cylinder.
n Malfunctioning fuel supply to affected cylinder
(rich condition).
n Excessively low cylinder pressure
(compression).
If any cylinders show a significantly higher
temperature than other cylinders, check for a
fuel restriction to affected cylinder causing a lean
misfire. Most likely cause is a dirty fuel injector or
vacuum leak.
If any cylinders indicate a noticeable, but not sig-
nificantly lower or higher temperature than other
cylinders, this could be an indication of poor cyl-
inder performance. This check may warn of other
mechanical problems. Check for the following:
n Worn spark plugs or wires.
n Malfunctioning fuel supply to affected cylinder
(rich/lean condition).
n Low cylinder pressure (compression).
n Carbon buildup.
Fig. 5: Measuring Exhaust Port
Temperatures
Engine Misfire Trouble
Shooting – Diesel
A diesel engine may be hard to start, lack power
or idle rough in all climates and at all operating
temperatures. The engine may have a cylinder that
is misfiring.
To locate a misfiring cylinder using the IR
thermometer, start engine and run until engine
reaches normal operating temperature. Run
engine at a fast idle and measure temperature at
each exhaust port, noting changes in temperature.
See Fig. 5. A weak cylinder can be identified as
having a temperature less than surrounding cylin-
ders of 55°C (100°F) or more. If a weak cylinder is
found, check that cylinder for the following:
n Malfunctioning fuel injectors or fuel injector
pump.
n Excessively low cylinder pressure
(compression).
Engine Temperature Sensors
Emission controls on most computer-controlled
vehicles rely on many sensor inputs, allowing
proper control of spark and fuel supply in all
climate and driving conditions. Engine Coolant
Temperature (ECT) sensor and Intake Air Tem-
perature (IAT) sensor (if equipped) inputs can be
verified using the IR thermometer. To