Chapter A: General Diagnosis
20
actuator control solenoid. Exhaust camshaft timing
is fixed.
• A single timing chain drives both exhaust camshafts
and both intake camshaft hydraulic actuators. While
valve overlap is variable, valve lift and duration are
fixed.
• Cam timing is determined by the ECM using the
crankshaft position (CKP) sensor and camshaft po-
sition sensor (CMP 1 and CMP 2) signals. At idle,
the intake camshafts are fully retarded and valve
overlap is zero degrees. At higher speeds and
loads, the intake camshafts can be advanced up to
40 crankshaft degrees.
•Each intake camshaft has a separate camshaft po-
sition sensor, hydraulic actuator and control sole-
noid. If little or no oil pressure is received by a hy-
draulic actuator (typically at engine startup, at idle
speed or during a fault condition), it is designed to
mechanically default to the fully retarded position
(zero valve overlap) and is held in that position by a
spring loaded locking pin.
COOLING SYSTEM SERVICE
An engine that runs too hot or too cold has poor perfor-
mance, reduced fuel economy, and increased emission
levels. Engine temperatures that are too low or too high
are often the result of a cooling system problem. How-
ever, other problems, such as incorrect ignition timing,
overloading the engine, long periods of idling or slow-
speed operation, and other factors, can cause over-
heating as well.
Check the coolant level and test the concentration using
a hydrometer. Look for signs of oil and combustion con-
tamination. Engine oil escaping into the coolant will not
mix. The oil will float on top of the coolant. Combustion
gases will chemically react with coolant to rapidly break
it down turning it a rust-brown color. The presence of
combustion gases can not be visually verified. Check
using a chemical test kit or exhaust gas analyzer; see
Book A1 "Engine Repair" of this series.
Cooling System Inspection
Use a pyrometer to monitor actual engine temperature
and eliminate the possibility of a faulty gauge, warning
lamp, sending unit, or circuitry. Once the problem is ver-
ified, inspect the cooling system and make the neces-
sary repairs.
Approach diagnosing an overheating problem by first
determining when and at what interval the problem oc-
curs. If the owner adds water, find out how much and
how often. Secondly, determine whether the problem
can be isolated to a specific driving condition. Visually
inspect all cooling system hoses and replace any that
are worn or damaged. Also, inspect the water pump
drive belt for wear, damage, and correct tension and re-
place or adjust as needed.
Cooling System Testing
Testing of the cooling system generally consists of test-
ing the coolant and performing system and radiator cap
pressure tests. If the system and cap both hold pres-
sure, test the operation of the thermostat.
Testing the Coolant
Coolant concentration and effectiveness are tested with
a refractometer or cooling system hydrometer, figure
1-23. For accurate results, the coolant should be hot
when tested. Before testing, draw a coolant sample into
the hydrometer and return it to the radiator several times
to stabilize the internal thermometer of the hydrometer.
Test as follows:
1. Hold the hydrometer straight and draw enough
coolant to raise the float. The float should not touch
the sides of the hydrometer.
2. With the hydrometer at eye level, take a reading by
noting the top of the letter on the float that is
touched by the coolant.
3. Find this letter on the hydrometer scale; read down
the column under the letter until you are opposite
the thermometer reading.
4. The number shown at this point is the degree of
protection given by the coolant in the system.
CRANKSHAFT
Fig. 1-22.
Overhead cam V-type engine timing chain arrangement.
Summary of Contents for ASE-A8
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