Volvo Symptom D12D US02 Service Manual page 52

Group 20
One condition for achieving specified tractive power is to
have sufficient fuel supply pressure on the low pressure
side. For information on measuring fuel pressure, see
"Supply Pressure, Fault Tracing" (Checklist B), Information
type "Diagnostics", group 2309.
The following can negatively affect fuel injection:
•
Restricted or dirty fuel filter (s) or fuel/water separator
filter
•
Faulty overflow valve
•
Worn or faulty fuel supply pump
•
Air leakage into the fuel supply pump supply line
•
Kinks or blockage in any of the fuel lines
•
Restricted vent line or valve at the fuel tank
•
Impurities in the fuel
•
Poor fuel grade
Air Supplied to the Engine
A reduced amount of air supplied to the engine means
that the fuel delivery is also reduced, and this results in
lower power output.
The supply of air to the engine may be affected by:
•
A damaged or restricted air inlet
•
A restricted or dirty air filter
•
A leaking charge air pipe (joints)
•
A leaking charge air cooler
•
A clogged charge air cooler
•
Damaged turbine wheels in the turbocharger or
turbocharger housings
•
A restricted EGR cooler (exhaust gases not adequately
cooled)
•
Defective EGR control valves
•
EGR reed valve failure (D12D)
•
Altitude
It is important that both the engine's air inlet and the
turbocharger are free from faults.
Never replace a turbocharger because of poor power
output without first determining that the turbocharger has
damaged components.
Exhaust System, Back Pressure
Restrictions on the exhaust side means that it is difficult to
emit exhaust gases, therefore causing the exhaust back
pressure to increase. This, in return, results in difficulty
getting a sufficient amount of fresh air into the cylinders to
efficiently burn the fuel being injected into the cylinders.
Fault Tracing
Temporary faults can be difficult to trace since the fault
may not occur when the vehicle is brought in to be
checked.
Fault tracing should be performed based on what the
driver has experienced. The information that the driver
has provided in conjunction with the gathering of factual
data should form the basis of how the problem should
be resolved.
Whenever possible, try to recreate the problem in an
environment and situation similar to the one described
by the driver.
Begin by determining if anything has recently happened
to the vehicle that could point to the electrical system,
48
D
The direct result of this is a lower intake manifold
pressure, inferior response, and higher fuel consumption.
An incorrectly rebuilt exhaust system with a lot of bends
may mean that the engine cannot emit its exhaust gases
freely. The same problem will arise if the exhaust system
is damaged (flattened), or if the shutter in the exhaust
pressure governor seizes or is damaged.
Compression
The compression is a good measure of the mechanical
condition of the engine. If there is sufficient compression,
the temperature in the cylinder is probably also sufficient.
Generally speaking, low compression is noticeable when
you have starting problems that worsen as the engine
gets hot or when there is blue oil smoke or abnormal
amounts of crankcase gases. A problem may be indicated
when one cylinder's compression is significantly lower
than the others.
Minor deviations between cylinders are normal.
Engine Control System
The engine control system, including sensors, should be
free from faults.
Note: When there are faults on some components, such
as the intake manifold pressure sensor, the result is a
natural reduction of the tractive power.
Evaluation
If none of these areas shows abnormal values, yet the
customer still maintains that the vehicle still has low
power, a reliable dyno test should be carried out.
If this test does not show that the vehicle has low power,
no further technical measures should be taken. Go
through the results together with the customer.
The customer's complaints could be related to the
vehicle's specification, or that the customer's references
are not comparable with the actual vehicle. If faults
can not be found on the vehicle, there could be other
circumstances that make the customer dissatisfied,
i.e. his experience of noise from the vehicle may have
changed.
If the dyno test shows that the vehicle clearly has low
power, fault tracing should continue in order to determine
in which system the fault may be.
but which does not have anything to do with the engine
control system.
For specific symptoms, see:
•
"Sudden Loss of Power" page 49
•
"Gradual Loss of Power" page 49
•
"Engine Does Not Reach Rated Speed" page 50
•
"Low Power After Vehicle Repair" page 50
"Low Power Output, Fault Tracing" page 47