Volvo Maintenance Hints for 7xx/9xx - Bill Garland's Nuclear ...

Poor idle, Smoke, Oil Leaks: Clogged Flame Trap [Symptoms:] Smoke out the
tailpipe, gradual oil loss, fouled plugs, valve cover gasket or main oil seal leakage.
[Tip: Bob Savasta, Motor Magazine, Jul y 2001] These are classic symptoms of a bad
PCV or flame trap system, which is clogged with sludge or carbon.
Fuel Intake Carbon Removal.
Problems With Valve and Injector Deposits. [Motor Magazine, Dec 2002] As a vehicle
approaches higher mileage, you can generally expect intake valve deposits (IVDs)
and injector deposits. Their onset can vary widely, depending on driving conditions.
Engine operating temperature, intake manifold gas speed (rpm) and hot soak cycles
are some of the critical operating parameters affecting these deposits. To lubricate an
intake valve, tiny amounts of oil have to run down the valve stem. Over time, this oil is
deposited and heated on the intake side of the valve, forming a carbon cone. This has
multiple effects on the intake event. The carbon changes the aerodynamics of the
intake event - causing higher gas speed and a change in the direction of intake and
swirl - which affects the combustion process. The IVDs also act like a sponge, creating
a delay in fuel control. This delay not only creates a temporary enleanment on
acceleration but also causes a temporary enrichment on deceleration. When the
throttle is closed, the intake manifold vacuum goes high, pulling the fuel out of the
carbon sponge. This affects fuel control. When the engine is shut off, a small amount
of liquid fuel is left on the tips of the injectors; this fuel evaporates and leaves behind
solids that were originally dissolved in the fuel). Eventually, these deposits cause an
injector to act like a squirt gun rather than an atomizer. Aggressive drivers and drivers
with long highway drive cycles may not have deposit issues until very high mileages.
Stop & go drivers, especially delivery drivers with many hot-soak cycles, are more
likely to experience deposit problems sooner.
See the FAQ Section on Fuels and Lubricants for more information.
Carbon Removal in Injectors, Intake Manifold, Valves and Cylinders:
Gasolines with Detergents. In the United States, the new Top Tier gasolines are
certified to have adequate detergent levels to remove intake system deposits as
determined by the Top Tier group of GM, BMW, Honda, and Toyota. See their website
at http://www.toptiergas.com/
Gasoline Additives. BG44K is the heavy duty stuff - and recommended in Volvo and