CH32 intake and exhaust systems STUDENT VERSION rev

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Chapter 32

Intake and Exhaust Systems

Vacuum Basics

• Vacuum refers to any pressure lower than atmospheric pressure

• Higher altitude = Lower pressure

• Pressure at sea level is 14.7 psi

• 14.7 psi is usually 0 on a pressure gauge, or

0 psig

• Vacuum expressed in inches of mercury (in Hg), kilopascals, or bars

Normal

atmospheric pressure at sea level is about 1 bar

or 100

kilopascals

Engine Vacuum

• It is produced by the downward movement

of the piston on the intake stroke

• The amount depends on the cylinder’s

ability to form a vacuum and the intake’s ability to fill the cylinder

Diagnosis and Troubleshooting

• Vacuum problems can produce or contribute

to the following symptoms:

Stalling Poor starting

Backfiring Rough idle

Poor acceleration Rich or lean stumble

Overheating Detonation or knock

Pinging Rotten egg odor

Poor fuel economy

Diagnosis and Troubleshooting

– Wear near hot spots

– Damaged valves, storage devices

Air Induction System

• Directs and filters outside air into the

cylinders

• Make sure intake ductwork is properly

installed and all connections are airtight

• Air leaks after the airflow sensor will cause drivability problems

Intake Manifolds

• Distribute the clean air or air-fuel mixture

as evenly as possible to each cylinder

• Can be classed wet or dry manifolds

• Often house the thermostat and EGR

• Modern manifolds are aluminum or plastic

• Designs vary by engine type

Design Variations

• Runner length is designed to achieve the best performance at particular speeds

• Short runners – more HP at higher speeds

• Fast moving air enters intake and stops at closed intake valve

• This air then bounces around in the runner

Variable Intake Runners

• PCM controls plenum area and/or length of runners according to engine speed

• Increases volumetric efficiency at more than one range of engine speed

• Common use is changing path of air

between short and long runners

Forced Induction Systems

• Engines can not produce full power at high speeds because the do not receive enough air

• Power output is related to the amount of air compressed in the cylinders

• More power can be produced by pressurizing the intake mixture before the cylinder

• Turbo and superchargers accomplish this

• Exhaust driven air pumps

• Exhaust gases spin the turbine blades

• The turbine turns the compressor wheel

• Air is compressed and sent to the cylinders

• Used on gas and diesel engines

Turbocharger Components

• Turbine (hot wheel)

• Turbine shaft

• Compressor (cold wheel)

• Waste gate valve

• Actuator

Typical Turbocharger System

• The turbine spins at very high speeds

• The waste gate controls the pressure of air delivered to the cylinders

• Typically begins to compress air around

2000 engine RPM

• Turbo boost describes the positive pressure

• 10 psi of boost equals 24.7 psi

Turbo Lubrication and Cooling

• The turbo must be well lubricated and

cooled – exhaust temperatures can surpass 1800ºF (982ºC)

• Compressor wheels can spin up to 100,000 RPM

Turbocharger Inspection

• Listen to sounds from the turbo system

• Inspect the exhaust system for leaks

• Check for intake system leaks

• Waste gates may have carbon buildup

• Check ignition timing, vacuum hoses, knock sensor, and O2 sensor

• Engine oil and filter must be maintained

• Many manufacturers recommend specific types of oil

• Run the engine for at least 30 seconds after the oil change

• Ensure the air cleaner is maintained

Turbo Start-Up and Shutdown

• Leading cause of failure is poor lubrication

• If engine has not run for a day or more, start and let idle 3 – 5 minutes

• Never operate under load if there is less

than 30 psi oil pressure

• Idle the engine for 20 – 120 seconds before shutdown

Supercharger Operation

• Air enters from a remote mounted air

cleaner and airflow meter

• Once past the throttle plates, air passes through the inlet plenum

• Air is pressurized by the spinning rotors

• The heated air then passes through an intercooler

Air flow through a supercharger

Supercharger Bypass System

• May be electronically or vacuum controlled

• The bypass allows the supercharger to idle when power is not needed

• With the bypass closed, boost can reach

about 12 psi

• Normally superchargers have their own oil supply

• Check and correct oil level periodically

• Inspect regularly for leaks

• Inspect induction system for leaks and filter condition

Supercharger + Turbocharger

• A few vehicles use a “twincharger” system

• The supercharger boosts power at low

speeds

• The turbo boosts power at high speeds

• Used on direct injection engines

• Maximum boost is around 36 psi at 1500 rpm

Exhaust System Components

• Exhaust gas oxygen sensors

Exhaust Manifold

• Collect and direct exhaust gases

• Can be cast iron or stamped steel

• Designed for particular engine/chassis

combinations

• Proper tuning can create a partial vacuum that draws the exhaust out of the cylinder

Exhaust Pipe and Seal

• Runs between the exhaust manifold and

Catalytic Converters

• Located before the muffler

• The extreme heat in the converter oxidizes the exhaust

• Converts undesirable exhaust gases into harmless gases

• Reduces exhaust noise

Catalytic Converters (cont’d)

• Late model vehicles use a three-way

converter (TWC)

• Treats all three controlled emissions

Converter Problems

• Can be damaged or plugged

• Often caused by overheating due to raw fuel entering the converter

• A plugged converter restricts exhaust flow

• Function can be checked with exhaust gas analyzer

• Use a vacuum or back pressure gauge to

check for restriction

– Straight through flow

• Produces some backpressure, which affects engine breathing

• Acts as a second muffler or silencer

• Further reduces exhaust noise

• Located toward the end of the exhaust system

• Looks like a small muffler

• Last pipe in the system

• Releases exhaust gases beyond the backend

of the vehicle

Heat Shields

• Protect other parts

from exhaust heat

• Usually made of

pressed or perforated

sheet metal

Clamps, Brackets, and Hangers

• Used to properly join and support the

exhaust system

Exhaust System Inspection Items

• Holes, road damage, and split seams

• Kinks or dents

• Discoloration or rust

• Broken or missing hangers

• Loose tailpipes or other components

• Signs of catalytic converter overheating:

– Bluish or brownish converter shell

Exhaust Restriction Test

• Most common check is with a vacuum gauge

• Connect gauge to manifold vacuum

• Bring engine up to 2000 – 2500 RPM

• Watch gauge:

– Reading should stay high and steady

– A falling reading indicates a restriction

Replacing Components

• Check clearance points

• Make sure new parts match the old parts

• Allow the system to cool

• Soak all rusted fasteners with a penetrating oil