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Chapter 32 Intake and Exhaust Systems Vacuum Systems • Vacuum in the intake draws air into the cylinders • Also used to operate or control systems and/or components • Vacuum is supplied by a network of hoses, tubes, and control valves 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 on a pressure gauge, or psig • Vacuum expressed in inches of mercury (in Hg), kilopascals, or bars Normal atmospheric pressure at sea level is about 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 Backfiring Poor acceleration Overheating Pinging Poor fuel economy Poor starting Rough idle Rich or lean stumble Detonation or knock Rotten egg odor Diagnosis and Troubleshooting (cont’d) • Inspect for: – – – – – – Improper routing Disconnections Cuts Kinks 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 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 converter • Exhaust gaskets or seals are used to prevent leaks between components • Most gaskets and seals need replaced if the exhaust pipe is being replaced 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 Mufflers • Has baffles, chambers, tubes, or holes to break up sound • Two common types: – Reverse flow – Straight through flow • Produces some backpressure, which affects engine breathing Resonator • Acts as a second muffler or silencer • Further reduces exhaust noise • Located toward the end of the exhaust system • Looks like a small muffler Tailpipe • 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 ... vacuum that draws the exhaust out of the cylinder Exhaust Pipe and Seal • Runs between the exhaust manifold and catalytic converter • Exhaust gaskets or seals are used to prevent leaks between... 1500 rpm Exhaust System Components • Exhaust manifold • Exhaust pipe and seal • Catalytic converter • Muffler • Resonator • Tailpipe • Heat shields • Clamps, brackets, and hangers • Exhaust gas...Vacuum Systems • Vacuum in the intake draws air into the cylinders • Also used to operate or control systems and/ or components • Vacuum is supplied by a network of hoses, tubes, and control