2. Diagnosing Engine Problems Brake Systems- level: 2 Engine Construction Topics covered in this presentation: ◼ ◼ ◼ ◼ compression test Leakage and vacuum tests Smoke test Emission analyzer test Brake Systems- level: 2 2. Diagnosing Engine Problems Technician A says that the Otto-cycle gasoline engine has four strokes per cycle. Technician B says that the crankshaft makes four revolutions a. Technician A only b. Technician B only c. Both A and B d. Neither A nor B Brake Systems- level: 2 2. Diagnosing Engine Problems Technician A says that the purpose of the flywheel is to control the twisting of the crankshaft. Technician B says that the purpose of the vibration damper is to help provide a continuous flow of power. Who is right? a. Technician A only b. Technician B only c. Both A and B d. Neither A nor B Brake Systems- level: 2 2. Diagnosing Engine Problems Technician A says that the crankshaft turns 720 during one four-stroke cycle. Technician B says that the camshaft turns 360 during one four-stroke cycle. Who is right? a. Technician A only b. Technician B only c. Both A and B d. Neither A nor B Brake Systems- level: 2 2. Diagnosing Engine Problems Technician A says that an in-line six-cylinder engine is usually longer and heavier than a V8 engine of the same displacement. Technician B says that there are twice as many teeth on the crankshaft sprocket as there are on the camshaft sprocket. Who is right? a. Technician A only b. Technician B only c. Both A and B d. Neither A nor B Brake Systems- level: 2 2. Diagnosing Engine Problems Technician A says that “blowby” consists of gases that leak past the valves. Technician B says that blowby reduces the pressure in the crankcase. Who is right? a. Technician A only b. Technician B only c. Both A and B d. Neither A nor B 2. Diagnosing Engine Problems Brake Systems- level: 2 Testing for Compression Loss For an engine to run, it must have three things: • Sufficient compression • Fuel (in a flammable ratio to air) • Ignition (timed at the appropriate instant) One of the most common and least expensive pieces of test equipment is the compression tester. A compression tester is simply a pressure gauge that is inserted into a spark plug hole. 2. Diagnosing Engine Problems Brake Systems- level: 2 Compression Test Procedure Keep spark plug cables, or coil-over plugs, in order for the correct reassembly. Use caution when removing spark plug cables. First, twist the rubber boots to loosen them from the spark plugs. Clean around all the spark plugs with compressed air. Then remove all spark plugs, so that the starter can crank the engine easily. Insert the compression gauge into a spark plug hole. Crank the engine through at least four compression strokes. Check and record each pressure reading. 2. Diagnosing Engine Problems are performing equally and engine performance is acceptable, the engine passes the test. Brake Systems- level: 2 Interpreting Compression Test Results. If all cylinders When compression test specifications are available, they are only an estimate. If specifications are not available, locate the compression ratio in the specification manual and use the following formula: Variations in compression among cylinders should be no more than 20%. 2. Diagnosing Engine Problems Brake Systems- level: 2 When two cylinders next to each other have low compression, a blown head gasket is usually indicated. Wet Compression Test. When cylinders show poor results, perform a wet compression test. Squirt about a tablespoon of oil into each low cylinder. The oil makes a seal around worn rings, boosting the compression reading. When cylinder readings are low but increase to normal during a wet test, a piston ring problem is indicated. 2. Diagnosing Engine Problems Brake Systems- level: 2 Cylinder Leakage Test (CLT) The cylinder leakage test can accurately pinpoint causes of leakage. Regulated compressed air is introduced into the cylinder through its spark plug hole. The piston is positioned at TDC on the compression stroke, ensuring that both valves are completely closed. An acceptable leakage reading on the tester’s gauge is usually less than 10% to 15%, although vehicles with up to 30% leakage might still be performing to the owner’s satisfaction. 2. Diagnosing Engine Problems Brake Systems- level: 2 If a cylinder shows high leakage, listen to locate the sound of the leaking air. The following lists cylinder leakage test results Here are some possible locations for leaking air and the likely causes: Oil filler = leaking rings or piston Manifold intake = leaking intake valve Exhaust pipe = leaking exhaust valve Bubbles in the radiator = blown head gasket, or a crack in the head or block, which allows the regulated air to enter the cooling system Brake Systems- level: 2 2. Diagnosing Engine Problems 2. Diagnosing Engine Problems Brake Systems- level: 2 Engine Vacuum Intake manifold vacuum can be very useful in determining engine problems. Vacuum readings compare pressure in the intake manifold to atmospheric pressure. Vacuum is measured in either inches of mercury (in. Hg) or millimeters of mercury (mm Hg) or kilopascals (kPa). The vacuum gauge is connected to a manifold vacuum source. 2. Diagnosing Engine Problems Brake Systems- level: 2 Throttle plate opening controls the amount of air that can enter the engine. Movement of the accelerator pedal opens or closes the throttle plate, changing engine vacuum. vacuum should Range from 16 to 22 in. Hg at idle At idle, with the throttle plate nearly closed, engine vacuum will be high. At medium throttle opening, when cruising, engine vacuum will be close to 8–10 inches. At WOT, engine vacuum is zero. 2. Diagnosing Engine Problems Brake Systems- level: 2 To test for weak piston rings: Raise the engine speed to about 2,000 rpm. Snap the throttle closed and watch for an increase of 2–6 inches of vacuum above normal. Worn rings will not increase vacuum sufficiently during deceleration. Generally, the higher the rise, the better the condition of the rings. Brake Systems- level: 2 2. Diagnosing Engine Problems Sticky valves are indicated when the needle drops quickly or drifts. It could be because valves are hanging up in their guides rather than closing freely The most common cause is oxidized gasoline. A lack of proper lubrication during cylinder head assembly can also result in sticky valves. Leaking valves are indicated when the needle drops at regular intervals. Brake Systems- level: 2 2. Diagnosing Engine Problems 2. Diagnosing Engine Problems Brake Systems- level: 2 Smoke Testing Smoke testers are popular diagnostic devices for finding vacuum, oil, cooling, and exhaust leaks A smoke machine generates thick, white smoke at a pressure of 1–1.5 psi. 2. Diagnosing Engine Problems Brake Systems- level: 2 Emission Analyzer Test Shops that do engine performance and emission control work have an infrared exhaust gas analyzer that can be used to check for a collapsed piston skirt or piston ring or cylinder damage. With the engine idling, individually short out each cylinder and record the HC reading. The HC reading should increase as each cylinder is shorted out, but a significantly higher reading indicates a problem cylinder. 2. Diagnosing Engine Problems Brake Systems- level: 2 ENGINE NOISES Noises can be located by listening through a stethoscope. The end of a large screwdriver, a piece of hose, and a long wooden dowel are other listening tools to help pinpoint noises. An amplified stethoscope is very effective as well Brake Systems- level: 2 2. Diagnosing Engine Problems It is important to try to determine the location of noises before disassembling the engine. There have been cases where engines have been disassembled, inspected, and rebuilt, and when reinstalled in the car, still had the same problem Noises are often transmitted from their origins to other locations and can be difficult to locate. Belts are a common source of noise. If you suspect a belt of making noise, disconnect the belt and run the engine for a short time, or spray soapy water on the belt while the engine runs to see if the noise changes. Brake Systems- level: 2 2. Diagnosing Engine Problems 2. Diagnosing Engine Problems Brake Systems- level: 2 Crankshaft Noises Crankshaft noises can be caused by a variety of things. They are generally deeper in pitch than other engine noises. It is important to isolate the source of the noise so that an accurate diagnosis can be made • Front Main Bearing Knock. Excessive front main bearing clearance results in a heavy knock when the engine warms up. The knock is generally most pronounced at 1,500–2,500 rpm. Loosening accessory drive belts will often reduce the intensity of the knock. • Thrust Bearing Knock. End thrust is movement of the crankshaft in a forward and backward direction. The crankshaft has a machined surface that controls end thrust. It can be worn, allowing the crank to move back and forth. Excessive end thrust will cause a clunk to happen when the vehicle leaves a stop sign. • EGR Valve Knock. When there is a low-speed knock, check the EGR valve by manually opening the valve and accelerating the engine to about 2,000 rpm to see if the noise disappears. If it does, replace the EGR valve. 2. Diagnosing Engine Problems Brake Systems- level: 2 Exhaust Gas in the Coolant. The tester samples air in the filler neck of the radiator. The combustion leak tester is used with the engine running. Carbon monoxide (CO) exhaust gas in the radiator will change the color of the liquid in the tester. Brake Systems- level: 2 2. Diagnosing Engine Problems If compression is too low or if coolant entering the cylinder causes the plug not to fire, the tester will not give a reading. The block check tester can sometimes give a false reading with coolant. It works best on pure water. To perform this test, lower the coolant level until it is at least 2 inches below the radiator filler neck. The bulb of the tester is squeezed repeatedly for about 1 minute to force gases in the radiator through the fluid in the tester. If the color of the blue-green fluid changes to yellow, a combustion leak is indicated. If the fluid remains blue-green, a leak is not present at that moment. When test results are positive on a V-type engine, disable all spark plugs to one bank of cylinders. 2. Diagnosing Engine Problems Brake Systems- level: 2 Allow the engine to idle for 5 minutes to purge all gases that might remain in the cooling system from the first test and then retest. If the test is negative, the leak is from the disabled bank of cylinders and that head can be removed for repair. If the test is positive, be sure to repeat the test on the other bank of cylinders before removing the head. Both heads are independent of each other and could have leaks. Brake Systems- level: 2 2. Diagnosing Engine Problems Brake Systems- level: 2 2. Diagnosing Engine Problems An infrared exhaust analyzer can also be used to check for exhaust gas in the coolant Hold the probe over the radiator filler neck to check for HCs in the coolant. Be sure not to suck coolant into the tester probe. If there is CO in the cooling system, exhaust gas is leaking in during combustion. 2. Diagnosing Engine Problems Brake Systems- level: 2 Cooling System Pressure Test The system is pressurized with the engine off. The pressure should remain stable A pressure tester can also pinpoint the location of a leaking core plug. Use a flashlight and an inspection mirror to pinpoint the leak. Experienced technicians will not begin a repair until they are positive of the locations of leaks. 2. Diagnosing Engine Problems Brake Systems- level: 2 OIL PRESSURE PROBLEMS Low oil pressure can ruin an otherwise good engine in a short time. A faulty oil pressure sending unit is sometimes the cause of a low oil pressure reading on an electric dash gauge or light. Pressure can be tested by temporarily installing a gauge in place of the sending unit. Use an oil sending unit socket to remove the sender because pliers can damage it. Brake Systems- level: 2 2. Diagnosing Engine Problems Thank you Ahmad Mustafa Aboul-Yazid