МАЪРУЗА 2 ИЁД ёниш камерасини сиқиш даражасини аниқлаш Compression Test of the Combustion Chamber Made by JPI and based recommendation prof.gabriel Anghelache
Content 1. Introduction 2. Compression Tests Methods 3. Equipment 4. Operations 5. Results 6. Conclusion
Introduction Typical Engine-Related Complaints Typical engine mechanical-related complaints include the following: Excessive oil consumption Engine misfiring Loss of power Smoke from the engine or exhaust Engine noise
Introduction The Engine Torque Depends on Cylinder Pressure Pressure generated in the cylinder creates torque at the crankshaft; Torque is directly proportional to cylinder pressure; Any compromise in cylinder pressure causes a corresponding loss in torque; Many drivability problems stem from inadequate cylinder pressure;
Introduction Cylinder Pressure Failure Modes Cylinders can fail to produce adequate pressure for two reasons: Blow-by; Misfire; Blow-by is a mechanical problem; Misfire may be either mechanical, electrical, or chemical in origin;
Introduction Compression Test One of the fundamental engine diagnostic tests that can be performed. An engine can lose compression by leakage of gas through one or more of the following routes: Intake or exhaust valve Piston rings Piston crown, if there is a hole The rings zone of piston Cylinder surface (weared or cracked) Cylinder head gasket
Introduction Combustion Leakage
Compression Tests Methods Quantitative methods Using compression tester; Qualitative methods Measuring the current drawn by the starter motor; Comparing engine speeds when the engine is cranked over by the starter; Comparing engine speeds on idle; Comparing corrected quantity of fuel injected in each cylinder;
Equipment Compression Tester Kit Tools and equipment: - compression gauge; - an air nozzle; - an oil pump (syringe); - the socket ratchets and extensions that may be necessary to remove the spark plugs from the engine; compression gauge
Equipment Compression Tester Recording card support * Recording card The compression gauge Hose Engine rotation control mechanism Mechanism to release/restrain the pressure inside the gauge Fitting on the end that actually screws into the spark plug opening and seals with an "O"- ring.
Equipment Measuring the Current Drawn by the Starter Motor Measurement Monitor the computer module Printer Trolley Tested car Bosch FSA 740
Equipment Comparing Engine Speeds and Quantity of Injected Fuel Tested car KTS: Bosch OBD Tester
Operations Compression Tester visual inspection of oil level and condition; check conditions for: battery; electrical wires and connectors of the cracking system; starter; air filter; pc [bar] Lower engine speed more time for gas leakage higher gas leakage*
Operations Compression Tester the engine should be warmed up to normal operating temperature before testing*; disable the ignition system and the fuel-injection system to prevent the squirting of fuel into the cylinder*;
Operations Compression Tester - lock the throttle open (and choke, if the engine is equipped with a carburetor) to ensure that enough air will be drawn into the engine; - before removing the spark plugs, use an air nozzle to blow away any dirt that may be around the spark plug*. *
Operations Compression Tester - remove all of the spark plugs; - select the proper adapter for the compression gauge; - if necessary, connect a battery charger to the battery before starting the compression test*.
Operations Compression Tester the tester is screwed or held in to each spark plug hole; the engine is cranked by the starter motor until a peak pressure is stabilized on the tester; release the pressure from the gauge; move the support of the recording card for next cylinder; repeat the operations to other cylinders*.
Operations Compression Test - record the highest readings.* Wet Compression Test - for low compression on one or more cylinders: three squirts of oil into the cylinder and retest;*
Operations Relative Compression - Measuring the Current Drawn by the Starter Motor The amperage required to crank the engine depends on: - the capacity of the engine; - the number of cylinders; - the viscosity of the oil; - the condition of the starter motor; - the condition of the starter s wiring circuit; - the temperature of the engine; - the compressions in the cylinders.
Operations Relative Compression - Measuring the Current Drawn by The Starter Motor Checking*: - the battery is charged; - the starter and associated circuit are in good condition; - the engine is warmed up; - the engine is prevented from the starting: the fuel pump fuse (no 24) or fuel pump relay is removed;
Operations Relative Compression - Measuring the Current Drawn by the Starter Motor the arrow shows correct clamp position; the For voltage and current measurement, the battery leads of the measurement system are connected to the battery : - the black lead is connected to the negative battery clip; - the red lead is connected to the positive battery clip; - the 1000 AMP current clamp is clamped around the cable between battery and starter motor ;
Operations Relative Compression - Measuring the Current Drawn by the Starter Motor In the Test Procedures of the FSA software, the test step Battery/starter/compression is selected
Operations Relative Compression - Measuring the Current Drawn by the Starter Motor The engine is cranked until the test results appear on the screen;
Operations Relative Compression - Comparing Engine Speeds and Quantity of Injected Fuel For the next three methods, OBD (on boar diagnostics) connection is used.
Operations Relative Compression - Comparing Engine Speeds and Quantity of Injected Fuel Comparing corrected quantity of fuel injected in each cylinder; Comparing cylinder speeds on idle speed; Comparing engine speeds when the engine is cranked over by the starter; The last three methods can be accessed by using OBD Software: Diagnostic/ Engine/ Function Tests/ These methods can be used just on cars that have this software set.
Results Compression Tester The recording card on its support
Results Compression Tester toil pc [bar] C cil. 1 cil.2 cil.3 cil.4 [%] Cold engine Warm engine Oil squirted in combustion chamber The measured pressure values Cold engine error - minimum compression pressure value is specified by the manufacturer (for BMW 318is: 10-11 bar); - difference between the highest and the lowest reading, pc, should be less than 20%; 100%;
Results Compression Tester if the minimum compression pressure value is not known) patm= 1 bar atmospheric pressure; mc = 1,3 polytropic exponent; εe effective compression ratio αliv - late closing angle of intake valve (60 0 RAC for BMW 318); ε geometric compression ratio (ε= 10 pentru BMW 318); pclim =0,8 p c teor ; pclim limit value of the compression pressure;
Results Wet Compression Tester Oil is used to help sealing around the piston rings; - if the readings are much higher than without the oil: - worn piston rings or/and cylinder. - if the readings increase only slightly (or not at all): - defective valves; - blown head gasket. - blown head gasket symptoms: - coolant leaking externally from bellow the exhaust manifold; - white smoke from the exhaust pipe; - overheating engine; - bubbles in the radiator or coolant overflow tank; - white milky oil; - significant loss of coolant with no visible leaks.
Results Relative Compression - Measuring the Current Drawn by the Starter Motor Car model tested Drawn current values for cylinders in ignition order Starter current with no compression Limit interval for measured values Current used to compress the gas from the last cylinder Evaluate the relative compressions Measure the current required to crank the engine
Results Relative Compression - Measuring the Current Drawn by the Starter Motor - values of the drawn current are noted in a table for three repeated tests; Test I Test II Test III Engine speed Current drawn [A] n, [rev/min] cyl. 1 cyl. 2 cyl. 3 cyl. 4 - current required to push each cylinder up on its compression stroke is compared; - the better the compression the higher the current demand and vice versa; - the current draw on each cylinder should be equal; - if not, the cylinder with less current drawn should be tested with a compression tester;
Results Comparing Engine Speeds When the Engine Is Cranked Over by the Starter: Compression Test Menu step - the OBD software prevents the engine from the starting; Engine speeds corresponding to each cylinder compression stroke measured before top dead center *
Results Comparing Engine Speeds When the Engine Is Cranked Over by the Starter: Compression Test Menu Step - values of the engine speeds corresponding to each cylinder are noted in a table for three repeated tests; Engine speed n, [1/min] Test I Test II Test III cyl. 1 cyl. 2 cyl. 3 cyl. 4 - the better the compression the lower the engine (cylinder) speed and vice versa. Results Comparing Engine Speeds on Idle - the engine software computes an equal quantity of injected fuel for all cylinders;
Engine speeds corresponding to each cylinder compression stroke measured after top dead center *
Results Comparing Engine Speeds on Idle - values of the engine speeds corresponding to each cylinder are noted in a table for three repeated tests; Engine speed n, [1/min] Test I Test II Test III cyl. 1 cyl. 2 cyl. 3 cyl. 4 - the better the compression the higher the engine (cylinder) speed and vice versa; - usually, this test is used to diagnose injection system.
Results Comparing Corrected Quantity of Fuel Injected in Each Cylinder - the engine software keeps the engine speed constant for all cylinders. The correction factory value has to be between 2 3 limits
Results Comparing Corrected Quantity of Fuel Injected in Each Cylinder - values of the correction factor values corresponding to each cylinder are noted in a table for three repeated tests; Test I Test II Test III Correction factor values, [mm 3 ] cyl. 1 cyl. 2 cyl. 3 cyl. 4 - the weaker the compression the higher the correction factor values and vice versa; - usually, this test is used to diagnose injection system.
Conclusion Qualitative methods: - fast diagnosis; - investigation without disassembly; - relative results; - general diagnosis of the combustion chamber; Quantitative method: - accuracy of measurement; - it is possible to find the routes of leakage; - a better image on results.