Automotive Technology/Engine Repair
This section should guide you to take the ASE test A1 for engine repair.
|Questions||15 ||10 ||10|| 8 ||7 ||50 | |Percentage||30% ||20% ||20% ||16% ||14% ||100%|
A. General Engine DiagnosisEdit
A.1 Verify driver’s complaint and/or road test vehicleEdit
- Always road test the vehicle, before and after
- A.2 Determine if no-crank, cranks but will not start, or hard starting condition is an engine mechanical problem, or is caused by another vehicle subsystem.
No Crank-Mechanical: remove the serpentine belt and try to physically rotate the crankshaft by hand. If you are unable to rotate the crankshaft by hand with the serpentine belt removed, try using a breaker bar with a socket that fits the crank bolt. Not being able to turn the crankshaft by hand with the serpentine belt remove is a good indication of mechanical failure, and not being able to turn the crankshaft with the serpentine belt removed even with a breaker bar is an almost infallible way to know their has been a mechanical failure of some sort.
No Start-Electrical: if the battery isn't producing enough power to spin the starter, you will hear an odd clicking sound when you turn the key to crank the engine.
Crank, No Start-Mechanical: if the engine cranks but will not start, one or more of the following mechanical issues may be the culprit: Improper crankshaft and/or camshaft timing, holes in valves/pistons/cylinder walls, damaged connecting rods, damaged valve springs, damaged spark plug, damaged injector, and so on, and so on.
Crank, No Start-Electrical:
Hard Start-Mechanical: mechanical issues that can cause hard starting can include: intake valve deposits, clogged fuel filter, faulty fuel pump, and so forth. Essentially any mechanical issue related to hard starting is related to the engine getting too much or not enough fuel/air. To diagnose a fuel related mechanical problem, spray starting fluid into the intake and see if the engine starts more quickly. If it starts more quickly when starting fluid is introduced through the intake, the engine is receiving sub-optimal amounts of fuel into the combustion chamber. This can be the result of a clogged fuel injector/filter, or a weak/faulty fuel pump, or a leaking fuel line. To diagnose an air related mechanical problem, put an additive such as Valvoline Total Fuel Injector Cleaner into your gas tank. This is supposed to clean any intake valve deposits. It will take between 2-4 fill ups before any real difference in the time it takes to start the engine is noticed. If the engine starts more quickly after putting the additive into your tank 2-4 times, the intake valve deposits were the problem.
Hard Start-Electrical: electrical issuses that cause hard starting can include: faulty sensors, spark plugs/wires, cap and/or rotor, and so forth. Testing for bad sensors can be done with a scan tool and/or a visual inspection of the sensors. Spark plugs should be removed and visually inspected. It is almost never a bad idea to change your spark plugs. Spark plug wires should be visually inspected for cracks in the insulation. Another trick is to mist the wires with water at night and have an assistant crank the engine. Any cracks in the insulation will present themselves as visible sparks caused by the wires grounding to the block before they reach the spark plug. A visual inspection of the cap and rotor can sometimes produce resutls, but more often than not these will need to be tested for continuity.
- A.3 Inspect engine assembly for fuel, oil, coolant, and other leaks
- A.4 Isolate engine noises and vibrations
Engine Noise: use a mechanic's stethoscope or chassis ears to identify where the noise is coming from. If the noise is coming from the top of the engine, for example, if a repetitive tapping noise is heard, this usually signifies a problem with the valvetrain. If the sound seems to be coming from the middle of the engine, perhaps making a light knocking noise, this can be due to piston carbon buildup. If the sound is coming from the bottom of the engine, and makes a very deep knocking noise. this signifies problems inside the engine block i.e. broken piston, thrown rod, spun bearing, and so on. If the sound is coming from the rear of the engine, it may be the flexplate has cracked. The noise is hard to hear at idle, but gets more noticeable the more load is put on the engine.
Engine Vibration: Good engine mounts are meant to isolate engine vibrations from the rest of the vehicle. If any of these mounts are damaged, these engine vibrations can usually be felt by the driver and/or passengers.
- A.5 Diagnose the cause of excessive oil consumption, coolant consumption, unusual engine exhaust color, and odor.
- Excessive Oil Consumption: this can be diagnosed by running shop air through the spark plug hole with the piston at Top Dead Center (TDC). If air sounds like it is escaping back through the intake manifold, then the most likely culprit is a bad intake valve. If air sounds like it is escaping through the exhaust manifold, then the most likely culprit is the exhaust valve. If air sounds like it is getting past the piston, it may be the rings are bad, or the piston itself has a hole in it, or the cylinder wall has a hole in it. Any of these conditions have the potential to create an excessive oil consumption scenario.
- Excessive Coolant Consumption: a tailpipe spewing plumes of white smoke is a sure sign of excessive coolant consumption. Check your coolant level at the radiator. If it is low, this does not necessarily indicate a coolant consumption issue, but is a good first step. If a milky substance is found in the coolant, this is often a sign of oil mixing with the coolant and is usually caused by a crack somewhere in the engine or may indicate a blown head gasket. External coolant leaks are easily identifiable due to the distinct coloration of today's coolants.
- Exhaust Color: plumes of white smoke coming from the tailpipe indicate coolant is being burned in the combustion chamber. Blue-grey smoke indicates oil is being consumed in the combustion chamber. Rotten egg smell from the tailpipe indicates a bad catalytic converter.
- A.6 Perform engine vacuum tests.
- Engines should have 17 -22 inches of vacuum
- Vacuum gauge should be connected to intake manifold
|Inches of Vacuum tested||Indication|
|11-16 in Hg||Idle Mix or Fuel Injectors|
|12-18||Leaking or Burnt Valve|
|10 -25||Weak Valve Springs|
|7-20||Leaking Head Gasket|
- A.7 Perform Cylinder Power Balance Tests.
- If the rpm drop for one cylinder is not the same as the others, there is a problem with that cylinder.ne cylin
- A.8 Perform cylinder cranking compression tests.
- Disable Fuel and Injection before test
- Lock Wide Open Throttle
- Crank Four(4) compression strokes for each cylinder
- No Compression indicates a burned exhaust valve or a hole in a piston, see blowby
- Compression variation more than 20% indicates problem
- Compression is higher than spec indicates carbon deposits
- Compression is low, perform a wet compression test
- Add oil to the cylinder via spark plug opening, Crank, Retest
- Compression is higher indicates worn rings
- A.9 Perform cylinder leakage tests; determine necessary action.
- Uses compressed air to test a closed cylinder
- Problem if leakage exceed 20%
- Air from Tailpipe indicates Exhaust Valve leak
- Air from PCV Valve indicates a Piston Ring leak
- Air from throttle body indicates Intake Valve Leak
- Air from radiator cap indicates Head Gasket Leak or cracked head
B. Cylinder Head and Valve Train Diagnosis and RepairEdit
- Remove cylinder heads, disassemble, clean, and prepare for inspection.
- Visually inspect cylinder heads for cracks, warpage, corrosion, leakage, and the condition of passages.
- Inspect and repair damaged threads where allowed; install core and gallery plugs.
- Inspect, test, and verify valve springs for squareness, pressure, and free height comparison; replace as necessary.
- Inspect valve spring retainers, rotators, locks/keepers, and lock grooves.
- Replace valve stem seals.
- Inspect valve guides for wear; check valve stem-to-guide clearance; determine needed repairs
- Inspect valves and valve seats; determine needed repairs.
- Check valve spring installed (assembled) height and valve stem height; determined needed repairs.
- Inspect pushrods, rocker arms, rocker arm pivots, and shafts for wear, bending, cracks, looseness, and blocked oil passages; repair or replace as required.
- Inspect and replace hydraulic or mechanical lifters/lash adjusters.
- Adjust valves on engines with mechanical or hydraulic lifters.
- Inspect camshaft(s) (includes checking drive gear wear and backlash, end play, sprocket and chain wear, overhead cam drive sprocket(s), drive belt(s), belt tension, tensioners, camshaft reluctor ring/tone-wheel, and variable valve timing components); replace as necessary.
- Inspect and measure camshaft journals and lobes; measure camshaft lift.
- Inspect and measure camshaft bore for wear, damage, out-of-round, and alignment; determine needed repairs.
- Inspect valve timing; time camshaft(s) to crankshaft.
- Inspect cylinder head mating surface condition and finish, reassemble and install gasket(s) and cylinder head(s); replace/torque bolts according to manufacturers’ procedures.
Engine Block Diagnosis and RepairEdit
- (10 questions)
- Remove and disassemble engine block; clean and prepare components for inspection and reassembly.
- Visually inspect engine block for cracks, corrosion, the condition of passages, core and gallery plug hole condition, surface warpage, and surface finish and condition; inspect piston oil cooling nozzle/jets for damage, improper alignment and restriction; determine necessary action.
- Inspect and repair damaged threads where allowed; install core and gallery plugs.
- Clean and inspect cylinder walls; measure cylinder bore; determine need for further action.
- Inspect crankshaft for end play, journal damage, keyway damage, thrust flange and sealing surface condition, and visual surface cracks; check oil passage condition; measure journal wear; check crankshaft reluctor ring/tone wheel (where applicable); determine necessary action.
- Inspect main bearing wear patterns; inspect and measure main bearing bores and cap alignment; mark caps for location and direction; clean and inspect crank girdle (bed plate/ladder) where applicable.
- Install main bearings and crankshaft; check bearing clearances and end play; inspect, replace, and torque bolts according to manufacturers’ procedures.
- Inspect camshaft bearings for excessive wear and alignment; replace bearings if necessary; install camshaft, timing chain and gears; check end play.
- Inspect auxiliary (balance, intermediate, idler, counterbalance, or silencer) shaft(s), drive(s)/gear(s), and support bearings for damage and wear; time balance shaft to crankshaft; determine necessary action.
- Inspect, measure, service, or replace pistons and piston/wrist pins; identify piston and bearing wear patterns caused by connecting rod alignment problems; determine necessary action
- Inspect connecting rods and bearings for damage, bore condition, and pin fit; mark caps for location and direction; determine necessary action.
- Inspect, measure, and install or replace piston rings; assemble piston and connecting rod; install piston/rod assembly; check bearing clearance and sideplay; install connecting rod bearings; inspect, replace, andtorque fasteners according to manufacturers’ procedures.
- Inspect, reinstall, or replace crankshaft vibration damper/harmonic balancer (includes dual-mass damper). #Inspect crankshaft flange and flywheel mating surfaces; inspect and replace crankshaft pilot bearing/bushing (if applicable); inspect flywheel/flexplate and flywheel ring gear for cracks and wear (includes dual-mass flywheel); measure flywheel runout; determine necessary action.
- Inspect and replace pans and covers.
- Assemble the engine using gaskets, seals, and formed-in-place (tube-applied) sealants, and thread sealers, according to manufacturers’ specifications; reinstall engine.
Lubrication and Cooling Systems Diagnosis and RepairEdit
- (8 questions)
Diagnose engine lubrication system problems; perform oil pressure tests; determine necessary action.Edit
- Disassemble and inspect oil pump (includes gears, rotors, housing, and pick-up assembly); measure oil pump clearance; inspect pressure relief devices and pump drive; determine necessary action.
- Inspect, test, and flush or replace internal and external engine oil coolers.
- Fill crankcase with oil and install engine oil filter.
- Perform cooling system pressure tests; perform coolant dye test; determine necessary action.
- Inspect and test radiator, heater core, pressure cap, and coolant recovery system; replace as required.
- Inspect, replace, and adjust drive belt(s), tensioner(s), and pulleys.
- Inspect and replace engine cooling system and heater system hoses, pipes and fittings.
- Inspect, test, and replace thermostat, coolant by-pass, and thermostat housing.
- Inspect and replace water pump.
- Inspect and test coolant; drain, flush, and refill cooling system with recommended coolant; bleed air as required.
- Inspect and test fan (both electrical and mechanical), fan clutch, fan shroud, air dams, and cooling fan electrical circuits; repair or replace as required.
- odb2 codess
Fuel, Electrical, Ignition, and Exhaust Systems Inspection and ServiceEdit
- (7 questions)
Inspect, clean or replace fuel injection system components, intake manifold, and gaskets.Edit
- Fuel Injection System
- Intake Manifold
Inspect, service or replace air filters, filter housings, and intake ductwork.Edit
Inspect turbocharger/supercharger systems; determine necessary action.Edit
Test engine cranking system; determine needed repairs.Edit
Inspect and test crankcase ventilation system components; replace as necessary.Edit
Inspect and test ignition system components; replace as necessary; verify timing.Edit
- Ignition system