Engine Troubles (SI Engines) Automobile)

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Engine Troubles (SI Engines) (Automobile)

19.7.

Engine Troubles (SI Engines)

Troubleshooting a customer’s problem requires thorough understanding of how the parts of a vehicle operate,

how they should normally appear, and how to use proper test equipment and procedures. The greatest difficulty

in troubleshooting is finding the specific cause of the problem. Once it has been identified, any qualified

mechanic can repair it.Troubleshooting charts are often available, which help to diagnose the cause of problems. The best of these-

charts are presented in the shop manuals for each vehicle. They are more specific than a general troubleshooting

chart designed for any vehicle. Moreover, most manufacturers print service bulletins for their service

technicians. These bulletins indicate problems, which frequently occur in their product line and provide details

on correction procedures. Keeping up-to-date on service bulletins is one of the best methods for a dealer

mechanic to make quick problem diagnoses and repairs to automobiles in the product line.

An important point in troubleshooting, frequently overlooked by the service mechanic, is that he does not

carefully listen to the customer’s complaint. The customer’s description, aided by a few leading questions, is of

great help in finding the customer’s problem. Once the problem is identified, tests and inspections can be made

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to determine the cause of the complaint. When the cause is identified, it can be easily corrected and rechecked.

The common engine troubles includes (i) engine does not crank ; (ii) engine cranks but does not start ; (Hi)

engine runs but missies ; (iv) engine lacks power, acceleration, or high-speed performance ; (v) engine overheats

; (vi) engine uses excessive oil or gasoline ; or (vii) engine is noisy. The causes for these problems are presented

below. Corrective actions are to be taken on each cause suitably.

Engine does not crank.

This may be due to run-down battery; open starting circuit; jammed starting motor drive on starter-motor ; jammed engine or defective engine transmission, which is not in neutral or neutral switch out of adjustment;

defective ignition system; plugged fuel filter; or plugged or collapsed exhaust system. In latest car models it may

happen if seat belt is not fastened properly or interlock is faulty.

Engine Cranks but does not start.

Cranks Slowly. In this case the causes may be partly discharged battery; defective starting motor; engine having

mechanical trouble; defective starting circuit; and defective ignition system.

Cranks at Normal Speed. Assuming that the battery and starting motor are working normal, the cause for the

trouble may be in the ignition or fuel system. The possible causes are defective ignition system; defective fuel

pump or overchoking; leakage of air in the carburettor or intake manifold ; defect in engine ; ignition coil or resistor burned out; plugged fuel filter ; and plugged or collapsed exhaust system. The engine incorporated with

fuel-injection system can have the reasons like incorrect or dirty fuel ; on fuel supply to nozzles or injection

pump ; plugged fuel return ; and pump timing off.

Engine Runs but Misses.

One Cylinder Missing. The possible reasons for this problem include defective spark plug; defective distributor

cap and spark plug cable; valve stuck open; broken valve spring; burned valve ; bent pushrod ; flat cam lobe ;

defective piston or rings ; defective head gasket ; and

intake-manifold leak. For fuel injection system plugged fuel filter ; injection-pump timing off; and incorrect or

dirty fuel are the additional reasons.

Different Cylinder Missing. The reasons for this trouble are defective distributor advance, coil, condenser ;

defective fuel system ; cross-firing plug wire ; loss of compression ; defective valve action ; worn pistons andrings ; overheated engine ; manifold heat-control valve stuck ; and restricted exhaust.

Engine Lacks Power, Acceleration, or High Speed Performance.

Hot or Cold Condition. The probable reasons for the trouble include defective ignition; loss of compression ;

excessive carbon in engine ; defective valve action ; defective fuel system specifically secondary valve not

opening; throttle valve not opening fully ; restricted exhaust; excessive rolling resistance from low tyres,

dragging brakes, wheel misalignment, etc ; heavy oil; wrong or bad fuel; transmission not downshifting, or

defective torque converter ; incorrect or dirty fuel ; restricted fuel return ; plugged fuel-tank vent; restricted fuel

supply ; plugged fuel filter ; and plugged nozzles.

Only Hot Condition. This trouble may be due to engine overheats ; choke stuck partly open ; sticking manifold

heat-control valve ; and vapour lock.

Only Cold Condition. The probable causes may be automatic choke stuck open; manifold heat-control valvestuck open ; cooling-system thermostat stuck open ; and engine valve stuck open.

Engine Idles Roughly.

The causes for this trouble include incorrect idle adjustment; PCV or EGR valve stuck open; and the reasons for

engine to lack power, acceleration, or high-speed performance.

Engine Stalls.

Stalls Cold or as it Warms UP. The probable reasons for this problem are choke valve stuck closed or does not

close ; fuel not getting to or through carburettor; idle speed set too low; throttle solenoid improperly set;

manifold heat-control valve stuck ; PCV or EGR valve stuck open ; damper in thermostatic air cleaner in


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cold-air mode stuck closed ; fuel low in tank ; incorrect or dirty fuel; limited fuel return ; injection pump timing

off; injection pump trouble ; and internal engine problems.

Stalls after Idling or Slow-speed Driving. The causes include defective fuel pump ; overheating; high

carburettor float level; incorrect idling adjustment; malfunctioning PCV or EGR valve ; and throttle solenoid

improperly set.

Stalls after High-speed Driving. The causes may be vapour lock ; carburettor venting or idle-compensation

valve defective ; engine overheats ; PCV or EGR valve stuck open ; and improperly set idle solenoid.

Excessive Oil Consumption.

The probable causes are external leaks; burning oil in combustion chamber; and high-speed driving.

Low Oil Pressure.

The causes include worn engine bearings ; engine overheatings ; oil dilution or foarming ; and lubricating-system

defects.

Excessive Fuel Consumption.

The reasons include high-speed driving; cylinder not firing; short-run operation ; carburettor leakage; excessive

fuel-pump pressure or pump leakage; stuck accelerator pump check valve ; choke partly closed after warm-up ;

idle too rich or too fast; clogged piston ; high carburettor float level ; worn carburettor jets ; stuck or dirty float

needle valve ; automatic transmission slipping or not upshifting ; loss of engine compression ; defective valve

action ; excessive rolling resistance from low tyres, dragging brakes, wheel misalignment, etc. ; and clutchslippage.

Engine Overheats.

The probable causes include lack of coolant; defective radiator hose ; defective water pump ; clogged water

jackets or radiator core ; thermostat stuck closed ; loose or broken fan belt ; insufficient oil; ignition timing late ;

high-altitude, hot-climate operation ; defective fan clutch; and valve timing late.

Engine Back Fires.

The reasons are engine overheats; carbon in engine; excessively rich or lean mixture; spark plugs of wrong heat

range ; ignition timing off; valves hot or stuck ; cracked distributor cap ; inoperative anti-backfire valve ; and

across-firing plug wires.

Engine Run-on or Dieseling.

The causes include timing advanced ; hot spots in cylinders ; engine overheats ; incorrect idle solenoidadjustment; and in diesel engine due to injection-pump solenoid not turning off fuel valve.

Smoky Engine Exhaust.

If blue smoke then excessive oil consumption ; if black smoke then excessively rich mixture; and if white smoke

then steam in exhaust are expected.

Engine Exhaust Contains too much HC and CO.

The causes include ignition missing ; faulty air injection ; carburettor troubles ; incorrect ignition timing ;

defective catalytic converter ; and defective TCS system.

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