Diagnosing engine problems on the Ford Falcon XK six-cylinder engine requires a systematic approach. The following troubleshooting guide outlines common symptoms and their likely causes within the starting, ignition, fuel, cooling and mechanical systems. By identifying the specific symptom first, the technician can narrow down the likely source of the fault and carry out targeted inspection and repairs.
Engine Will Not Crank
When the engine fails to crank, the cause is usually related to the starting system. If the starting system is not at fault, the engine may be suffering from hydrostatic lock or internal seizure.
Removing the spark plugs and attempting to crank the engine can help determine whether coolant or fuel has entered the cylinders. If the engine turns with the plugs removed, the problem may be caused by liquid inside the combustion chambers. In this case the cylinder head gasket, cylinder head and engine block should be inspected for cracks or internal leakage.
Engine Cranks Normally but Will Not Start
If the engine turns over normally but does not start, the problem usually lies within either the ignition system or fuel system.
The first step is to confirm that fuel is present in the tank. If sufficient fuel is available, the ignition system should be checked by testing spark intensity at each spark plug wire.
Disconnect a spark plug wire and attach a suitable test adapter. Hold the adapter approximately 3/16 inch from the exhaust manifold and crank the engine.
No Spark or Weak Spark at the Spark Plugs
If no spark is present at the spark plugs, the fault is likely in the ignition system.
To determine whether the fault lies in the primary or secondary ignition circuit, remove the coil high-tension lead from the distributor and hold it approximately 3/16 inch from the cylinder head while cranking the engine.
If spark is present at the coil lead but not at the plugs, the fault is likely in the distributor cap, rotor or spark plug wires.
If no spark appears at the coil lead, the problem is probably within the primary ignition circuit, coil, or wiring between the coil and distributor.
Good Spark at the Spark Plugs
If spark is present and strong at the spark plugs, the ignition system is likely functioning correctly. The next step is to check the fuel system and choke operation.
The choke linkage should be inspected for binding or damage. The choke plate should close when the choke control is pulled out and open fully when the control is pushed in.
Fuel delivery can be tested by operating the throttle manually. Each throttle movement should produce a visible squirt of fuel from the accelerator pump discharge nozzle.
If fuel is delivered correctly, the engine may be flooded or may have an internal mechanical problem such as faulty valves or low compression.
If no fuel is discharged, disconnect the fuel line at the carburetor and crank the engine to check fuel flow. If fuel is not reaching the carburetor, inspect:
The fuel pump
The fuel filter
Fuel lines for blockage
Collapsed flexible fuel lines
Blocked fuel tank vent
If fuel is reaching the carburetor, the carburetor float system, needle and seat assembly should be checked for proper operation.
Engine Starts but Fails to Keep Running
If the engine starts but stalls shortly afterward, the problem usually involves fuel mixture or idle system adjustment.
Possible causes include:
Improper idle fuel mixture adjustment
Engine idle speed set too low
Choke not operating correctly
Incorrect carburetor float setting
Faults within the fuel inlet system
Contamination such as dirt or water within the fuel system may also cause stalling. Carburetor icing or a defective fuel pump can also contribute to this condition.
Electrical causes may include incorrect breaker point adjustment, defective spark plugs or high-tension wiring leakage.
Engine Runs but Misses
Engine misfire can occur either steadily or intermittently. Determining whether the miss is steady or erratic and whether it occurs under load or at idle will help isolate the cause.
Misses Steadily at All Speeds
A steady miss can be isolated by removing each spark plug wire individually while the engine is running. If removing a wire causes no change in engine speed, that cylinder may not be contributing power.
Possible causes include ignition faults such as:
Defective spark plug
Distributor cap fault
Ignition wiring failure
If ignition components are functioning correctly, the engine should be tested for low compression or internal mechanical faults.
Misses Erratically at All Speeds
Erratic misfiring may be caused by:
Restricted exhaust system
Incorrect breaker point adjustment
Defective condenser or ignition coil
Faulty secondary ignition wiring
Misses at Idle Only
When a miss occurs only at idle speed, common causes include:
Improper idle mixture adjustment
Defective ignition components
Excessive wear in the distributor shaft
Worn distributor cam
Vacuum leaks or faults within the vacuum booster pump may also contribute to irregular idle operation.
Misses at High Speed Only
Misfire occurring only at high speed may indicate fuel delivery problems such as:
Clogged power valve
Low or irregular fuel pump pressure
Restricted fuel inlet system
Engine overheating can also contribute to high-speed misfire conditions.
Rough Engine Idle
A rough idle condition is commonly caused by improper carburetor adjustment or vacuum leakage.
Typical causes include:
Idle mixture incorrectly adjusted
Float setting incorrect
Air leaks between carburetor and intake manifold
Restricted carburetor passages
Fuel bleeding from the accelerator pump discharge nozzle
Throttle plate not closing completely
Ignition faults may also contribute to rough idle, including improperly adjusted breaker points, fouled spark plugs or incorrect ignition timing.
Loose engine mountings or incorrect valve lash adjustment may also cause rough running at idle speeds.
Poor Acceleration
Poor acceleration may result from faults in the ignition system, fuel system or transmission.
Possible ignition system causes include:
Incorrect ignition timing
Worn or incorrectly adjusted breaker points
Faulty spark plugs
Distributor advance mechanism not functioning correctly
Fuel system problems may include:
Defective accelerator pump
Blocked accelerator pump check valves
Damaged pump diaphragm
Restricted passages in the carburetor
Transmission issues such as clutch slippage or improper band adjustment (on Fordomatic transmissions) may also reduce acceleration performance.
Excessive Fuel Consumption
If fuel consumption is unusually high, the actual fuel usage should first be verified using proper testing equipment.
If excessive fuel consumption is confirmed, possible causes include:
Incorrect carburetor adjustment
Improper float level
Blocked air cleaner
Worn carburetor jets
Accelerator pump discharge problems
Ignition timing incorrect
Spark plug condition or adjustment incorrect
Faulty distributor spark advance mechanism
Engine mechanical faults such as low compression or camshaft wear may also contribute to poor fuel economy.
Engine Overheats
Engine overheating may result from cooling system faults, ignition problems or mechanical engine issues.
Cooling system causes include:
Low coolant level
Cooling system leaks
Loose or slipping drive belt
Blocked radiator fins
Defective thermostat
Blocked coolant passages
Inoperative water pump
Ignition timing that is set incorrectly may also cause overheating.
Mechanical faults such as loose cylinder head bolts, incorrect valve lash or improper oil viscosity may contribute to excessive engine temperature.
Loss of Coolant
Loss of coolant usually indicates leakage within the cooling system or engine.
Possible cooling system causes include:
Leaking radiator
Loose or damaged hose connections
Water pump leakage
Defective radiator cap
Overheating
Engine-related causes may include:
Defective cylinder head gasket
Incorrect cylinder head bolt tightening
Leaking cylinder block core plugs
Faulty temperature sending unit
Cracked cylinder head or block
Warped gasket sealing surfaces
Safety, Copyright and Source Notice
Safety Disclaimer
Working on motor vehicles involves mechanical, electrical and chemical hazards. Always ensure the vehicle is safely supported, the engine is switched off when appropriate, and suitable safety equipment such as gloves and eye protection is used. If you are unsure about any repair or maintenance procedure, consult a qualified mechanic before attempting the work.
Source
Information compiled from period factory service literature.
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