Cranks, Won't Start

CRANKS, WON'T START

Description
The starter will engage, and the engine will crank, but it will not start.

Explanation
Four primary elements are required for proper engine starting:
- Spark
- Fuel
- Compression
- Timing (Valve and Ignition)

Spark
The ignition system provides the spark required to ignite the air/fuel mixture. The ignition system is made up of two subsystems, the primary and the secondary.

The primary ignition system triggers the spark, while the secondary ignition system distributes the spark to the individual cylinders.

Primary Ignition System
A failure of any one component in the primary ignition system may result in a no-start condition. The primary system is composed of:
- Ignition Switch - Provides power to the primary side of the ignition coil. Steering Column
- Ignition Coil Primary Windings - The primary windings of the ignition coil are used to create the primary electric field within coil. The buildup and collapse of the primary field is what generates the spark output voltage in the secondary windings of the ignition coil. Ignition Coil
- Pickup Coil - Used for initiating the spark. The pickup coil sends a signal to the ignition control module, telling it when to trigger the spark. Pick-Up Coil
- Ignition Control Module - Used as an On/Off switch to control power to the primary windings of the ignition coil. The ignition control module turns the ignition coil primary ground circuit "ON" and "OFF" to build up and collapse the primary field. Ignition Control Module

Secondary Ignition System
A failure of a secondary ignition component does not always lead to a no-start condition. The secondary system only distributes the spark, for a no-start condition to occur a component common to all cylinders must fail. Secondary components which may cause a no-start condition are:
- Ignition Coil Secondary Windings - The secondary windings develop the high voltage which is necessary to initiate the spark.
- Ignition Coil Wire - The coil wire transfers the secondary voltage of the coil to the distributor.
- Distributor Rotor - The rotor distributes the secondary voltage to the individual terminals on the distributor cap.
- Distributor Cap - The cap distributes the secondary voltage to each of the individual ignition cables and spark plugs.

Testing
- With the key "ON" and the engine "OFF", verify the ignition coil positive terminal is receiving 12.0 V.
- With the key "OFF", inspect the coil wire and check for high resistance or evidence of arcing or burning.
- Inspect the distributor, verify the rotor is undamaged and that all components are completely dry.
- For detailed information on testing, see Ignition System. Ignition System

Fuel
Starting a cold engine requires a rich mixture, while starting a hot engine does not. If the fuel system does not deliver the correct amount of fuel for the current conditions the engine may not start.

Causes
No Fuel
The Fuel pump is not operating or the Carburetor is not delivering fuel to the incoming air.

Testing
- Check Fuel Pressure, verify there is fuel in the tank.
- While cycling the throttle valve, check that the accelerator pump injects fuel into the throat of the carburetor (this verifies that fuel is reaching the carburetor bowl).

Not Enough Fuel
A rich air/fuel mixture is required for cold starts. The choke is used to temporarily richen the mixture while the engine warms up.

Testing
- With the engine cold, cycle the throttle valve and verify the choke plate shuts.
- While cycling the throttle valve, verify the accelerator pump operates.
- Inspect all vacuum lines for proper routing or signs of leakage. Diagrams

Too Much Fuel
Warm engines require a leaner mixture than cold engines. Excessive fuel may richen the air/fuel mixture to the point where it will not ignite. The spark plugs may become fuel or carbon fouled.

Testing
- Apply vacuum to the choke unloader and verify that the choke opens slightly.
- Verify that fuel is not overflowing from carburetor bowl vent or venturis (from a stuck open needle valve).
- Attempt to start the vehicle with the choke blocked open. If the vehicle starts, the air/fuel mixture is too rich.

Compression
For a compression problem to cause a no-start condition, multiple cylinders must be involved. Low compression in only one or two cylinders will not normally prevent an engine from starting. Low compression on all cylinders may be caused by:
- Broken Timing Chain - Prevents camshaft rotation and valve movement.
- Broken Crankshaft - Prevents piston and timing chain rotation.
- Camshaft/Crankshaft Alignment - If the camshaft and crankshaft are not properly aligned, the intake and exhaust valves will not open and close at the proper times.
- Bent Valves - Intake or exhaust valves which have been damaged/bent by over-revving or a broken timing chain will prevent compression from developing.

Testing
- Perform Compression Check.
- Verify Timing Chain is intact and aligned properly. Timing Components

Timing (Valve or Ignition)

Ignition Timing
Ignition timing which is excessively advanced or retarded may result in a no-start condition. If the timing is advanced, the engine will be difficult to crank and rotation will tend to stop rapidly. If the timing is retarded the engine will have a distinctive low and dull sound while attempting to start.

Testing
- Check Ignition Timing and adjust as necessary.

Valve Timing
Incorrect valve timing will result in low compression across all cylinders. The valves may remain open during the compression stroke or closed during the exhaust and intake strokes.

Testing
- Perform Compression Check.
- Check Timing Chain alignment. Timing Components