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
- Valve Timing

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.

In a distributorless ignition system, problems with the primary system are the usual cause of a no-start condition. Failure of an individual ignition coil or ignition cable may cause severe driveablity issues but the engine will normally still start.

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. Ignition Switch
- 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.
- 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.

Testing
- For detailed information on testing, see Ignition System. Ignition System

WARNING: Distributorless Ignition Systems develop extremely high voltages. Only trained technicians should test these systems.

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 fuel injectors are not opening.

Testing
- Check Fuel Pressure, verify there is fuel in the tank.
- Verify the Fuel Pressure Regulator is operating properly. Fuel Pressure Regulator
- Verify the Fuel Pump Relay is operating properly. Fuel Pump
- Verify the Fuel Injector is receiving an opening signal.

NOTE: The fuel injection system requires a reference signal from the Ignition system for proper operation. An Ignition system problem may prevent the fuel injection system from operating. Ignition System

Not Enough Fuel
A rich air/fuel mixture is required for cold starts. The fuel control system compensates by adding additional fuel.

Testing
- Check fuel pressure. Low pressure will cause cold starting problems.
- Check for proper fuel control, see Computers and Control Systems. Computers and Control Systems
- 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
- Check fuel pressure. High pressure will cause warm starting problems.
- Remove vacuum hose from the fuel pressure regulator and verify the diaphragm is not leaking.
- Check for proper fuel control, see Computers and Control Systems. Computers and Control Systems

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

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