Hard Starting, Excessive Cranking

HARD STARTING, EXCESSIVE CRANKING

Description
The engine will start, but not easily. The starter operates satisfactorily but numerous revolutions or attempts are required before the engine starts.

Explanation
For an engine to start quickly and easily the following need to be present:
- Ignition Spark
- Correct Air/Fuel Mixture
- Proper Ignition Timing
Any one of the above which is incorrect could lead to hard starting and excessive cranking.

Possible Causes

Weak Spark
During start-up, a very rich Air/Fuel Mixture is needed. To properly ignite this mixture a strong spark is required.

A vehicle with a weak spark exhibits many symptoms similar to a flooded engine. If the ignition spark is too weak the spark, plugs may become fuel fouled, resulting in extremely long cranking times. When the vehicle starts, only one or two cylinders may be firing initially. The remaining cylinders will slowly begin to fire as engine speed increases.

The weak spark may be the result of the following:
- Weak Coil. Insulation break down within the coil or a build up of resistance in the coil windings can greatly reduce the voltage output of the coil. Ignition Coil
- Bad Ground or Power to the Coil Primary Circuit. A small reduction in the voltage input to the coil primary windings can result in a very large voltage decrease in the secondary output windings.
- High Secondary Resistance. High resistances in the Ignition Cables or distributor cap and rotor can greatly reduce the strength of the spark at the spark plugs.
- Insulation Breakdown. Weak insulation along the ignition cables or within the distributor cap can allow ignition voltage to leak out and short to ground.
- Defective Ignition Module. A weak primary signal from the Ignition module will reduce the ignition coil output. Ignition Control Module

Testing
- Visually inspect the ignition system for insulation breakdown, arcing, and corroded terminals.
- Using an Ignition Scope or Spark Tester, check the ignition spark. If a spark tester is used, the spark should be blue and thick. A weak spark will be orange/yellow and thin.

Incorrect Air/Fuel Mixture
A mixture which is either too lean or too rich can cause hard starting problems. A mixture which is too lean will not readily ignite and a mixture which is too rich may foul the spark plugs.

Incorrect Air/Fuel Mixture during starting can be caused by:
- Fuel control problem.
- Vacuum leaks.

Testing
- Visually inspect all vacuum lines, intake hoses, and brake booster hose for evidence of leakage or wear. Diagrams
- Inspect the PCV valve and verify its operation. A PCV valve which is stuck open may act as a vacuum leak and cause a lean Air/Fuel Mixture. Positive Crankcase Ventilation
- Using a propane enrichment tool, enrich the mixture with a small amount of propane. If the engines starts easily, the mixture is too lean.

WARNING: Propane enrichment is highly flammable and should only be attempted by experienced professional mechanics.

- Visually inspect the spark plugs. If the spark plugs are wet with fuel or are carbon fouled, the mixture may be too rich. Check the fuel control system. Computers and Control Systems

Retarded Ignition Timing
Retarded timing will result in hard starting (may die after starting) and an overall loss of power. The exhaust will have a distinctive dull and low sound.

Testing
- Check Ignition Timing and adjust as necessary.

Weak/Low Compression
An engine with low compression may require excessive cranking (especially when cold) to start. Worn rings or valves may significantly lower compression.

Testing
- Perform a Compression Check.

NOTE: If compression is initially low, inject a teaspoon of oil into each cylinder and repeat the test. If the compression increases, the rings are worn.

- If one or more cylinders still indicate low compression, perform a cylinder leakdown check to determine the cause.

NOTE: A cylinder leakdown check utilizes regulated, compressed air to pressurize each cylinder (at Top Dead Center Compression). While performing this check, the cause of the compression leak may be determined by listening for escaping air:
- Air heard leaking from the exhaust indicates an exhaust valve problem
- Air heard leaking from the intake or throttle body indicates an intake valve problem.
- Air heard leaking from the PCV valve or PCV breather hose indicates a piston, ring, or cylinder wall problem.
- Air heard leaking from an adjacent cylinder indicates a head gasket failure between the two cylinders (both adjacent cylinders will have identically low compression).
- Air seen bubbling out of the radiator indicates a head gasket failure (or a cracked head/block).