Using a voltmeter, connect the leads to the positive terminal of the battery and the starting motor output terminal.

With the ignition or injection system disabled, crank the engine. Note the voltmeter reading. It should not be over 0.5 volts. If voltage drop is greater, something within the circuit has excessive resistance. There may be a burned or pitted solenoid contact, loose electrical connections, or other malfunctions. Each component is then to be tested individually.

STARTER GROUND CIRCUIT TEST. - The starter ground circuit test checks the circuit between the starting motor and the negative terminal of the battery.

Using a voltmeter, connect the leads to the negative terminal of the battery and to the end frame of the starting motor. Crank the engine and note the voltmeter reading. If it is higher than 0.5 volts, check the voltage drop across the negative battery cable. The engine may not be properly grounded. Clean, tighten, or replace the battery cable if needed. A battery cable problem can produce symptoms similar to a dead battery, bad solenoid, or weak starting motor. If the cables do NOT allow enough current to flow, the starter will turn slowly or not at all.

REVIEW 2 QUESTIONS

Q1. What are the three types of pinion drive mechanisms used on starting motors?

Q2. What is the only function of a starter solenoid when it is mounted away from the starter?

Q3. What is the most likely cause of a starter making a clicking sound?

Q4. What type of starter uses gear reduction within the starter and gear reduction between the drive pinion and the ring gear?

Q5. When repairing a starter, you should replace the brushes if they are one half of their original size. (T/F)

Q6. When a starter is being tested what is the maximum amount of time the engine should be cranked before starter damage can occur?

Q7. What test is used to check for excessive resistance in all components between the positive battery terminal and the starter?

IGNITION CIRCUIT

Learning Objective: Identify ignition-circuit components, their functions, and maintenance procedures.

The ignition circuit supplies high voltage surges (some as high as 50,000 volts in electronic ignition circuits) to the spark plugs in the engine cylinders. These surges produce electric sparks across the spark plug gaps. The heat from the spark ignites the compressed air-fuel mixture in the combustion chambers. When the engine is idling, the spark appears at the spark plug gap just as the piston nears top dead center (TDC) on the compression stroke. When the engine is operating at higher speeds, the spark is advanced. It is moved ahead and occurs earlier in the compression stroke. This design gives the compressed mixture more time to bum and deliver its energy to the pistons.

The functions of an ignition circuit are as follows:

Provide a method of turning the ignition circuit ON and OFF.

Be capable of operating on various supply voltages (battery or alternator voltage).

Produce a high voltage arc at the spark plug electrodes to start combustion.

Distribute high voltage pulses to each spark plug in the correct sequence.

Time the spark so that it occurs as the piston nears TDC on the compression stroke.

Vary spark timing with engine speed, load, and other conditions.

PRIMARY AND SECONDARY CIRCUITS

The ignition circuit is actually made of two separate circuits which work together to cause the electric spark at the spark plugs. These two circuits are the PRIMARY and SECONDARY.

The primary circuit of the ignition circuit includes all of the components and wiring operating on low voltage (battery or alternator voltage). Wiring in the primary circuit uses conventional wire, similar to the wire used in other electrical circuits on the vehicle.

The secondary circuit of the ignition circuit is the high voltage section. It consists of the wire and components between the coil output and the spark plug ground. Wiring in the secondary circuit must have a thicker insulation than that of the primary circuit to prevent leaking (arcing) of the high voltage. 2-31