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. Q1. Q2. Q3. Q4. Q5. Q6. Q7. REVIEW  2  QUESTIONS What  are  the  three  types  of  pinion  drive mechanisms used on starting motors? What is the only function of a starter solenoid when it is mounted away from the starter? What is the most likely cause of a starter making a clicking sound? What type of starter uses gear reduction within the  starter  and  gear  reduction  between  the  drive pinion and the ring gear? When repairing a starter, you should replace the brushes if they are one half of their original size. (T/F) When   a   starter   is   being   tested   what   is   the maximum amount of time the engine should be cranked before starter damage can occur? 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