Starter Circuit Diagnosis

The Starter has two circuits , the Control Circuit and the Motor Circuit , to be able to diagnose the starter circuit successfully lets first take a thorough look at their components ,

Control Circuit:

• Ignition Switch.
• Neutral or Clutch safety switch.
• Sometimes a relay.
• (S) terminal on the Starter.
  

Motor Circuit:(also called Load or Battery Circuit)

• Battery positive cable, (Battery Positive to Starter B+).
• Solenoid magnetic switches, (B+ (Battery+) and M (Motor) Terminals).
• Battery Negative cable, (Starter M to Battery Negative).
  

Diagnosing the Control Circuit:
1.Pull the wire connected to the S Terminal on the starter.
2.Connect a Test-Lamp to it.
3.Crank the engine, the light should turn on.

If no electricity was detected (no light), the problem is in the control circuit, you should proceed to test the components backwards until you detect the faulty component.

If the light was detected at the (S) terminal wire the Control Circuit is fine, proceed to the Motor Circuit.

Diagnosing the Motor Circuit:

Diagnosing a Motor Circuit depends on the equipment you have, to do it professionally you should get a Battery And Starter System Tester, that can test the whole electrical system including the charging system. If you don't have access to such equipment a Digital Clamp Ammeter and a Voltmeter should do the trick.

1.Current Draw Test :

Current draw test can be done using a Clamp Ammeter , check the current in either the positive or negative Battery-to-Motor cables while cranking the engine , ignition should be disabled to be able to perform this test.
Different results should be expected from different engine types , below is a rough estimates on different engine types and maximum expected Amperes:

• 4Cylinder , Gas = 120 to 250 Ampere
• 6Cylinder and 8Cylinder , Gas = 250 Ampere
• 4Cylinder , Diesel = 350 Ampere
• 6Cylinder , Diesel = 450 Ampere
• 8Cylinder , Diesel = 650 Ampere
  

Draw Test Results :
High current draw could mean a bad starter-motor , or engine problems.
Low current draw could mean a high resistance issue in Battery-To-Motor cables.


2.Voltage-Drop Test:

If the Current Draw test resulted in low current, your next step would be a Voltage-Drop test, this test will detect high resistance in the Starter System. High resistance is caused by faulty cables, dirty contacts, or loose contacts.

Positive Cable Test:
Connect the Voltmeter's Positive to the Battery Positive and the Voltmeters Negative to Starter's B+ terminal, crank the engine, acceptable voltage drop should not exceed 0.4Volts.

Negative Cable Test:
Connect the Voltmeter's Positive to a clean spot on the Starter Housing and the Voltmeter's Negative to the Negative Battery terminal, crank the engine, acceptable voltage drop should not exceed 0.4Volts.

Back To No Crank Engine Fix

Mechanical Engine Damage Diagnosis

When diagnosing a no-crank or no-start situation, if the battery didn't show any problems, its better first to check for a mechanical engine problem(since cranking an engine with mechanical problem may worsen the case). lets go through the diagnosing steps:

1. Rotate Crankshaft By Hand: Try to rotate the crankshaft by hand two full rotations, if it rotated for two full rotations proceed to starter circuit diagnosis , else got to point 2.

   Rotating a crankshaft is not an easy process especially on a V8 engine

   
   
2. Hydrostatically locked engine: This occurs when a fluid has found its way to a cylinder in the compression phase ( through intake i.e while crossing a lake, or through a leaky head gasket), which will prevent the piston to move up, which will prevent the engine to complete its cycle, which will cause the engine to get hydrostatically locked. To Check and fix that: remove the spark plugs on all cylinders and crank it (30 seconds at most), if the engine cranked and started splashing fluid out of the sparkplug holes , you have successfully detected and fixed the problem , else proceed to next step .

   water is trapped between the valves and the piston , causing the engine to get locked

1. Faulty Belt-Driven Accessory: Belt-driven accessories (AC compressor, alternator... etc) could hold down the engine, to check if they are causing the problem, remove the accessories belt and try to crank the engine, if that didn't work proceed to next step.

   A Faulty alternator could lock the engine up

   
   
   
   
2. Loose Or Broken Timing Belt: In interference engines when the timing belt breaks or slips causing incorrect timing, the valves will collide with the pistons binding the valves or luckily just locking the engine, remove the timing belt cover and check for lost belt teeth or a loose belt.
3. Internal Engine Damage: If all above didn't work its an internal engine damage.

Proceed to : Starter Circuit Diagnosis
Back to : No Crank Engine Fix

Testing Car Battery

There are many different tests to check the battery's condition, the simplest is checking the voltage using a voltmeter, simply:

1. Connect the voltmeter positive to the battery positive terminal(not clamp) and voltmeter negative to battery negative terminal.(figure 1)

   Fig 1 : Battery terminal test

   
   











2. Although its acceptable to have at least 9.6v, recharge the battery until it reads 12v to 15v.
3. To check if the battery clamps are clean, repeat the test above on the battery clamps (figure 2) , the difference should be less than 0.1volts . If the difference is more than 0.1Volts , use a brush to clean the terminals and clamps using a mixture of baking soda and water , then rinse with water .

Fig 2 : Testing the battery clamps , the
difference should be less than 0.1Volt

Note on Multimeters : To check the battery using multimeter turn the knob to value close to 12v in the DC voltmeter section (20v in my case).

Note: Car batteries can become sulfated (sulfate coating lead plates) when undercharged, which make it a bad idea to place a load on the battery when the car is turned off.

Proceed to : Mechanical Engine Damage Diagnosis
Back to : No Crank Engine Fix

No Crank Engine fix

Early in the cold morning , holding your warm coffee mug , already late for work and rushing to your old but nice banger , admiring the car from angle view , hop in ,and twist the ignition key , NOTHING ! THE ENGINE IS NOT EVEN TURNING !



Your problem may be caused by:(click on links to go through diagnosis)

1. Battery.
2. Mechanical engine damage.
3. Starter circuit problem .

NOTE : Some cars won't start if the gear is not in Neutral or Park position , other cars may not start unless the clutch is pressed , please don't start taking your engine apart before trying these ;)