WS1 - Petrol Fuel Injector Testing

Petrol Fuel Injector Testing
1. Listen to the injectors as the engine is idling. Use stethoscope, vacuum line or long screwdriver. Be careful of moving parts. They should sound like a sharp tap, not a dull thud or nothing.
  This is a crude test to see if they are being actuated and are opening.

All injectors are OK.

2. Check voltage to the injectors when idling or key on. This makes sure you have battery voltage to the injectors so they can work.

Record battery voltage: 14.17V

Record voltage at each injector you can get to by back probing.

Cylinder	1	2	3	4
Voltage ( V )	14.03	14.04	14.04	14.04

3. With engine idling, watch injector firing by using an LED tester or test light. Hook up test light and connect tip to pin that has back probed connector to injector. As the injector is grounded by the ECM to fire, the test light should also be grounded to fire, and will flash.

All injectors are working fine.

4. With engine idling, watch injector firing by using a multimeter set to read % (duty cycle). Record the readings for each cylinder at idle in the boxes below.

Cylinder	1	2	3	4
Duty cycle  ( % )	78.5	79.3	78.7	78.6

5. With the multimeter still set to read % (duty cycle), accelerate the engine with short, fast throttle openings (don't over-rev or damage the engine please), and note in the boxes below the maximum % reading you can get on the multimeter: note the RPM.

Cylinder	1	2	3	4
Duty Cycle ( % )	88.0	88.0	88.7	88.1

6. Set the multimeter to read Hz, and with the engine idling, record the reading for each cylinder in the boxes below:

Cylinder	1	2	3	4
Hz	192	182	217	179

7. With the multimeter still set to read Hz, increase the engine RPM, and watch how the Hz changes. Record your highest reading in the boxes below.

Cylinder	1	2	3	4
Hz	527	433	431	455

Using this formula calculate the pulse width of each injector both at idle and when the engine is revved up

“pulse width ms = (% Duty cycle/100) / Frequency”

Idle:

1. 78.5 / 100 / 192 = 4.1ms

2. 79.3 / 100 / 182 = 4.4ms

3. 78.7 / 100 / 217 = 3.6ms

4. 78.6 / 100 / 179 = 4.4ms

Cylinder	1	2	3	4
Time at idle ( ms )	4.1	4.4	3.6	4.4

Revved:

1. 88 / 100 / 527 = 1.7ms

2. 88 / 100 / 433 = 2ms

3. 88.7 / 100 / 431 = 2.1ms

4. 88.1 / 100 / 455 = 1.9ms

Cylinder	1	2	3	4
Time when revved ( ms )	1.7	2	2.1	1.9

When acceleration, the ECU gives the signal to grounded the injector and let it open longer, to spray more fuel for the burn and gives the more power to drive the engine run faster, increase the RPM.