Day 14 - Petrol Fuel Injector Testing and Primary & Secondary Ignition Patterns

Petrol Fuel Injector testing

Make: Lexus
Model: ES300

1. Listen to the injectors as the engine idling. Use stethoscope, vacuum line or long screwdriver.

Sound like a sharp tap? Yes
Can you get to all the injectors? Yes










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.

Battery voltage: 14.23V

Voltage at each injector
Cyl#2: 14.13V
Cyl#4: 14.13V
Cyl#6: 14.13V

3. With engine idling, watch injector firing by using an LED tester or test light.

Testing with Toyota 4A-FE
4. With engine idling, watch injector firing by using a multimeter set to read %(duly cycle).
Cyl#1: 5.0%
Cyl#2: 5.0%
Cyl#3: 5.0%
Cyl#4: 5.0%

5. With the multimeter still set to read %(duly cycle), accelerate the engine with short, fast throttle openings and note maximum % reading you can get on the multimeter.
Cyl#1: 15.5%
Cyl#2: 15.5%
Cyl#3: 15.5%
Cyl#4: 15.5%

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

Cyl#2: 32Hz
Cyl#4: 32Hz
Cyl#6: 32Hz

Formula to calculate the pulse width of each injector
Pulse width ms  = (duty cylce / 100) / Frequency kHz

Cyl#1: (5.0 / 100) / 0.032 = 1.56ms

Primary & Secondary Ignition Patterns

Make: Toyota
Model: 4A-FE

1. Labscaope setting

Coil wire on top of the distributor cap

number 1 spark plug connection

negative side of the ignition coil

2. Primary Voltage Patterns



	Cyl 1	Cyl 2	Cyl 3	Cyl 4
Firing Voltage(A)	over 300V	over 300V	over 300V	over 300V
Burn Voltage(B)	50V	50V	50V	50V
Dwell Time(C)	6.7ms	6.7ms	6.7ms	6.7ms
Burn Time(D)	1.3ms	1.3ms	1.3ms	1.3ms

The cylinders are displayed from left to right by firing order. By having a parade display, the signals can be compared with one another.

Raster is the best scope position to view the spark lines of all the cylinders to check for differences.(spark line length and transistor-on point) Cylinder #1 appears at the bottom of the screen and all other cylinder patterns are displayed upward in the engine's firing order.

Burn time is usually more reliable than KV firing voltage so it can be used for diagnosis.

3. Secondary Voltage Patterns

	Cyl 1	Cyl 2	Cyl 3	Cyl 4
Firing Voltage	5.0kV	4.0kV	5.0kV	5.0kV
Burn Time	1.4ms	1.3ms	1.4ms	1.5ms
Snap Acceleration	12kV	12kV	12kV	12kV

The height of the firing voltage should be between 5kV and 15 kV with not more than a 3kV difference between highest and the lowest cylinder's firing voltage.
Following are guidelines for spark line lenght(Burn time):
0.8 ms : too short
1.5 ms : average
2.2 ms : too long



Disconnect one spark plug wire(Cyl #3) and short to the engine with a jumper wire. Start the engine and let it idle.

	Cyl 1	Cyl 2	Cyl 3	Cyl 4
Firing Voltage	5.0kV	5.0kV	3.0kV	5.0kV
Burn Time	1.4ms	1.3ms	1.9ms	1.5ms

This spark plug has a long burn time comparing with other cylinders due to a grounded plug wire. Less energy is used to fire the spark plug, the burn time was longer.

There is no a spark tester. So we could not do some experiments. Instead some theories are put here.

If the spark line is too short, possible causes include the following:

1. Spark plugs gapped too widely

2. Worn cap or rotor

3. High-resistance spark plug wire

4. Air-fuel mixture too lean

If the spark line is too long, possible causes include the following:

1. Fouled spark plugs

2. Spark plugs gapped too closely

3. Shorted spark plug or spark plug wire