Diagnostic Test - Testing The Entire Fuel Injector Circuitry Using A Lab Scope (Preferred Method):
Testing fuel injectors with a lab scope can effectively test the entire electrical path for opens or high resistance. It can also help in determining if the fuel injectors pintle is mechanically sticking and not moving.
CONNECTING THE LAB SCOPE:
To effectively check the entire path, the scope should be connected to monitor the battery supply circuit voltage, fuel injector control circuit voltage, and current draw.
- Connect the scope lead from channel A to the battery supply voltage circuit.
- Connect the scope lead from channel B to the fuel injector control circuit.
- Connect the amp clamp from channel C to the battery supply voltage circuit.
Shown below is a typical fuel injector cycle broken into phases. It may be helpful to perform the same checks on another fuel injector and record for comparison. This can give a good reference for the expected current draw and inductive spike (kick) voltage range when analyzing the fuel injector being tested.
Below is a description of possible failure modes that can be detected during each phase:
- PHASE A - If battery voltage is not present on the fuel injector control circuit (channel B) with the fuel injector off it shows that the there is a blatant open in the path. If battery voltage is present on the battery supply circuit (channel A), it would indicate an open fuel injector coil.
- PHASE B/C
- This is where the driver is pulled and held low, energizing the fuel injector. If the voltage reading on the control circuit is not pulled near zero it would indicate resistance in the control circuit path (all of the voltage should be used up by the fuel injector). If the voltage drops low and then quickly ramps back toward battery voltage it could indicate that there is too much current flow and the driver was turned off for protection, or the LSD is failing. During phase C the current should build to peak amperage of approximately 1.0 amp if the circuitry is good.
- The voltage at the battery supply circuit (channel A) should remain constant throughout. If the supply voltage drops when the fuel injector is energized it would indicate resistance in the battery supply circuit.
- PHASE D - If resistance is detected in either of the circuits during the previous phases it can impact the inductive voltage spike when the fuel injector is turned off. This can also be seen in the amperage draw on the circuit. Higher resistance will reduce the amperage draw and inductive kick.
- PHASE E - If the voltage ramps down smoothly without the pintle bump it would indicate a stuck pintle inside the fuel injector.
- PHASE F - This is the same as Phase A. Fuel injector is off waiting for next actuation.