ASE4 Ignition System Diagnosis and Repair 3

Question 1

A spark plug gap measures 0.065 inches; specification is 0.040 inches. The effect on ignition will be:

Accepted Answer

Higher voltage demand that may cause misfires

Answer

A gap larger than specification requires more voltage to bridge, which can exceed coil capacity and cause misfires.

Question 2

During an ignition coil primary voltage test with a lab scope, the technician sees no voltage drop across the coil. This indicates:

Accepted Answer

The coil driver transistor or ECM output is not switching

Answer

No primary voltage drop means the coil is not being triggered by the ECM driver, pointing to a control circuit fault.

Question 3

A technician observes crossfire between two adjacent ignition wires. The MOST likely cause is:

Accepted Answer

Wires routed too closely together or damaged insulation

Answer

Crossfire occurs when high-voltage wires are routed parallel and close together, allowing inductive energy to jump to an adjacent wire.

Question 4

What does a long spark line on an ignition oscilloscope pattern indicate?

Accepted Answer

High resistance in the secondary circuit

Answer

A long, high-voltage spark line indicates high resistance in the secondary circuit, which the coil must overcome to sustain the arc.

Question 5

An intermittent misfire code P0301 is stored but no misfire occurs at idle. The BEST next step is:

Accepted Answer

Road-test the vehicle under the conditions that set the code

Answer

Since the misfire is intermittent and load-dependent, reproducing it under the same conditions is required before replacing parts.

ASE4 - ASE Automobile Engine Performance Practice Test