Further Fault Patterns With Evaluation

WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 2003 BMW 540i, 2002 BMW 540i, 2001 BMW 540i, 2000 BMW 540i, and 1999 BMW 540i. However, it is still accessible from the selected car via links, so may be relevant.

Evaluation of sparking period and ignition voltage peaks at idling speed:

Normal combustion period.
Normal ignition voltage peak. Ignition system is OK.

Fig 1: Evaluation Of Sparking Period & Ignition Voltage Peaks At Idle Speed

Courtesy of BMW OF NORTH AMERICA, INC.

Long sparking period (1) with low ignition voltage peak (2). Indicates low compression.

Fluctuating sparking period: Indicates contamination on spark plug (shunt).

Fig 2: Long Sparking Period With Low Ignition Voltage Peak

Courtesy of BMW OF NORTH AMERICA, INC.

Short sparking period (1) with high ignition voltage peak. Constant but short sparking period: Indicates defective ignition lead.

Fig 3: Short Sparking Period With High Ignition Voltage Peak

Courtesy of BMW OF NORTH AMERICA, INC.

NOTE: The sparking-voltage line could sometimes be missing completely and the ignition voltage peak could rise very high.

IGNITION VOLTAGE TOO HIGH

Electrode Gap	Large
Compression	High
Fuel Air Mixture	Lean
Electrode Temperature	Low
Electrode Condition	Burnt
Ignition Lead	Interrupted

IGNITION VOLTAGE TOO LOW

Electrode Gap	Small
Compression	Low
Fuel Air Mixture	Correct
Electrode Temperature	High
Electrode Condition	New