Scope Of Application; Use Of The Cpu 95 Ignition Unit Diagnosis Capability - Kohler SFGLD480 Operation & Maintenance Manual

1. INTRODUCTION
This document describes the various methods for detecting spark plug failure to set usable criteria for
determining when the spark plugs in the engine should be replaced.

2. SCOPE OF APPLICATION

Fuel:
Spark plugs:
Coils:
High voltage ignition leads:
Extenders:
Any change to the spark plug, wire or coil may involve a change to the values used in this document.
Either criterion can be used depending on the engine's ignition system.

3. USE OF THE CPU 95 IGNITION UNIT DIAGNOSIS CAPABILITY

There are values in the CPU 95 for the voltage needed to produce a spark in each of the engine's spark plugs
with a dimensionless number called the "spark plug reference voltage." Its usefulness lies in how it changes
according to spark plug wear.
The reference values in the CPU95 increase as the electrodes wear. High values mean greater electrode wear.
These values can be used as a reference to determine when the spark plugs fail.
The "spark plug reference voltage" value has an initial value which basically depends on the coil used, but may
also vary according to the types of wires and spark plugs.
This value is typically about 100 when the spark plug is new and increases as the spark plug wears (its gap
growing wider). This "spark plug reference voltage" increases slowly to values of nearly 130 – 135, above which
the spark loses consistency, causing misfiring in the engine.
There is a maximum CAVG (average cylinder value) value above which the CPU 95 issues a HI SPARK VOLT
warning to replace the spark plugs.
There are other limits in the CPU-95 for detecting problems in a specific cylinder:
Minimum CAVG (average cylinder value) limit: most probably due to a short circuit in the spark plug
-
(centre electrode and ground joined). In this case, readjust the gap.
- Difference between the EAVG (average engine value) and CAVG (average cylinder value) readings. If the
difference is much less than the EAVG value, this may be due to a short circuit in the spark plug in that
cylinder. If the difference is greater, this may be the result of too large a gap or a fault in the spark plug
lead. In the event of a fault in the spark plug, readjust the gap or change the spark plug. If the fault is in
the spark plug lead, replace the lead.
PRODUCT INFORMATION
IO-G-M-33-002e
CONVENTIONAL SPARK PLUG REPLACEMENT CRITERIA IN
Gas
Spark plugs without prechamber (4 electrodes, J-type, circular electrode, etc).
See IO-G-M-33-007e: Spark plug maintenance. Overview.
INDEX
F
GAS ENGINES
5.2.27
DATE
Dep. 2
May 2016
O&M_2.002211.810_A_10_2016
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