Small Engine Troubleshooting

Introduction(Source: Small Engines, R Bruce Radcliff)

Troubleshooting: The systematic elimination of the parts of a system or process to locate the malfunctioning

part(s).

Five keys to trouble shooting

1.Work systematically.2.Never make assumptions.3.Isolate the cause of the

problems as quickly as possible.4.Analyze all affected factors

related to the condition.5.Remedy the cause of the problem,

not just the effect.

Four (4) Troubleshooting Steps

InvestigationIsolationRemedyDocumentation

Troubleshooting Methods

Easy-likely

Split half

Quick check

Systems

Sequential

Easily-likely

1. ELM: isolates the cause of a malfunction by grouping possible causes as easy, difficult, likely and unlikely.

2. Once the possible causes have been grouped the problem is solved is sequence by identifying the easy-likely, easy-unlikely, difficult-likely and difficult-unlikely

3. Requires good understanding of engine systems and previous experience.

Easily-likely –cont. - Example

A riding lawn mower was used the previous season and stored for the winter. When the owner attempted to use it in the spring it could be cranked, but would not start.

No fuel Plugged carburetor

Bad plug Bad coil

Split Half

Split Half: isolates the cause of a malfunction by splitting the system into parts until the cause is isolated.

Split Half – cont. - Example

You are mowing grass with a self-propelled mower on a very hot summer day and stop for lunch. When you return the mower will not start. You check and find the tank has gas. What do you do?

Split Half – cont. - Example

Step one: Check for spark at the spark plug.

Good Spark

1. Fuel system2. Compression system

No or weak spark

Split electrical system into parts and check each part.Start with easiest. Spark plug

No spark

Split Half – cont. - Example

Step two: Remove spark plug from system.

Good Spark

Bad spark plug

No or weak spark

Check another electrical component.Stop switch/wire

No spark

Split Half – cont. - Example

Step three: Remove stop switch from system.

Good Spark

Bad stop switch

No or weak spark

Check another electrical component.Flywheel magnets

No spark

Split Half – cont. - Example

Step four: Polish magnet(s).

Good Spark

Engine runs.

No or weak spark

Check another electrical component.Ignition coil

Split Half – cont. - Example

Step five: Remove and test Coil.

Good coil

Check for unique problem such as shorted wire, etc.

No or weak spark

Replace coil

Note: coil must be tested with a special coil testing machine or with a multi meter.

Quick-check

• Isolates the cause of a malfunction by focusing on common problems identified by the manufacturer, product history, and/or service experience.

• May only be available to service personal.

Quick-check – cont. - Example

You go home for the weekend and are told that the last time the walk behind mower was being used the blade hit something and the engine died. No one can get it started.

Anyone that works with B & S engine driven lawn mowers know the they use an aluminum flywheel key that is designed to shear when the blade strikes an object.

When this occurs the ignition is out of time.

Quick check: flywheel key

Systems approach

Isolates problems by dividing the engine into separate systems and subsystems.

Five (5) common systems.1 Compression2 Fuel3 Electrical4 Cooling5 Lubrication

Symptom(s) of engine is traced to system and system parts.

Sequential method

Starts at one end of a system and tests all of the parts, in sequence, until the problem is found.

Sequential Method - Example

When trying to get an engine to start, your tests indicate the engine is not getting fuel to the combustion chamber.

Trouble shooting sequence.

1 Fuel tank

2 Fuel filter

3 Fuel lines

4 Carburetor

5 Intake valve

Summary

• The successful troubleshooter uses an analytical approach to trace the problem to the engine part or parts that are malfunctioning.

• Successful troubleshooters do not rely on any single method discussed in the textbook, but would develop their own system that would be a combination of all of these.