MOBILE OUTBOARD MECHANIC

Outboard engines need a strong spark to provide the heat required for ignition of the fuel.

Spark problems used to be very common but later model outboards very rarely develop ignition system faults.

Some later model outboards ignition systems require good battery voltage to develop good spark.

EFI outboards use computer software to carry out some spark testing.

A spark gap tester is required to put the ignition system under load.

A timing light is required to check spark condition and advance characteristics on some outboards.

To test spark output without the gap tester, the spark plugs are removed and fitted into the plug boots. The threaded ends are placed onto a metal part of the engine.

All spark plugs should be earthed. Running or cranking the outboard without the spark plugs earthed can cause component damage including ECM failure.

The engine is turned over as normal to start the outboard. The centre electrodes of the spark plugs at the threaded ends are observed.

There should be a strong blue spark visible. Shade is sometimes required in bright sunlight.

Normal precautions should be taken into consideration such as being aware of rotating parts of the engine, ensuring that there are no fuel leaks and keeping clear of the spark. Spark output can be up to 40,000 volts.

Ignition system diagnosis and repairs should only be carried out by competent persons to avoid possible injury or component damage.

Some spark related problems include:

- No Spark
- Weak Spark
- Intermittent Spark
- Sparking at the Wrong Time
- Cross Firing

No Spark:

If there is no spark, the test is done again with a known good spark plug in case there is a faulty spark plug.

If there is still no spark the next thing to check for is a faulty stop switch. The stop switch circuit is disconnected and the spark output is retested.

On small pull start outboards, the stop button is located and the two stop switch wires are followed back to where they originate. One goes to earth on the outboard and the other goes to the CDI. The wire that goes to the CDI is disconnected and spark is rechecked.

The condition of all the earths are checked as well as all the electrical connections and terminals related to the ignition system and the main harness plug. If these are dirty, loose or corroded, they may cause spark problems. They must all be clean and tight.

Other reasons for no spark could be failed flywheel magnets, faulty stator under the flywheel, faulty sensor coils under the flywheel, faulty capacitor discharge ignition unit (CDI), faulty capacitor discharge module (CDM) faulty microcomputer and faulty ignition coils.

There could be a combination of problems such a faulty stator that caused a CDI failure.

Most outboard ignition systems need a peak reading voltmeter to diagnose ignition system faults.

A standard voltmeter will not measure the ignition outputs properly.

Special ignition system test leads are often required to test ignition system components.

OEM ignition system specifications are required in order to determine the results of ignition system testing.

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Weak Spark:

The spark should be strong and blue. If it is slight and orange looking, the spark may be weak.

The spark output is put under load when it is in the combustion chamber under high heat and high pressure conditions. A weak spark may not spark when under these conditions.

Weak spark may cause starting and running difficulties as there may not be enough heat generated in the spark to accomplish ignition of the fuel/air mix in the combustion chamber.

Common reasons for weak spark are faulty flywheel magnets and faulty stator.

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Intermittent Spark:

Sometimes the spark is there and sometimes it is not. These are a real problem as, unless the failure happens when the diagnosis is being performed or if there are tell-tale signs such as melted insulation, they are very difficult to diagnose with any sort of certainty.

Some ignition system components consist of many windings of insulated copper wire. This insulated copper wire can fail and create an open circuit, short circuit or a leak to earth when the engine is hot and then be normal when the engine cools.

The CDI and CDM consist of many electronic components and these can fail at any time without notice and then come good again.

An intermittent ignition system fault can be repaired confidently by replacing all components but this can be very expensive and possibly unnecessary.

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Sparking at the Wrong Time:

Incorrect ignition timing can cause piston failure. This can be caused by a faulty CDI, faulty trigger coils, a sheared flywheel key or incorrect timing set up.

The flywheel may have to be indexed to diagnose this fault.

If all cylinders are out of timing it is likely to be the flywheel key. Ignition timing should be checked when the outboard is serviced.

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Cross Firing:

On multi cylinder engines, the spark might be crossfiring into the wrong cylinder and cause possible backfiring. This is not common but does happen.

The spark plugs' leads should be inspected thoroughly and positioned away from each other

The flywheel may have to be indexed to diagnose this fault.

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