TROUBLESHOOTING IGNITION SYSTEMS

IN THIS SECTION, YOU WILL FIND THE FOLLOWING SUBSECTIONS:

TROUBLESHOOTING IGNITION SYSTEMS
TESTING FOR SPARK
PROBLEM OF NO SPARK
WEAK SPARK PROBLEMS
MISTIMED IGNITION SPARK

TROUBLESHOOTING IGNITION SYSTEMS

Troubleshooting procedures only performed when something clearly wrong with ignition system. First consideration whether or not there’s a spark, or consistent properly timed spark. Second consideration is if fuel being properly delivered. Spark, fuel, compression needed to allow engine to operate.

TESTING FOR SPARK

Several methods can be used to test to see whether ignition system producing spark. When engine won’t start, this is first troubleshooting test. Simplest method to disconnect spark plug wire. Then, holding wire with insulated pliers, place end of wire near engine block. Have second person turn over engine (by pulling starter cord or turning key). Spark should jump from end of plug wire to block.

If engine wasn’t starting but you get spark, plug may be bad, ignition timing off, or engine many not have ignition problem. Spark should be strong, sharp, bluewhite in color. If spark weak or yellow orange, may be ignition problem. If no spark appears, ignition system has problem. Most service manuals contain detailed troubleshooting procedures for ignition systems.

Ignition spark can be tested by using small test light. This tester a dual purpose test light. Spark created by high voltage passing through plug wire, through plug electrodes. This voltage can be measured with tester. If tester lead held near spark plug wire, high voltage in plug wire will induce voltage in tester. This induced voltage will cause bulb in tester to glow. Remember that this high voltage a shock hazard. Never place tip of tester on metal parts of ignition system. Never puncture spark plug wire with pointed tip of tester.

Timing light can also be used to check condition ignition system. Inexpensive timing light won’t require external voltage source. Timing light has two wire test leads. Remove spark plug wire from plug terminal. Connect one of light’s test leads to end of plug wire, other test lead to spark plug terminal. Turn engine over. Timing light’s bulb will flash each time light receives pulse of high voltage.

Other tools available to test for spark. Automotive timing light may be used. Must be connected to power source such as 12 volt DC battery in garden tractor or riding mower. Third lead from timing light clips onto spark plug cable. This an inductive pickup lead. High voltage cable will trigger timing light, create burst light from timing light bulb.

PROBLEM OF NO SPARK

Once determined ignition system isn’t producing spark, next step in troubleshooting will depend on type ignition system. If system uses points, points and condenser most likely cause no spark. To check, remove starter drive, flywheel, breaker points cover to examine points. Look for pitting, dirt, moisture between points contacts.

In some engines, points operated by plunger driven off crankshaft. Plunger passes through bushing in crankcase. Sometimes these bushings will wear, allow oil to seep past into points and condenser area. Remedy to remove points and condenser and clean area. Replace bushing, plunger rod, and install new points and condenser.

In electronic ignition system, problem of no spark may be caused by several factors. All simple to check. Check to make sure kill switch wire or grounding wire properly connected, not shorted out. Measure air gap for accurateness. If these appear good, problem probably failure in electronic module. Replace module with good component, and test engine. If engine still won’t start, flywheel key may be sheared or flywheel magnets lost magnetism. Remove flywheel to check these conditions.

In most engines, electronic modules inexpensive. Is a testing device used to test electronic modules, however is quite expensive and most small engine shops don’t have. Low cost replacement modules makes it easier simply to replace and test engine.

If electronic module faulty, remove blower housing and locate module. Next, remove module retaining bolts. With retaining bolts removed, can gently lift module away from mounting bracket. Install new module, but leave retaining bolts somewhat loose. Check magneto air gap with gap gauge, then tighten bolts to complete.

In battery ignition system, weak battery can cause no spark. Battery can be checked with voltmeter to see if proper voltage (approximately 12 volts) present. Ignition switch, safety interlock switches, safety interlock module can also cause no spark.

WEAK SPARK PROBLEMS

Weak spark can be caused by many factors. In points system, weal spark often caused by pitted or dirty points or faulty condenser. Can also be point gap that’s too large or too small. Faulty coil may also be problem.

In battery system, weak spark may be due to low battery voltage. Low voltage won’t allow proper magnetic fields to be created across primary and secondary windings of coil. Bad battery contacts, bad ignition switch contacts, faulty connection of any wire in ignition system can also cause weak spark.

In magneto system (including with electronic switching components), weak spark can be caused by weak flywheel magnets. Permanent magnets in flywheel rarely fail. Can lose magnetism over time or as result of impact to magnets (if flywheel hit or dropped say). Can test magnets by placing blade of large screwdriver about one inch from magnets. Should feel strong pull on blade of screwdriver. If pull weak, flywheel should be replaced.

Flaw in ignition module may cause weak spark. Best test method to simply replace module with known good module and try to start engine. Before condemning any ignition module, make sure is in proper position near flywheel, and that air gap proper width.

MISTIMED IGNITION SPARK

Mistimed ignition spark usually be noticed as hard to start or pinging engine. In breaker points system, point gap critical to timing. Point gap must be set to manufacturer’s specifications as given on engine plate or service manual.

On electronic systems, position of module near flywheel and width of air gap play important part in timing. Some older electronic ignition systems had slots in their armature coils that allowed both up and down and side to side motion. This type of coil is said to have both an air gap adjustment and an edge gap adjustment. In such an engine, the edge gap should be adjusted using the timing marks provided by the manufacturer.

Another possible problem that flywheel key has sheared. A partially sheared key will be bent, while a completely sheared key will be cut in half. A partially sheared key will cause the flywheel to be out of alignment with crankshaft, resulting in mistimed spark. Solution is to replace sheared key with new key. Partially sheared key will appear as if top and bottom sections of key offset from each other. Normal key will usually look like rectangular bar of metal. Best way to check condition of flywheel key to compare to picture in parts manual.