User Manual

Page7
5. MEASURING MODES
There are four different ignition system parameters that can be selected for
measurement,dependingontheengine’signitionsystem:
•EngineRPM.
•Sparkburn(ring)time.
•Sparkplugvoltage.
•Dwellangles(forignitionsystemsequippedwithhighvoltagesparkplugwires).
• Primaryignitioncoilcurrentramptime(forcoilonplugandcoilnearplugignitionsystems).
5.1 Engine RPM
MeasuresengineRPM(revolutionsperminute)in2and4strokeengines,andmaybe
usedincombinationwithothermeasurementstoevaluateignitionsystem
performanceatdifferentenginespeeds.
5.2 Spark burn (ring) time
The spark burn time, also called “ring time”, is the measurement of the period from
themomentasparkisinitiateduptothepointwhenitisextinguished,andisthemost
indicativemeasurementofperformanceoftheignitionsystem.Abnormallylongorshort
burntimesmayindicatesomeproblemintheignitionmodule,sparkplug,fuelmixture,
cylindercompression,etc.
5.3 Spark plug voltage
Sparkplugvoltagevaluesareusefulforcomparingtheperformanceoftheignitionsystem
betweencylinders.Thismaybeusedtodiagnosecommonproblemslikemisres,broken
sparkplugwires,etc.Sparkplugpeakvoltagesmayvarywidely,arelessconsistentand
notalwaysindicativeofaproperlyworkingignitionsystem.Ontheotherhand,observation
ofthesparkplugvoltagewaveformortrendmayproveusefulindiagnosingignitionand
mechanicalproblems.
5.4 Dwell angle (for ignition systems using spark plug wires only)
Dwellangleisameasurementoftheangleofrotationofthecrankshaft,betweenthemoment
inwhichtheprimaryoftheignitioncoilisenergized(e.g.pointcontactsclosed)andthe
sparkisgenerated(e.g.pointcontactsopened).Itsmainuseisindeterminingifthereis
enoughangle(ortime)toenergizetheprimaryoftheignition,andnotsomuchastocause
theignitioncoiltooverheatandfail.Dwellanglesarespeciedforaparticularengineand
RPM,andusuallyadjustedinthemechanicaldistributor/pointassembly.
5.5 Current ramp time (for coil on plug and coil near plug only)
Ramp time is measured from when the primary coil current rst begins to increase to
whenitstopsincreasing.Thecurrentmaystopincreasingbecausethecoilhasreached
itssaturationpoint,oritisinterruptedtogenerateaspark.
Ramp timemeasurements are useful fordiagnosing problems in theprimary circuit of
theignitionmodule.Abnormallylongramptimesmayindicateexcessiveprimarycircuit
resistance,lowinputvoltage,thatthewrongmoduleisinstalled,etc.Shorterthannormal
ramptimesmayindicateashortedprimarycoil,thatthewrongmoduleisinstalled,etc.