Waveform Library

DIS Secondary Raster

This is a typical 4-cyl conventional ignition system secondary raster (stacked) display. Use this display type to view the burn time, burn kV, and the coil oscillations

Power & Waste

This screen shows both the power ignition waveform and waste ignition waveform for a DIS ignition system. Note the difference in the firing voltage between the power ignition signal and the waste ignition signal.

The reason for the difference in firing voltages is: the power ignition waveform is firing on the compression stroke and the waste ignition waveform is firing on the exhaust stroke.

Since the waste ignition firing is on the exhaust stroke there is no compression and no air-fuel mixture to burn, this greatly reduces the demand for kV. High kV on the waste ignition firing indicates secondary resistance, look for a worn spark plug, plug wire or high ignition coil on the secondary side.

DIS Power Parade

This is a typical power ignition waveform on a GM DIS ignition system in a parade display. Notice that cylinders 4, 5, and 6 have higher firing kV than cylinders 1, 2, and 3, but the burn kV and burn time is approx. the same. The cylinders with the higher firing kV are negative firing cylinders, the cylinders with the lower firing kV are positive firing cylinders. This is normal on most GM DIS ignition systems.

DIS Power Raster

This screen shows the power ignition waveform in a raster display. Use the raster display to better view the burn time, burn kV and coil oscillation.

DIS Waste Parade

This screen shows the waste ignition waveform for a DIS ignition system in a parade display. Notice the high firing voltage on cylinder #2, this is caused by a bad (high resistance) spark plug wire.

Additionally, cylinders #4 and #5 have higher than normal firing lines caused by marginal spark plug wires.

Higher than normal firing voltage in the waste ignition is caused by high resistance in the secondary side of the ignition system; worn spark plugs and/or spark plug wires or high resistance in the ignition coil.

Quick Ignition Primary

This is a typical primary ignition waveform for a conventional ignition system displayed in quick ignition. This display is useful when viewing primary ignition for each individual cylinder. Setup: primary lead connected to the negative side of the coil, sync lead connected to the cylinder you wish to view, ground lead connected to the negative side of the battery.

Quick Ignition DIS P & W

This is a typical power and waste ignition waveform for a DIS ignition system displayed in quick ignition. This display allows you to view the power and waste firing for the same cylinder. This display is particularly useful when trying to determine if a cylinder misfire is ignition or fuel related.

If the power firing voltage is high and the waste firing voltage is normal this would indicate a lean fuel mixture.

If the power firing is normal or high and the waste firing is also high that would indicate high resistance in the secondary circuit, plugs, wires or coil pack.

Setup: kV probe and sync probe connected to the same spark plug wire, ground lead connected to the negative side of the battery.

Quick Ignition Secondary

This is a typical secondary ignition waveform for a conventional ignition system displayed in quick ignition. Notice the lack of coil oscillations, this is normal in quick ignition due to the kV probe connection point.

Setup: kV probe and sync probe connected to the same spark plug wire, ground lead connected to the negative side of the battery.

Quick ignition can also display a parade pattern by connecting the kV probe to coil wire and the sync probe to #1 cylinder, then expand the time base to see the desired parade pattern.

DIS Coil Amperage

This is a typical ignition coil amperage waveform for a DIS ignition system. Notice the clean horizontal rise in current during the coil charge time and the sharp drop in current at the end of the coil charge time.

If the rise in current is sharp and nearly vertical this indicates a shorted ignition coil. If there is hash or turbulence in the wavefrom suspect a bad ground or defective ignition module.

Vehicle hookup: connect the milliamp probe around the b+ wire feeding the ignition coil.

Ford Idle Air Control

This is a typically good ford idle air control (IAC) motor waveform. The Ford IAC waveform has its own unique "sawtooth" signature. The IAC valve is being pulsed and the duty cycle determines the volume of air through the valve.

A 100% duty cycle is fully open and a 0% duty cycle is fully closed. When checking this solenoid look for dropouts or spikes in the waveform that could indicate a problem.

Dual Oxygen Sensors Pre-Cat

These are typical OBD II PRECAT O₂ sensor waveforms at idle. Notice that the rich/lean humps are exactly opposite of each other, this is due to the exhaust pulses from each cylinder bank at idle being opposite of each other. This is normal. The waveforms will synchronize as the rpm rises above 2000 rpm.

Look for slow or unresponsive O₂ sensor waveforms indicating a lazy or malfunctioning O₂ sensor.

2 Channel Oxygen Sensors

These are typical OBD II PRECAT O₂ and POSTCAT O₂ sensor waveforms on an Asian import ultra low emission vehicle (ULEV). The top (YLO) channel is the PRECAT O₂ sensor. The bottom (BLU) channel is the POSTCAT O₂ sensor.

Look for slow or unresponsive O₂ sensor waveforms indicating a lazy or malfunctioning O₂ sensor.

Channel Oxygen Sensors

These are typical OBD II DUAL PRECAT O₂ and single POSTCAT O₂ sensor waveforms at idle on a cold startup. This can also be viewed as a bad POSTCAT O₂ sensor on a vehicle at operating temperature.

Look for slow or unresponsive O₂ sensor waveforms indicating a lazy or malfunctioning O₂ sensor.

Cam & Crank Signal

This is a typical Asian import cam and crank sensor using the lab scope. Notice the blue channel cam sensor waveform has a hump on every third square wave, this is for cylinder id.

The cylinder ID hump is atypical among Asian import cam sensors. These particular cam and crank sensor waveforms are from a 1993 Isuzu trooper 3.2i DOHC V-6.

Channel Lab Scope

This screen shows the distributor reference (dref) waveform on the top (YLO channel) in relationship to the coil amperage waveform (blu channel) and coil primary (red channel) using the 4 channel scope.

These waveforms were captured on a non-computer controlled timing vehicle. Notice the correlation between the three waveforms.

DREF; EST; KNOCK; ECS

These waveforms were captured using the 4 channel lab scope. The top channel (YLO) is DREF, the (BLU) channel is EST, the (RED) channel is the knock sensor, and the (GRN) channel is the ESC input to the PCM.

Notice the ESC response to the knock sensor signal after a knock (presumably pre-ignition) is detected. This is normal operation of the electronic spark control system.

Fuel Pump Amperage

This is a typical fuel pump amperage waveform.

Injector Amperage

This is not a typical injector amperage waveform, the current is approximately double what most injectors are. This injector amperage waveform was captured on an infinity q45 at idle.

Normal injector amperage peak is 3 to 8 amps on a MPI system and 3 to 4 amps on a TBI system. If the rise in current is sharp and nearly vertical this indicates a shorted fuel injector. If there is hash or turbulence in the waveform suspect a bad ground or defective injector driver.

Injector Amperage (P & H)

This is a typical peak and hold injector amperage waveform. Notice how the amperage reaches the peak quickly then is reduced to approximately ¹/₃ for the remainder of the waveform, this is normal.

On a peak and hold injector sometimes called current limited, the PCM supplies full current to open the injector, then reduces the current for the remainder of the time the injector is open. If the rise in current is sharp and nearly vertical this indicates a shorted fuel injector.

If there is hash or turbulence in the waveform suspect a bad ground or defective injector driver.

Injector Volts & Amps (P & H)

These are typical amperage (top) and voltage (bottom) waveforms for a peak and hold style fuel injector. Notice the correlation between the two waveforms. When the injector driver grounds the injector circuit the amperage starts to build. Once the injector is opened the injector driver reduces current to the injector, this can be seen as the drop in current in the amperage waveform and the first inductive spike on the voltage waveform.

When the injector driver releases the ground to the injector the current flow stops which causes the second inductive spike in the voltage waveform.

Setup: yellow channel; milliamp probe connected to the voltage feed wire for the fuel injector (remember to set the probe gain for the milliamp probe), blue channel; connected to the switched side of the fuel injector and the ground lead connected to the negative side the battery.

Bad DIS Power

This bad DIS power parade waveform was captured from a vehicle with a bad ignition module. The ignition module could not supply the coil pack for the #3 and #6 cylinders with enough current to fully charge the primary circuit, which resulted in low secondary voltage (kV) output. A weak coil pack or low resistance in the secondary circuit could also cause this waveform for the affected cylinders.

Bad DIS Waste

This bad DIS waste parade waveform was captured from a vehicle with (defective) spark plug wires on the #6 and #4 cylinders. During the waste ignition firing there is no compression and no air/fuel mixture to burn, which results in a very low demand for ignition kV (usually 3 to 5 kV). When viewing waste ignition, high firing voltage (kV) is caused by high resistance in the secondary circuit, worn spark plugs, plug gap too wide, worn plug wires, etc.

Because we are viewing the waste ignition firing, we know the problem is high resistance in the secondary circuit. By swapping the spark plug wires with that of other cylinders (the problem tracked with the wire swap) we were able to determine a spark plug wire problem.

Bad Ford MAP Sensor

This bad ford digital map sensor was captured using the digital MAF/MAP autometer. This vehicle was experiencing an extreme rough running condition as well as stalling out at times.

Notice the autometer shows the current frequency reading plus the minimum and maximum reading recorded, a histograph of the frequency, and a labscope display of the waveform.

Bad ECT with Oxygen

This screen was captured using the lab scope. The yellow channel is connected to the ECT sensor signal voltage (from ECM); the blue channel is connected to the O₂ sensor. This vehicle had no trouble codes and failed an emission test as a gross polluter.

Notice how the ECT signal voltage drops to 300mV and drives the O₂ sensor voltage high (900mV) full rich condition. The ECM would intermittently drop the ECT voltage to 300mV causing a full rich condition. The fix was to replace the faulty ECM.

Bad Diode Pattern 1

This waveform was captured using the diode pattern test located in the engine tests menu. This particular alternator has a bad rectifier, causing an AC voltage to ride on top of the DC voltage signal.

This AC voltage affected the pip and spout signals (Ford primary ignition signals) causing a no code driveability problem. The fix was to replace the alternator.

Bad Diode Pattern 2

This waveform was captured using the diode pattern test located in the engine tests menu. This alternator, like the previous alternator, has a bad rectifier.

This is another example of how a bad rectifier can affect the diode pattern. The fix was to replace the alternator.

Bad IAC Waveform

This waveform was captured using the lab scope. This is a good example of how an alternator with a bad diode can affect other signals that the ECM looks at. In this case it is an IAC motor.

When viewing waveforms that have a lot of hash always look at the alternator diode pattern as a possible cause.

Bad cct (Intermittent 5V Bypass)

These waveforms were captured using the lab scope. The top trace (YLO) is DREF. The middle trace (BLU) is EST. The bottom trace (RED) is the 5V bypass. Notice how the 5V bypass intermittently switches from 5V to 0V, causing the EST signal to switch from high (computer controlled timing) to low (base timing).

The 5V bypass signal is an output of the ECM to the ignition module controlling the switch from base timing (ignition module) to computer controlled timing (ECM). The ECM was intermittently losing the 5V bypass to the ignition module causing the vehicle to switch from computer controlled timing to base timing. The fix was to replace the ECM.

Bad cct (Defective DREF)

These waveforms were captured using the lab scope. The top trace (YLO) is DREF. The middle trace (BLU) is EST. The bottom trace (RED) is the 5V bypass. This vehicle had a defective DREF signal that affected the EST signal.

The cause of the defective DREF signal was a defective crank sensor signal to the ignitoin module. The fix was to replace the crank sensor.

Bad EST with Secondary

These waveforms were captured using the scope channel test located in the engine test menu. The top trace is the secondary ignition. The bottom trace (scope) is the EST signal. Notice the correlation between the two signals, the EST signal is not triggering the coil to fire for cylinders #3 and #4 in the firing order.

The scope channel is a good way to determine if an ignition problem is caused by the secondary ignition circuit or the result of a problem in the primary ignition circuit as with this problem. This vehicle had a good DREF signal to the ECM. The fix was to replace the ECM.

Bad ECM Power Relay

These waveforms were captured using the 4 channel lab scope and the trigger function. The top trace (YLO) is EST. The next trace (BLU) is primary ignition. The next trace (red) is crank reference. The bottom trace (GRN) is b+ supply voltage to the ECM. When the ECM b+ supply voltage dropped, the EST signal and primary ignition voltage was lost. The trigger function of the lab scope can be used to catch intermittent signal dropouts as in this case.