Using Oscilloscopes on Vehicles

WisdomAugust

The Secondary Ignition Waveform-2


Secondary Scope Pattern

WisdomAugust

The Secondary Ignition Waveform-1

The voltage required to fire the plug is determined by the greatest gap in the circuit.

It is not a measure of all the gaps in the system. A better terminology would be

"dominating gap," because kilovolt (Kv) demand increases with spark gap under

compression. If a 0.045-inch gap outside the combustion chamber requires 2 Kv to

jump the gap, this same gap under compression may require 10 Kv for the plug to

ionize, providing fuel is present to help conductivity.

WisdomAugust

Q: Why a Scope If You Have a Scan Tool?

A: Very few shops have a scan tool for every vehicle, and using a scope for drivability problems is an alternative.

The scan tool might spot a misfire, but the scope does more than just find the location. It identifies under what

conditions (speed or load) the problem occurs and provides a chance to evaluate the cause. Because you can

compare each cylinder under the same load or driving condition, you can show the customer potential future

misfires and prevent comebacks.

WisdomAugust

Q: What can I expect from a technician using an oscilloscope?

A: From experience, oscilloscope users are dedicated professionals who have invested both time and money (often their own) to improve their diagnostic capability in the ever increasing complexity of today’s vehicles. You can expect your vehicle repaired in a realistic time backed with proof of component failure with supporting literature of before and after fix that will deliver confidence in any repair.?

WisdomAugust

Q: Why use an oscilloscope not just a scan tool?

A: Once connected to the components the technician is able to look at the cause and effect of various sensors on the idle control system. A wiggle test is such a simple yet effective technique when looking at signals that may be interrupted due to wiring failures, connection issues, and heat damage. Only the oscilloscope can respond fast enough to display these “glitches” where the scan tool would miss this vital “drop out” in signal integrity so leading the technician on a potential goose chase. The oscilloscope can also be used during road tests when most faults occur, allowing the technician the same high speed capture ability under the operating conditions reported by the customer. The oscilloscope can record the signals above and when the fault occurs the technician is able to pause and playback the captured data, zoom, measure, and evaluate the signals to conclude a diagnosis as to why the vehicle may have stalled