FAULTLESS DIAGNOSTICS FROM THE MARKET LEADERS IN AUTOMOTIVE OSCILLOSCOPES
THE PICOSCOPE HAS BEEN CHOSEN BY MORE MANUFACTURES FOR THEIR DEALERS THAN ANY OTHER.
Move to the next level with the Pico oscilloscope and eliminate guesswork One-off payment with software upgrades and technical support for life
Suitable for use with any modern vehicle The Pico Automotive Diagnostics Kit can be used to measure and test virtually all of the electrical and electronic components and circuits in any modern vehicle including: Ignition (primary and secondary) Injectors and fuel pumps Starter and charging circuits Batteries, alternators and starter motors Lambda, Airflow, knock and MAP sensors Glow plugs / timer relays
www.picoauto.com/auto471 Click on the advert for more information EVERYDAY DIAGNOSTICS: INTERMITTENT MISFIRE
2002 Ford Explorer Intermittent Misfire Vehicle details: 4.0 SOHC V6
THE PROBLEM This is the tale of a 2002 Ford Explorer with an idle quality complaint. According to the customer the idle would surge, especially when first started and would even stutter a bit when put into gear. As the engine warms up, the problem fades and is much less noticeable. When I got the car, I could feel the misfire and an overall harshness in the way the engine was running. The history revealed that this complaint had been raised many times before and treated without success. The last tech assigned replaced a leaking vacuum line and cleared the memory, so there were no codes or Mode $06 information available for me to see. I had a new diagnostic aid I hadn’t had the chance to put to the test yet, the ACE Misfire Detective, a software program designed for use with the Pico Technolgy DSOs (Digital Storage Oscilloscopes) and the SenX FirstLook pressure sensor. By monitoring the exhaust pressure pulses on a running engine and synching them to the #1 cylinder’s ignition, the software can help identify not only the amount of misfires,
but which cylinders are contributing to the problem.
THE DIAGNOSIS I ran three tests using this software, and all three reported misfires on cylinders 1, 2 and 3 with #1 being far and away the worst offender (see figures 1a below and 1b online).
The counts, however, were not consistent and one test reported misfires on some of the right bank cylinders. I wasn’t looking for exactly the same results…the counts were sufficiently different to raise an eyebrow though. What would make the misfire rates differ that much? On with the
www.picoauto.com/FORD1 Click on the advert for more information
investigation… Misfires are caused by ANY condition that affects the quality of the combustion process. That means variances in compression, spark and fuel can all contribute their fair share. The next step I take is to gauge the health of the engine, so a relative compression test was next on the list. Pico Technology have a diagnostic software of their own, and it performs a relative compression test by simply hooking up to the battery. The scope then measures the normal AC ripple coming in from the alternator, on the theory that if engine rpm is affected by misfiring cylinders (the engine slows down, even if only for a millisecond or two), the AC ripple wave will act like the crankshaft sensor and also vary in frequency. The results are then posted in a bar graph format, with the healthiest cylinder labeled as #1 and the rest listed in the normal firing order of the engine being tested.
To read the rest of this article please click here to link to the Pico Technology website.
Written by Pete Meier, for Motor Age Magazine
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