Diagnostics and Drivability

Figure 5- Displayed are scope patterns that illustrate how volts leads the amps in an AC powered circuit that’s mostly inductive (L) and the opposite when the AC powered circuit is mostly capacitive (C). “ELI the ICE man” is a simple mnemonic to help remember the differences in “phasing” between volts and amps in the two different types of AC circuits.
With AC current, what you don’t know can hurt you, damage your test equipment, and fool your diagnostics.
March 1, 2022
Photo by author
Figure 2- Unfortunately, many technicians don’t realize the impact shotty circuity repairs can have on a diagnosis. Technician-induced faults can be some of the most difficult to find. In this case, at least six additional faults were created due to improper repair.
Oct. 11, 2025
Photo courtesy of Keith Perkins
Figure 1 — Perkins' shop uses the Autel Ultra S2 for its artificial intelligence-driven picture system.
Oct. 8, 2025
Photo courtesy of Scott Brown
Figure 4 — Modern vehicle network wiring
Oct. 7, 2025
fig_8__calibration_targeting_equipment
Sept. 4, 2025
Photo by author
The duration of the intake valve was significantly insufficient at only 51 degrees. This suggest either a significantly worn cam lobe or lifter issue. Considering all cylinders suffered the same issue, the likely fault was air-bound/collapsed lifters. The engine was cranked repeatedly to purge air from the lifters and the engine started/ran normally.
Aug. 13, 2025
Photo: Motor Age Training and TST Seminars
Spacing out rear O2 sensors with spark plug non-foulers have been used with varying effectiveness for years to try and desensitize the downstream sensors by moving them out of the direct exhaust flow. This practice is not only highly illegal but has been made mostly ineffective by some of the more advanced OSC testing procedures in newer vehicle models.
Aug. 12, 2025
Photo by author
Fig. 1: It’s engine bay configurations like this Aston Martin V12 that make the tried-and-true tests like the compression test (with a mechanical gauge) a tough pill to swallow. These tests, intended to be easy, could take hours to perform.
Aug. 11, 2025
Photo by author
The relative compression trace and cranking intake-pressure traces offer clues about overall breathability of the entire engine from one quick-to-grab capture.
Aug. 7, 2025

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