Master driveability diagnostician and Motor Age magazine’s Technical Editor Brandon Steckler is back with a follow-up video to The Trainer #148- A Well-Fed CAT is a Happy CAT. However, this time Brandon first walks us through the operation of the classic Zirconium dioxide oxygen sensor that has been used for decades in the computerized fuel injection systems across the automotive industry.
Afterward, Brandon compares that to the operation of the newer Wide-range air/fuel ratio sensors (WRAFs) that can be found in almost all internal combustion engine vehicles today. As the advancement of technology carries on, the ability to maintain fuel control has improved drastically. The older Zirconia sensors could very accurately indicate a rich or lean condition but that was about it.
With the technological advancements found in the WRAFs, not only can the systems indicate “rich or lean,” but now can show just how rich or how lean the exhaust gas content is. Air/fuel ratio excursions between Lambda 0.78 (22% rich of stoichiometry) to as high as Lambda 1.64 (64% Lean of stoichiometry)! This led to a drastic improvement in fuel injection control to maintain stoichiometry (or whatever air/fuel ratio the PCM desires), even under various transient conditions.
With today’s technology, “rear fuel trim” has been implemented. This minor corrective factor works hand-in-hand with both short-term and long-term fuel trim to accomplish total fuel trim. Rear fuel trim is responsible for not only optimizing the performance of the catalytic converter, but to maximize and extend its lifespan and even correct for a degrading catalyst.
With older technology, the goal was to maintain near-stoichiometry to ensure the catalyst can function. This limited how far away from stoichiometry the air/fuel ratio could travel. With today’s technology (like WRAFs and rear fuel trim), manufacturers can tweak the air/fuel ratio as they please (for example: to reduce NOx or improve MPGs) so long as the catalytic converter is still functioning efficiently.
Tune in to this episode of Mastering Diagnostics to witness how the WRAFs, rear HO2 sensors, and software strategies (for rear fuel trim) are easily displayed with the Bosch ADS 625X professional scan tool. Read more about the ADS625X here.
