Episode 175

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Published on:

26th Feb 2025

Fuel Trims [E175]

Thanks to our Partner, NAPA Autotech

NAPA Autotech’s team of ASE Master Certified Instructors are conducting over 1,200 classes covering 28 automotive topics. To see a selection, go to napaautotech.com for more details.

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Introduction:

  • Fuel trims are a common topic in professional forums, classes, and diagnostics, often leading to bold diagnostic decisions.
  • Matt shares his experience of quickly diagnosing vehicle issues using fuel trims, even before leaving the parking lot.

Key Challenges in Discussing Fuel Trims:

  • The more you learn about fuel trims, the more nuanced and complex the topic becomes.
  • It’s difficult to generalize fuel trim behavior across all vehicles, as each system has unique characteristics.
  • Fuel trims are just one piece of data that must be factored into a broader diagnostic process.

What Are Fuel Trims?

  • Definition: Fuel trims are adjustments made to the base fuel schedule by the engine control unit (ECU).
  • Matt credits Matt Ragsdale on iATN for one of the best explanations he’s seen.

Two Primary Fuel Systems:

  1. Speed Density Systems:
  • Relies on the Manifold Absolute Pressure (MAP) sensor and engine RPM as primary inputs.
  • Engine control algorithms tend to be more complex.
  1. Mass Airflow (MAF) Systems:
  • Uses the Mass Airflow Sensor (MAF) and crank sensor (RPM) as primary inputs.
  • Simpler in design compared to speed density systems.
  • Modern systems often blend elements of both speed density and MAF systems.

Closing Thoughts:

  • Matt emphasizes the importance of understanding the nuances of fuel trims and how they vary across different vehicle systems.
  • He plans to dive deeper into the topic in future episodes, providing more detailed insights and practical examples.

The Aftermarket Radio Network: https://aftermarketradionetwork.com/

Remarkable Results Radio Podcast with Carm Capriotto: Advancing the Aftermarket by Facilitating Wisdom Through Story Telling and Open Discussion. https://remarkableresults.biz/

Diagnosing the Aftermarket A to Z with Matt Fanslow: From Diagnostics to Metallica and Mental Health, Matt Fanslow is Lifting the Hood on Life. https://mattfanslow.captivate.fm/

Business by the Numbers with Hunt Demarest: Understand the Numbers of Your Business with CPA Hunt Demarest. https://huntdemarest.captivate.fm/

The Auto Repair Marketing Podcast with Kim and Brian Walker: Marketing Experts Brian & Kim Walker Work with Shop Owners to Take it to the Next Level. https://autorepairmarketing.captivate.fm/

The Weekly Blitz with Chris Cotton: Weekly Inspiration with Business Coach Chris Cotton from AutoFix - Auto Shop Coaching. https://chriscotton.captivate.fm/

Speak Up! Effective Communication with Craig O'Neill: Develop Interpersonal and Professional Communication Skills when Speaking to Audiences of Any Size. https://craigoneill.captivate.fm/

The Aftermarket Radio Network

Remarkable Results Radio Podcast with Carm Capriotto: Advancing the Aftermarket by Facilitating Wisdom Through Story Telling and Open Discussion

Diagnosing the Aftermarket A to Z with Matt Fanslow: From Diagnostics to Metallica and Mental Health, Matt Fanslow is Lifting the Hood on Life.

The Auto Repair Marketing Podcast with Kim and Brian Walker: Marketing Experts Brian & Kim Walker Work with Shop Owners to Take it to the Next Level.

The Weekly Blitz with Chris Cotton: Weekly Inspiration with Business Coach Chris Cotton from AutoFix - Auto Shop Coaching.

Business by the Numbers with Hunt Demarest: Understand the Numbers of Your Business with CPA Hunt Demarest.

Speak Up! Effective Communication with Craig O'Neill: Develop Interpersonal and Professional Communication Skills when Speaking to Audiences of Any Size.

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About the Podcast

Automotive Field Theory
From Automotive Diagnostics to Metallica and Mental Health
Automotive Field Theory explores the forces that shape automotive repair, including the ones measured with a meter or oscilloscope and the ones that cannot be found on a wiring diagram.

Hosted by automotive diagnostic specialist, shop manager, and instructor Matt Fanslow, the podcast begins in the automotive aftermarket but rarely stays inside its traditional boundaries. Diagnostics, electricity, technology, leadership, psychology, economics, game theory, history, music, movies, family, and human behavior may appear unrelated. Look closely enough, however, and connections begin to emerge.

A vehicle may arrive with a technical fault, but the work surrounding it is rarely technical alone.

Information is incomplete.

People make decisions under pressure and uncertainty. Incentives shape behavior. Standards gradually drift. Good intentions produce unexpected results. The official process may say one thing while the system quietly rewards another.

Automotive Field Theory is an attempt to understand those interactions.

Drawing from real diagnostic work, shop management, industry conversations, personal experience, and an occasionally inconvenient level of curiosity, Matt examines not only how things work, but why they work that way, how they became what they are, and what apparently unrelated subjects might teach us about repairing vehicles, leading people, running businesses, and improving the automotive industry.

Some episodes begin with a failed component. Others begin with Metallica, quantum physics, professional wrestling, a historical disaster, a round of golf, or a question that refuses to leave Matt alone.

Eventually, they all enter the same field.