Why Your Car Might Be Running Rich or Lean — and What to Do About It

Jun 17
2 min read

“Too rich in the top end, too lean in the low end!”That’s exactly what we found with a VF V8 that had been back and forth to its original tuning shop with no real solution. Despite multiple attempts, the car still suffered from poor fuel efficiency, power loss, and unpredictable throttle response.

When the vehicle came to us, we diagnosed it properly and discovered fuel trims were off by over +30%—that’s massive! Once corrected, we saw an immediate improvement: better fuel efficiency and noticeable power gains across the rev range.

What Does It Mean to Be Running Rich or Lean?

Running Rich: Your engine is burning too much fuel compared to the air coming in. It smells like fuel, burns your wallet faster, and can foul spark plugs.
Running Lean: Not enough fuel for the air entering your engine. This can cause hesitation, loss of power, or even damage under high loads.

3 General Tuning Tips to Avoid These Issues

1. Always Start with a Diagnostic Don’t guess. Scan the vehicle and check the fuel trims, sensor data, and ECU logs. Modern cars will tell you what’s wrong—if you know how to read it.

2. Don’t Rely on “One-Size-Fits-All” Tunes What works for one VF V8 might not work for another. Every build, mod, and even climate can change the tune needs.

3. Work with a Tuner That Tracks Results Correcting +30% in fuel trims isn’t just a minor tweak—it’s fixing a core issue. Make sure your tuner understands how to properly dial in AFRs and trim corrections, not just chase dyno numbers.

The Bottom Line

Tuning isn’t just about making more noise or bigger dyno sheets—it’s about drivability, reliability, and longevity. If your car feels off, trust your gut. And more importantly, trust a team that knows how to make it right. 🔗 Get your custom Stage 1 tune: Revhigh Custom Dyno Tuning

📺 Watch more builds on YouTube: Revhigh Tuning Solutions

🛠️ Explore our performance packages: Performance Packages

📍 3/5 Bungaleen Court Dandenong South, VIC, Australia | 📞 03 9001 6375 | 🌐 revhigh.com.au

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