🔧 Case Study: Tracking Down a Rich Running Issue on a Honda K24A Engine

Allan Burlace
May 5
2 min read

At Agnews Auto Services, we specialize in getting to the bottom of tough diagnostic problems. One recent case involved a Honda running rich — using too much fuel, fouling plugs, and idling rough. It had already been to a couple of workshops without success. Here's how we cracked it.

🔍 The Symptoms:

Poor fuel economy
Hesitant throttle response
Strong fuel smell from the exhaust
No check engine light
LPG system fitted and previously tuned

🧠 The Investigation:

We started by pulling live data using our scan tools. The fuel trims were way off — indicating the ECU was trying hard to lean the mixture out. But why?

We checked:

Oxygen sensor readings — working, but reporting rich
MAF sensor data — normal
Injector pulse width — longer than expected
Fuel pressure — within spec
LPG vs petrol switching — confirmed active

Next up: smoke test. We found no major vacuum leaks. Compression and timing were both solid. That’s when we shifted focus to the LPG system.

🛠 The Fix:

After isolating the LPG system, we found a small leak at the mixer, allowing gas to flow in even when the car was on petrol. This tricked the ECU into thinking the car was running lean, so it dumped in more fuel to compensate — leading to the rich condition.

We also discovered the valves were tight, especially on the intake side. These engines are known for tight valve lash over time, which affects airflow and combustion.

With the LPG leak fixed, and a valve clearance adjustment done, the trims came back into range. The idle smoothed out, throttle response improved, and fuel economy returned.

💡 Lessons:

Always start with data, but don't ignore mechanical basics
Aftermarket systems (like LPG) can introduce tricky variables
Tight valves = common issue on K-series Hondas

✅ Result:

Another happy customer and another challenging case solved. If your vehicle’s acting up and no one can figure it out, bring it to Agnews — we don’t guess, we diagnose.