What Causes Overly Rich Air-Fuel Mixture?
2 Answers
Reasons for overly rich air-fuel mixture: 1. Choke valve not opening or air filter element being dirty and clogged; 2. Improper adjustment of float chamber fuel level or poor sealing of the needle valve, resulting in excessively high fuel level; 3. Float rupture; 4. Clogged air bleed or malfunctioning economizer; 5. Excessive unscrewing of carburetor main jet adjustment needle or excessive wear of main jet. The air-fuel mixture in automobiles refers to the mixture of fuel (such as gasoline, diesel) and air. However, with advancements in automotive technology and fuel diversity, it now also includes mixtures with various combustible gases like natural gas, methane, coal gas, as well as ethanol, methanol, etc.
A rich fuel mixture simply means there's too much fuel and too little air in the engine. I've seen this a lot during repairs. The main causes are: a dirty air filter blocking the intake, forcing the system to compensate by injecting more fuel; faulty fuel injectors that might be stuck open, not sealing properly, or leaking; common sensor issues where the oxygen sensor or intake pressure sensor sends wrong signals to the ECU, causing it to command excessive fuel injection; ECU programming glitches, especially during cold starts where it overfuels; and a failed fuel pressure regulator causing excessively high fuel pressure that dumps extra fuel directly. These lead to skyrocketing fuel consumption, black smoke from the exhaust, and power loss - making driving quite dangerous. My advice: start by checking the air filter and replace if dirty. If that doesn't fix it, test fuel pressure or use an OBD scanner to pull trouble codes. Get it professionally repaired early to avoid burning more cash.
