Spark Running Rich? Common Causes & Quick Fixes

I had a similar issue with my 2020 Chevy Malibu. Got decent experience working with fuel system issues over the years. The symptoms you're describing match what I dealt with, rich mixture, check engine light, and that annoying jerky acceleration. My issue turned out to be a faulty fuel injector that was dumping too much fuel into the cylinder. After diagnosis, they found one injection valve was stuck partially open, causing the rich condition and killing my fuel economy. The repair involved replacing the defective injector, which ran me about 515 for parts and labor. After the fix, the engine smoothed right out and my fuel economy went back to normal. Before jumping to conclusions though, could you share: Any specific error codes from the check engine light? Does it run worse when the engine's cold or warm? Notice any dark smoke from the exhaust? How many miles on your Spark? This info would help narrow down if you're facing a similar injector issue or something else like spark plugs or catalytic converter problems.

Thanks for the input. Already took it for a diagnostic scan and got P0172 code, system too rich. The engine definitely runs worse when cold and there's black smoke from the exhaust, especially during warm-up. Just had my last service at 32650 KM. The oxygen sensor readings are all over the place according to the scan data. Mechanic mentioned the air-fuel ratio is way off but wasn't sure if it's the fuel injector or something with the air filter system. The spark plugs look pretty sooty too when they checked them. Could you share what diagnostic steps your shop took to confirm it was specifically the injector? Want to avoid replacing parts unnecessarily.

Yeah, those symptoms match my Malibu's issues exactly, especially the black smoke and P0172 code. The sooty spark plugs are another big clue, had the same thing when my injector was acting up. My mechanic did a pretty thorough diagnostic process: First ran injector pulse tests to check spray patterns, Monitored live fuel trim data while running, Used smoke testing to rule out vacuum leaks, Checked intake manifold for any cracks or leaks, Tested fuel pressure at the rail The testing showed one injector was flowing about 30% more fuel than the others. They could actually see the uneven spray pattern when they pulled it. The intake manifold and vacuum system were fine, and fuel pressure was within spec. Since your symptoms are identical, including the oxygen sensor readings jumping around, I'd bet you're dealing with a bad fuel injector too. The rich condition and black smoke are classic signs. Those clogged spark plugs are just collateral damage from all the excess fuel. Worth getting those specific injector tests done before replacing anything. Once they pinpoint which injector is the culprit, it's a straightforward fix. The improved fuel economy alone after the repair will help offset the cost.

Thanks for breaking down the diagnostic steps. That's really helpful info about the injector testing process. I'll definitely ask my mechanic to run those same checks, especially the pulse tests and fuel trim monitoring. My symptoms do seem to match your injector problem exactly, the black smoke, rough cold starts, and wonky oxygen sensor readings. The P0172 code and sooty plugs make even more sense now knowing how your situation played out. I'll get it back to the shop and have them focus on testing the fuel injectors first before looking at other components. Rather spend the money on proper diagnosis than waste cash throwing parts at it. Will update once I know more about what they find with the spray patterns and fuel trims. Good to know the repair cost was reasonable in your case too. The fuel I'm wasting right now with the rich condition is probably costing me more than fixing the bad injector would.