Q: Car is misfiring, was told it was the o2 sensor, it's not.

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I took my car in today to have them hook it up, the mechanic who came out and tested it said there were two issues, one was the o2 sensor and one code showed up as a misfire in the engine. I said what's causing the misfire he said it could be spark plug or coils etc. I said what about the o2, he goes well you could drive a long time without really having to replace that. I said okay so the misfire is probably what's causing the problem. He said yeah. Well the guy who's working in the office (not the same guy who tested my car) called me up and said they ran more test and said the o2 is causing the misfire. I was confused because that's not what the mechanic had told me earlier, but whatever. So I said okay If that's the issue then replace it. Well after they replaced it they called to tell me that the o2 sensor wasnt what was causing the misfire. So now they're keeping my car overnight. So now I'm wondering If I have to keep paying until they get it right.

My car has 100000 miles.
My car has an automatic transmission.

Engine misfires can be caused by many different problems and are generally caused by either a spark or fuel issue or in some cases, a combination of both. Spark related problems generally will result from things like ignition coils, crankshaft position sensor, spark plugs, spark plug wires or ignition modules not working properly. When the misfire results from a fuel related issue, this is commonly related to a lean fuel condition (lack of sufficient fuel supply to the motor). Fuel related misfires can be caused by many different things such as low fuel pressure, faulty or dirty fuel injectors, a faulty O2 sensor, a dirty or failing mass air-flow sensor, a faulty or dirty idle air control valve or a vacuum or intake leak. When the fuel supplied to the combustion chamber is insufficient, this results in an ignition (spark) that is igniting a less than balanced load of fuel and air. This results in a misfire or an explosion in the cylinder that is much less powerful than the other cylinders. This creates a loss of power that resonates throughout the motor additionally causing other problems with ignition and fuel timing. Due to the number of different things that may cause an engine misfire, the quickest and easiest way to diagnose this type of problem is to hook the vehicle up to a scanning tool which will download any potential fault codes that may have registered in the vehicle’s computer as a result of the poor running condition. I would recommend having an expert from YourMechanic come to your location to diagnose your misfiring problem.

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