So going up a hill at around 75 mph and on flat strips around 100 mph it feels like the car is suffocating for fuel and it bogs down like a sputter. If you keep on the gas it'll just keep with the sputter until you let off and check engine light will flash which I'm assuming is due to it detecting a misfire. I just changed the fuel filter and 91 is always used. Any idea what to check next?
Engine misfires can be caused by a list of problems, but there are a few suspects that occur more than others. The primary culprits are simple – spark or fuel – usually manifesting in spark plugs, plug wires, the coil(s) or the fuel-delivery system. 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. I would recommend having an expert from YourMechanic come to your location to diagnose your misfiring problem.
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