Can a bad car battery cause engine misfire?
So everyone on hear that says a weak battery cannot cause a misfire is wrong especially with a Subaru!!! I recently ran into this exact same problem with my 2013 Subaru Impreza 2.0L. My car began to have a rough idle anytime I was sitting at a stop light. Then the CEL came on for a misfire in the cylinder and the dealership wanted me to do $1000 worth of work replacing the coil packs and spark plugs. I specifically asked them if a weak battery would cause the problem and they said no as well. I knew my battery was weak because I couldn't leave my car radio on for 5 min with out the battery dying. All battery tests I did said the battery was fine. Today I finally got sick of having to worry about it not starting from leaving the door open or the radio on while it wasn't running. Sure enough my check engine light turned off and now my car has greatly improved performance! Also my car now idles like it is supposed to. I'm thinking my fuel pump was not getting enough power which caused the misfiring. Either way the problem is fixed and I suggest looking into the battery first!
Why is my car shaking and the check engine light flashing?
A shaking vehicle AND flashing MIL ("check engine light") sound like the vehicle is misfiring on at least one cylinder. As @Anna Nguyen, @Brendan Sinclair, @Antoun Nabhan and others have said, it could be an ignition related problem. It could also be fuel-related. If one or more fuel injectors are clogged or dead, that would also cause a misfire in the affected cylinder(s). These are relatively cheap/easy things to check and fix.Other causes (which could be more complicated and more expensive) to fix include contaminated fuel, a bent intake or exhaust valve, a broken valve spring, a damaged piston/connecting rod, and on and on.I recommend getting a scan tool and checking the codes which are causing the MIL to light/flash and I also strongly recommend NOT driving the vehicle until the problem is fixed. If you continue to drive the vehicle as is, you will exacerbate the problem. Dumping unburned fuel into the exhaust due to a misfire will overheat and kill your catalytic converter. A more serious problem like a bent valve can eventually cause you to crater your engine (i.e.: completely destroy the engine).
If I took off the catalytic converter, will it make my fuel get better mileage?
Don't listen to the naysayers. A engine is a pump, anything you do to increase pump efficiency, is going to increase gas mileage. A new cat will not rais fuel consumption much, But if it has over 100,000 miles on it, You will see a marked increase or “restoration” of gas milage. This is especially true of cars with a secondary air pump. They are not exactly filtering the air, before its pumped into you exhaust.This is what gets fun. If you reprogram, or modify the O2 sensors signal to bring the engine to stylometric fuel ratio or just less, you will get a 5–10% increase in gas milage. This trick really shines in stop and go traffic. If you analyse the wave form of the upstream O2 sensors, you will notice it spends a lot more time rich, than lean. You are sitting at red lights feeding that Fat Cat, so it can make more smoke.All cars are set up to fuel that catalytic convert. This keeps them hot and working. Without extra fuel pumped thru the engine, that cat has nothing to do, cools down, and slowly plugs up. To bad your cat will plug up if you lean out the engine. Hint, Hint……….
I like to listen to fm radio without starting the car. Does it drain car battery?
Not perceptably, whilst the radio does use some power unless your car had a powerful amplifier the radio won't use much power at all. A bigger problem is that if you're switching the key to 'accessory' or 'ignition' to listen to the radio then you might be accidentally switching on other devices (eg fan, lights, seat heaters, etc) that do use significant power and will drain your battery.