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Q: Cranks but won't start

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2002 Buick Century Custom 3.1L Car seems to crank a bit slower than normal, won't start. Replaced battery and starter. Cleaned battery side post terminal connectors. Removed and cleaned Ground connections to chassis, eng fuse box and transmission area as well as positive connection to new starter. During attempted start there is an air puff sound from engine bay followed by a small bit of smoke (also in engine bay) that smells like unburnt fuel/exhaust. Seems to originate from either intake manifold area or throttle body. I know the exhaust manifold gaskets need replaced and car was running rough (like O2 sensor or IAC) but I cannot get it to start at all right now. I've provided as much info as I can think of hoping someone can give me some direction as to what to check next. (I have not checked spark plugs yet).

My car has 87000 miles.
My car has an automatic transmission.

You are right on track. You may be dealing with several issues at once. The first thing you should do for this starting issue is check for proper spark. You need to check with an actual tester, and do a visual inspection of the plugs and wires themselves. You should also look to do a quick fuel pump check. Turn the key on and listen for the pump to prime. You may be able to hear this from the driver seat, but you may need to listen closer to the tank. This is a good sign that the pump is working correctly.

When was the last time you changed the fuel filter? This becomes clogged and cuts off your fuel supply. Next, after that will be the exhaust. The engine must exhale if it is going to inhale and start the combustion cycle. The O2 sensor could be at fault. But you will want to check the catalytic converter as well. A simple knock on it (when its cool) will tell you if the filter inside has become brittle and broken inside of the unit. It should not rattle or should like anything is moving inside. These can become lodged in the pipes and cause an engine malfunction. But that is rare with newer vehicles. If you would like to have a proper diagnosis for this, a certified professional from YourMechanic can come to your car’s location to inspect the starting problem and address this issue correctly.

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