Car trouble is the worst. Cars are complicated, and dealing with problems often feels insurmountable.
But, it turns out that a lot of troubleshooting is simpler than it seems and can be reduced to just three steps. These three steps can’t fix absolutely anything, but if your car won’t start or if the engine isn’t running right, you can figure out most problems with the steps below.
Check the Spark
The first thing a combustion engine needs to run is spark. If you have a spark problem, it usually shows up in one of two ways. Either you’re going to a consistent shimmy while the engine is running (because one or more spark plugs aren’t firing correctly), or the engine won’t start at all.
In both cases, the problem is tied to electricity. So, there are a few tests you can run to really pin down the flow of electricity through your engine.
To do these tests, you’ll need a multimeter. You can get one from any hardware store or even Walmart, and they are not expensive.
The first thing you want to check is the battery. Simply check the voltage across the battery. It needs to read at least 12V, with 13 to 14 being a better sign of a healthy battery. If it’s less than 12V, the car won’t start (for most models).
If the battery is ok, the car should start. If it doesn’t, you very likely don’t have a spark problem and should skip to the next section. So, fire up the engine, and check the battery again while it’s running. Again, it should read at least 12V, and typically 14V is a sign that everything is healthy. This is showing you that there are no major electrical problems across the whole engine.
If the car starts but you’re getting shimmies, then you want to test the spark plugs. That’s a little more involved, so here’s a nice video tutorial to show you how to do it (it’s only a six-minute video).
Check the Air
The second thing your engine needs to run is air. That’s where the oxygen comes from for the combustion in your engine.
The thing about air is that it’s pretty easy to find, and there’s air in your engine right now. What that means is that airflow problems pretty much won’t prevent the engine from starting. Instead, airflow problems usually cause jerking, hesitant acceleration, and stalling.
Now, to test the airflow, you need something that can read flow rates and pressures. Fortunately, that tool is built into your vehicle already. It’s called the Mass Airflow (MAF) Sensor, and you’re actually going to test it with your multimeter too. If it’s working, then it will report any airflow problems to the vehicle’s computer, and you can read those with an OBDII scanner (or take it to any auto parts store to have it read for free).
How do you test the MAS Sensor? Here’s another short video.
Check the Fuel
Lastly, your vehicle needs fuel. If it won’t start, and the battery is fine, then the engine isn’t getting fuel (in the majority of cases). It could be that the tank is empty. It could be that the fuel filter is clogged. It’s possible that your fuel pump is dead. If you can find the culprit from those three, you know what to fix.
If the vehicle starts but stalls or has power or responsiveness problems (and the airflow is fine), then you could have a fuel flow issue. That’s also testable, but you’ll need a pressure gauge to do it. The good news is that you can borrow one from Autozone (they will require a deposit) and other auto parts stores.
When you have your gauge, you can follow this tutorial to test the fuel.
And, that’s it! Those are the three primary steps to diagnose an engine that won’t start or doesn’t run well.