Your vehicle’s engine may refuse to operate as expected for several reasons. The culprit is always related to the three things your engine needs most: fuel for combustion, sufficient compression within the cylinders, and a spark. Without all three, the engine will not perform as it was designed. The problem is, each can be affected by other parts and systems, making it difficult to diagnose the root cause of a problem.
In this article, we’ll focus primarily on the factors that can cause your engine to crank (i.e. turn over), but not start. We’ll begin with the items that are easiest to troubleshoot, and advance to the more difficult items toward the end.
Inspect The Fuses First
This step sounds intuitive, but a lot of people neglect to do it. Whenever you’re experiencing issues with components that rely on your vehicle’s electronics, check the fuses before anything else. The reason cars have fuses is to protect the electrical circuits from an overload. If a particular fuse burns out, the part or assembly controlled by it will stop working. This includes your engine and parts that influence its operation.
Look in your owner’s manual to find out which fuses affect your engine. Then, open the main panel, remove the fuses, and inspect them. If the links inside are broken, the fuses are bad. If the links are intact, they are fine.
Pull The Trouble Codes
When your engine experiences any deviation from its normal performance, it will produce an OBD-II trouble code. This code is logged into your car’s computer. This allows a mechanic to retrieve it and have a better idea regarding where to start looking for the root cause of the deviation. If you have an OBD-II scanner, you can pull it yourself. You can purchase a scanner at many auto supply shops for less than $40.
Pulling codes from the computer is easy. A diagnostic connector is usually located in your vehicle’s cabin underneath the dashboard. You can plug the scanner into this connector in order to pull the codes from the computer. These OBD-II codes are alphanumeric (e.g. P1086, P1822, etc.). Once you have pulled them, look for their definitions online. This may provide helpful clues regarding why your engine refuses to start.
Examine And Test The Spark Plugs
Recall that one of the three things your engine needs is a spark. Hence, each cylinder has a spark plug (sometimes, two) that ignites the compressed air-fuel mixture within each cylinder’s combustion chamber. This results in a mini-explosion within the chamber. The explosion produces vapors that expand rapidly and push the piston downward, which turns the crankshaft.
Unfortunately, spark plugs become fouled over time. Deposits can accumulate on them and make it difficult to generate a sufficient spark. This can cause your engine to crank, but refuse to start properly. If the spark plugs appear fine, it’s time to test the pressure within the assembly.
Check The Combustion Chamber’s Compression
In order for the air-fuel mixture to ignite within the cylinder, it must be sufficiently compressed. This means the cylinder should be free of severe compression leaks. Often, the exhaust valve will fail to close properly, and thus allow air to escape during the combustion process. If a leak is severe, it can prevent your motor from starting.
You can purchase a compression gauge for less than $40. If the compression within the cylinders is fine, you’ll need to test your ignition system.
Is Your Ignition System Operating Properly?
There are several components that comprise your ignition system, and a failure that affects any of them can impair your engine’s performance. These include the spark plugs, distributor and distributor cap, rotor, ignition coil, and other pieces. Unless you’re experienced with automotive diagnostics, it’s a good idea to have a mechanic test these parts.
If your engine cranks, but will not start, follow the troubleshooting guide above. If you are able to isolate the problem to the fuses or spark plugs, you’ll be able to easily resolve it on your own.
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