How to Fix an Engine Not Running

Is your engine not running you are in the right place. If the starter is not working please go here - Starter not working

What Goes Wrong?

An engine needs three things to run; Compression, fuel and spark. Because the engine depends on supporting systems to make these things happen such as the fuel and ignition systems a simple item such as a fuel pump relay will make the engine not run. When the engine is not cranking over a simple item such as a low battery can fix the problem.

How much does it cost?

Troubleshooting an engine that does not run and does not crank over will be different. If the engine is not cranking over and you have towed it to a repair shop to troubleshoot the problem it should cost between $30.00 if it's an easy and $140.00 if it a more complicated electrical issue. If the engine is not starting then more diagnostic time maybe needed. Again, there are simple and complicated problems for both of these scenarios.

Let's Get Started

This section is for an engine that cranks over but will not fire up.

1. Check the Security System

A security system is built into most vehicles which disable the ignition or fuel system when activated. Occasionally the system will simply become confused due to a glitch or a procedural error. If the security light is flashing when trying to start the car the system has been activated. Exit the vehicle and lock all of the doors with the windows up and then wait 20 minutes. Then unlock the vehicle by the driver's door lock or remote this should reset the alarm system and then try to start the engine. If the light is still flashing try the spare key. If the light then goes out it is because the frequency chip located inside the first key has gone bad. This could be due to age in which case you will need a new key from the dealership. If the light is not flashing continue with our guide.

2. Test Fuses

Fuses are used to protect various electrical circuits while supplying power to components such as the fuel pump, fuel injection and computer systems from suffering a short circuit and possibly causing an electrical fire. When these fuses blow the system they support stops working and the engine stops running. There are two methods of checking electrical fuses that protect various components. You can either pull each fuse out and inspect it by hand or use a test light to check its continuity. If a blown fuse is found check the system it belongs to by using the vehicles owner's manual or the identification chart on the fuse panel cover. Once the system is identified remove and inspect or replace the failed part and retry the engine. If the fuse still blows you will need to check the wiring harness for damage or a broken wire and repair it. If all fuses are good continue with our guide.

3. Check for Spark

The ignition system is designed to ignite the fuel air mixture inside the combustion chamber via the spark plugs. This is done by using an ignition coil, crankshaft and camshaft angle sensor along with the car's computer or PCM (Power Control Module). This system can stop working due to a failed ignition module or crankshaft angle sensor, or fouled or worn spark plugs which is very common. Testing the ignition system is an easy job that takes about five minutes and can be done using a test light or an extra spark plug. Connect a test light to ground and with one of the spark plug wires or coils disconnected. Crank the engine over while holding the tip of the test light about 1/4 inch (7mm) from the wire or coil terminal. Keep your hands clear of the test area to avoid accidental shock (non lethal). You can also insert a spark plug into the coil or wire and hold it against a metal ground. You should see a light blue spark in the gap this is telling you the system is working. If no spark is present suspect the crankshaft sensor will need replacing which is the most common problem.

4. Check for Fuel

The fuel system is used to deliver the proper amount of fuel at the correct time of the cylinder's compression cycle. This is performed by the fuel injection system which consists of a fuel injector for each cylinder. A fuel pump is located in the fuel tank with fuel lines that travel from the tank and up to the engine and into the fuel rail where the fuel injectors reside. Common fuel system problems are due to a fuel pump that has failed and is not supplying fuel pressure. Or the injectors are not operating correctly allowing the proper amount of fuel to be distributed into each cylinder for the piston to ignite. The easiest way to check if the fuel pump is turning on is to be very quiet and switch the ignition key to the on position without cranking the starter. You should be able to hear the pump running in the rear of the car. If you are unsure of its operation then you will need to test the fuel pressure. If no pressure is present then confirm the fuel pump being bad and needing replacement by using a wring diagram for your vehicle and probing the pump power wire using a test light.

5. Check Engine Trouble Codes

When a sensor or a controller fails in the engine computer system such as a crankshaft angle sensor, ignition amplifier or fuel pump controller it will stop the engine from starting. A check engine, service engine soon or MIL is telling you there is a diagnostic trouble code stored in the car's computer. These codes are designed to give you an idea of the system or sensor that is causing the problem. When these codes are present it means the computer has detected a failure which when corrected can fix the trouble. Today's cars are easier than ever to read the codes and it does not cost much for a code reader. If you do not have a code reader you can easily purchase one online from places like Amazon for about $40.00 (US). Plug the code reader tool or scanner into the ALDL port which is located on the driver's side near the bottom of the dash in most cases and gather any codes that are present. The video below shows a Honda Civic being done but it is the same for most cars.

6. Crankshaft Angle Sensor

A bad crankshaft angle sensor may not show up on a code scan as being faulty. When this sensor fails the computer see's the engine as not turning which may not be the fault of the sensor as far as the computer is concerned such as a bad starter. These sensors are located either at the front, middle or rear of the engine near the bottom of the block where the crankshaft resides. Replacement of the crank sensor takes about fortyfive minutes give or take depending on location and the accessories that maybe needed to be removed to perform the repair.

7. Check for Injector Pulse

Injector pulse is needed for the fuel to enter the engine through the injectors. This test will let you know if the computer is working by triggering the injectors for the engine to run. If there is no trigger then the computer is not powered up from the ECM relay or some other electrical issue is involved. Checking injector pulse can be done by using a test light while the engine is cranking. This will test if the injectors are getting a trigger signal from the computer.

8. Check Cylinder Compression

The engine requires compression to ignite the fuel to make the engine run. Cylinder compression is the result of the proper correlation of the crankshaft and camshaft while the pistons travel upward in the cylinder bore. When the volume of compression drops below about 85 PSI combustion is not possible. Cylinder pressure can be affected by a misalignment of the crankshaft and camshaft that can put the valve timing out of sync with the pistons. The most common cause for this is a jumped timing belt or timing chain. Checking engine compression is not too difficult and can be done with a spark plug socket and a compression gauge which you can rent for free from your local parts store. If compression readings are between 125 and 170 psi the compression is normal. Most of the time if one cylinder has the correct compression the engine will start and run. If one or more cylinders have low compression the engine will misfire and have a rough idle but still run. When the compression is low or non-existent the engine will crank over freely with little resistance to the starter a sure sign the chain or belt is the problem.

9. Plugged Exhaust System

Engine exhaust must be able to be relieved from the engine to allow it to run. If there is an obstruction such as a catalytic converter that has broken and plugged the exhaust system no exhaust gasses will be able to exit the engine. In this case remove the exhaust head pipe to allow make sure the exhaust system is not a problem.

Watch the Video!

What to look for when the engine will not run. This video shows how a mechanic would tackle this problem.

Obscure Starting Issues

There a few subsequent conditions which are more difficult to detect which will cause your engine not the start and run such as:

  • Water in the fuel tank
  • Electrical system wiring harness failure
  • Computer malfunction
  • Car was driven through a deep water puddle causing electrical components to get wet.

Before your car would not start did you notice anything out of the ordinary such as low power or a check engine light? This could aid in the troubleshooting and diagnosis process. If you are taking your car in for repairs mention anything you noticed before the trouble began to your mechanic.

Got Any Questions?

If you have any engine not starting questions or not cranking over questions, please visit our forum. If you need car repair advice, please ask our community of mechanics is happy to help you and it is always 100% free.

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