How to Fix an Engine Not Running

There is a difference between an engine that does not run and one that does not crank over. If an engine does not crank over (electrical starter) it has to do with the starter motor not working and is completely different than an engine that does not run and produce power. If your engine turns over (cranking) but does not run you are in the right place.

What goes wrong?

A combustion engine demands three things to run, compression from the pistons and valves, fuel from the pump and injectors and spark from the ignition system and spark plugs. If one of these processes is not working the engine will not run.

How much does it cost?

Non-running issues will be different for each application. Some cars have popular items that go out which the dealer usually has in stock (they already know what goes wrong with their cars, but won't tell you). If you are stuck between a bad crankshaft angle sensor (about $67.00 US) or a PGM FI relay (about $56.00 US) call the dealer to see which one they have in stock, more times than not this will be the problem. If the engine has lost compression due to a timing belt failure labor cost to remove the timing cover and replace the belt should be about $700.00 to $900.00 (US) on average. The timing belt and tensioner replacement kit cost about $140.00 US so you can save money by doing the work yourself.

Get it going!

Sometimes you can get the car going with a large object or hammer for example: when the key is in the "on" position without cranking the engine and you don't hear the fuel pump running the motor can be in a "dead spot". This is a common problem and when it occurs take a large object and rap the bottom of the fuel tank. This creates vibrations in the fuel moving the motor armature slightly which can help the pump run and the engine to start. If this works the pump is still bad and needs to be replaced because it will happen again, but it can get you going.

Popular engine not running causes

  • Bad fuel pump
  • Shorted crankshaft angle sensor
  • Security light flashing
  • PCM power relay not working
  • Broken timing belt
  • Jumped timing chain
  • Melted fuel pump relay terminals
  • Popped engine fuse
  • Worn out ignition switch

Let's get started

Observing lights and sounds when the engine is not running is essential. This practice can give you a direction without diagnostic equipment. 

The easy stuff

  1. When cranking the engine over does the security light flash? Each manufacturer disables the engine in different ways when in security mode. Occasionally the system will become confused due to a glitch or a procedural error meaning the alarm system must be reset.

  2. It needs to be quiet for this next test. Turn the ignition key "on" without cranking the engine over. You should hear the electric pump in the gas tank run for about five seconds (a low hum). If you hear nothing something has failed in the pump electrical system such as the control relay, fuse, computer or fuel pump (most popular).

  3. Next, crank the engine over and listen to how it sounds, does it sound faster than usual? (like its laughing) This can mean the timing belt or chain has let go and the engine has no compression allowing the starter motor to turn the engine more easily. Perform a compression test to confirm the failure. Observing the engine camshaft not rotating through the oil filler cap when cranked over will also confirm the problem.

  4. If you can hear the starter motor loudly engage (thud) and then nothing it can mean the engine has locked up due to a mechanical failure. To test for this use a large breaker bar into the harmonic balancer bolt and try to turn the engine by hand which will have some resistance but still turn.

  5. Out of gas. I know what you are thinking and I wish I could say a car has never been towed to a shop simply because it didn't have fuel in the tank. In the driver's defense if the gas gauge sticks at 1/8 or the fuel level sensor goes bad so there is no way to know the fuel level unless you track the mileage of each tank.

Minor testing

  1. Checking the fuses is easy to do and can be done in just a few minutes using a test light or visual inspection. Fuses fatigue causing them to blow which will cut electrical current to crucial components such as the engine computer. This fuse will be under the hood in the fuse panel which should be clearly marked. Simply remove the panel lid and begin the inspection.

  2. Spraying starter fluid into the throttle body while cranking will help determine if the problem is fuel or ignition related. If the engine is cranking over and not running while the fluid is being sprayed (gas pedal depressed slightly) it's telling you the problem is spark (ignition system) related. If the engine runs for a short time you know the problem is fuel (fuel system) related.

  3. When the ignition switch is turned on you should hear the main system relay pull its contacts together which supplies power to the computer systems. This relay is named different things from each manufacture such as PGM-FI or Engine Control Relay and will be located under the hood inside the fuse and relay panel (fuse box). Remove the lid to locate the relay. While touching the relay have a helper turn the key on, you should be able to feel the relay work (small click). If not, test the relay or swap it out for a different relay in the panel to see if that works.

  4. Pull a spark plug! This easy easily done and by observing the condition of the plug it can give a clue to the problem. If the spark plugs are dry suspect fuel issues, if wet with fuel suspect an ignition problem and if the plug is flat black the electrode is shorted not allowing the spark to jump the gap (replace the spark plug with new).

  5. Scan for codes, we mention this last because 9 times out of 10 the computer will not tell you why the engine is not running. Engine computers are set up to provide trouble codes only when the engine is running, but you might get an error telling you the engine computer is bad so it's worth a try.

Little Deeper

  1. No Spark: If the engine will not run on starting fluid we need to confirm a "no spark" condition. Remove the ignition coil or spark plug wire and set it next to a good ground (about a 1/4 inch - 7mm) or insert a test light into the boot to check for spark. When the engine is cranked over you should see a light blue spark in the gap telling you the system is working. If no spark is observed the most popular reason is a failed crankshaft angle sensor. This sensor is located near the crankshaft at the rear (bell housing), middle (block) or front of the engine and is pretty easy to change in most cases. When the crank sensor goes bad it usually will not set a trouble code.

  2. No Fuel: If the engine runs on starting fluid there is a fuel delivery issue. The car's fuel pump resides at the top of the list for this system failure. Located in the gas tank the fuel pump is an electrical motor connected to a fluid pump which goes out in time. Some cars have an access hatch in the trunk or under the rear seat to help service the pump while others the gas tank will need to be removed.

  3. No Compression: If the engine has spark and will not run on starting fluid the problem will be compression related (or rarely have a completely clogged air filter or catalytic converter) This means either the timing belt or timing chain has let go not keeping the piston to valve correlation correct or nonexistent so the engine cannot create compression.

Watch the Video!

Engine will not run? This video shows how your mechanic would tackle this problem.

Obscure Engine Non Running Issues

There a few subsequent conditions which are more difficult to detect:

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


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