Engine cranks but won't start. Common problems

In this guide, we are going to look into no-start problems when the engine cranks, but won't start. If your engine won't crank at all, check the first part No-start: Car won't crank. If your car has a push button start system, read this guide.
If your engine cranks normally, but won't fire up, you know that at least your battery is good and the starter motor works. Let's look at the most common possible causes:

• Engine is flooded
• Bad fuel pump or fuel pump relay
• Failed airflow sensor
• Bad crank or cam sensor or circuit
• Problems with the engine computer (PCM) or PCM circuits
• Faulty ignition coil pack
• Wrong timing
• Low compression
• Common no-start problems

Engine is flooded

This problem is common, especially in high-mileage vehicles. A car stars then stalls out and doesn't re-start again. Mazda RX-8 was famous for flooded engine. What happens, the excess gasoline fouls spark plugs and washes of the oil from the piston rings (or rotor seals in RX-8) reducing the compression. Your mechanic may advise to replace or at least remove and dry out the spark plugs and re-charge the battery. Once spark plugs are removed, the excess gasoline dries out. With new spark plugs and re-charged battery, the engine usually starts well. For the RX-8 there is a special de-flooding procedure that you can find on one of the RX-8 forums. Check this tread, for example.

Bad fuel pump or fuel pump relay

This problem is also common in high-mileage cars. One day, a fuel pump just stops working and the car doesn't start. When you take your vehicle to the repair shop, your mechanic will need to run a few tests. Typically they test the fuel pressure among other things and check the fuel pump electric circuit and the relay. A bad fuel pump or main relay is actually common in some Honda, BMW and other vehicles. Replacing the relay is not expensive. If your fuel pump is failed, we recommend to trust this job to a qualified technician, as in many cars the fuel pump is installed inside the gas tank.

Bad mass airflow sensor

In many modern cars a failed mass air flow sensor can cause a car not to start. Often a car starts for a quick second, but stalls out immediately. Many mechanics use known good mass air flow sensor to test if the engine starts. Some mechanics will try to disconnect the mass air flow sensor altogether to see if the car starts without it. Replacing a mass air flow sensor is easy and not very expensive. Read more about a mass airflow sensor.

Bad crank or cam sensor or wiring

A crankshaft position sensor (crank sensor) is an important device measuring the engine RPM and tracing the crankshaft position. Without it a car won't start. Often a crank sensor or its wiring gets damaged. This may cause a car to stall out or not to start. Often this happens intermittently. A cam sensor works similarly except it measures the rotation of the camshaft. Many new cars have two camshaft sensors, one for each camshaft. Problems with cam and crank sensor are common in many vehicles, including older Nissan and Chrysler models. A crankshaft sensor can be tested with a scan tool or a multimeter. Read more about it here: Crankshaft position sensor.

Problems with the engine computer (PCM) or PCM circuits

A faulty engine computer or PCM is rare, but some cars had known issues with it, including older Nissan Sentra and Ford Escape models. We had seen problems where the PCM circuit or fuse were shorted after boosting a dead car battery. In some cars, you can tell that the PCM is not powered by watching the "Check Engine" icon when the ignition is turned on: when the PCM is not powered, the icon does not illuminate. In some older Mazda cars, the corroded wire at the PCM fuse in the fuse box is known to cause a no-start issue. The PCM is an expensive part, however it is usually covered by an emission warranty (8 years or 80,000 miles).

Faulty ignition coil pack

In some older cars, including GM and Volkswagen, a faulty ignition coil pack was known to fail. Often it would happen in a rainy weather or after washing the engine. Your mechanic can quickly test the coil pack. The part is not very expensive and can be purchased online. Most newer cars have separate ignition coils for each cylinder. Although they also very common to fail, they won't cause an engine not to start. Read more about ignition coils.

Incorrect timing

Often this problem happens after a timing belt or chain is replaced. If a car doesn't start after this repair, the timing must be checked first. In cars with a timing belt, an old belt can skip altering the timing. The repair might be quite expensive, as the incorrect timing can cause bent valves in the "interference" engines. In non-interference engines, replacing a timing belt and resetting the timing can fix the problem. Read more about a timing belt. In some cars with a timing chain, this problem may happen when the engine is very low on oil.

Low compression in the engine

In most cases an engine loses compression after overheating or when a timing belt or chain skips. The usual solution is to replace the engine. Replacing the engine with a used unit costs from $900 to $2500 depending on the part cost and the complexity of the work. With today's well-developed network of auto recyclers locating a used engine is not difficult. We have seen may engines replaced successfully.

Researching common problems can provide an answer

If your car won't start, there is a good chance that someone else had a similar problem with the same car as yours and already found a solution. There are websites where you can search problems reported by other owners:
Safercar.gov - click 'Vehicle Owners' then 'Search Complaints'.
Carcomplaints.com - search for common complaints.
For example, if you search the NHTSA complaints at Safercar.gov for the 2002 Chevrolet Impala, selecting "Electrical System" you will find a number of no-start complaints related to the "Passlock" feature. Now, Google "Passlock" and you will find a number of treads at various forums describing the problem and ways to fix it.
By the way, searching online forums dedicated to a make and model you have can also be helpful in finding a solution for your problem.
You also can search Technical Service Bulletins (TSBs) for your car, if a similar problem already happened to other same-model cars, there is a good chance that the car manufacturer issued a TSB describing this problem.

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