My Engine Cranks But Won't Start
When your engine cranks but won't start or run, it could mean your engine is having trouble producing a spark, getting fuel, or creating compression. The most common causes are in the ignition (for example, a bad ignition coil) or fuel system (for example, a clogged fuel filter). However, the source may also be a mechanical fault (for example, a leaking valve), or faulty components in other systems.
What "crank-no-start" doesn't generally mean is a problem with the starter. If the engine cranks normally, you don't have a starting problem. If it isn't cranking right (the engine rotates slowly or doesn't rotate, or you hear weird noises or nothing when you try to start the engine), check this other practical guide to troubleshooting the starting system.
Whatever you do, avoid cranking the engine repeatedly with the hope that the engine will fire up. You may drain your battery of power and damage the starter motor in the process. Instead, try to use the charge left in your battery to locate the fault.
This guide will first give you six quick things you can check, and then three systems to troubleshoot—the spark, the fuel, the compression—using some simple and quick diagnostics. Then, for more help, you'll see a list of components in related systems that can be associated with a no-start condition.
Six Quick Checks
Check These Six Possibilities First
When trying to find out why your car doesn't want to start, keep in mind these possibilities.
- Fuel. For example, make sure there's actually fuel in the tank.
- The computer in modern vehicles monitors and controls a good number of sensors and actuators. Scan your computer memory for trouble codes before you do anything else. Even if the check engine light hasn't come on, you may find a pending code that can guide you in your diagnosis. False input or lack of input from sensors like the crankshaft position sensor (CKP) or camshaft position sensor (CPS) can prevent the engine from starting. Also, a bad throttle position sensor (TPS) may cut off the spark to the cylinders.
- Battery. If the engine cranks slowly, you may be dealing with a discharged battery, loose or corroded battery terminals or starting system wires
- Starting System. If the engine doesn't crank, or makes an unusual noise when cranking, you may have a starting system problem.
- The car's security system may have made an error that disabled the fuel or ignition system, or the chip in the key may have failed. To troubleshoot a built-in security system, consult your car owner's manual or consult with the shop that installed your alarm system.
- Check for a blown fuse that may be preventing a circuit from working properly, like the fuel injection or computer system.
Troubleshooting: Spark, Fuel, Compression
To operate efficiently, an internal combustion gasoline engine needs a good spark, the right amount of fuel, and good compression (a healthy mechanical condition). The lack of any of these three things will prevent your engine from starting.
So, the next three sections will list series of steps to help you find out whether your engine is lacking adequate spark, is not getting enough fuel, or has too low compression.
I. Do You Have Spark?
First you want to check that a good spark is reaching the cylinders. You can do this test without a spark tester, but it's better to use one, because a weak spark as well as a missing spark can prevent your engine from starting. If possible, use an adjustable tester so that you can test for 40KV, 30KV and 10KV spark.
- Select an easy-to-reach spark plug and unplug the spark plug wire, or coil wire, or coil on plug (COP).
- Set the spark tester to 40KV, and plug it in at the end of the spark plug wire or coil wire. Hook the spark tester to engine ground. To ground the tester, use an unpainted bracket or bolt on the engine. NOTE: If you are not using a spark tester, grab the wire with a pair of insulated pliers and place the tip of the wire about half an inch form ground (engine block, bracket, cylinder head). You still need a helper to crank the engine for you. The rest of the test is the same. You'll be able to test for the presence of spark but not its strength.
- While watching the spark tester, have an assistant crank the engine.
- You should see a bright spark jumping the gap in the spark tester.
If you don't see a spark, repeat the test. This time, adjust the spark tester to 30KV. If still you don't see a spark, repeat the test and set the tester to 10KV. If this time you see a spark or no spark, you have a problem in the ignition system. Consult your vehicle repair manual for your particular model for further diagnosis. Depending on your particular model, you may have a problem with an ignition coil, distributor, ignition module, igniter, or some other related component.
Other Checks You Should Do:
- On systems with a distributor: Check that the distributor cap isn't loose; inspect the distributor cap for moisture, cracks, carbon traces or some other damage; there could be faulty distributor components.
- If you haven't replaced the spark plug wires in more than three years, your wires may be worn.
- Also, check your car owner's manual or vehicle repair manual for the interval schedule for the spark plugs. Your may need to service (gap check and adjustment) or replace the plugs.
- If you installed new spark plugs and your car refused to start right after, double check that you installed the correct plugs for your vehicle model, and the plugs have the correct gap. Use a wire feeler gauge to check and adjust the gap.
II. Is Fuel Reaching the Cylinders?
After checking for spark, you need to check that the engine is getting fuel.
To Check a Carburetor or Throttle Body Injection (TBI) System:
- Take the lid off the air filter box and open the throttle plate (carburetor). On TBI systems, watch the fuel injector.
- Ask an assistant to crank the engine and see if fuel is being fed into the unit.
- If you don't see fuel being injected, your problem is in the fuel system. Make sure of the following:
- you have enough fuel in the tank,
- the fuel pump is working,
- the fuel filter is not clogged (consult your car owner's manual or repair manual for the service schedule),
- the fuel pressure regulator is working properly
- the fuel injectors are not clogged.
To Check a Multiport Fuel Injection System:
- First make sure the fuel pump is working. Momentarily remove the fuel filler cap.
- Ask an assistant to turn the ignition key to the On position, but don't start the engine.
- As your assistant turns the key, listen closely through the filler neck of the fuel tank. You should hear the whirring sound of the fuel pump motor being energized for two or three seconds. If you hear the sound, at least you know the pump is getting power; continue with the next step. Otherwise, you may be dealing with a faulty fuel pump or relay, a blown fuse, an electrical open or another problem in the fuel pump circuit.
- Detach the air cleaner assembly from the throttle body.
- Open the throttle plate and spray some starting fluid into the throttle body.
- Crank the engine.
- If the engine still doesn't seem like it wants to start, probably fuel is getting into the cylinders and your problems lies somewhere else. However, if the engine runs momentarily and dies, then the problem is that fuel is not getting to the cylinders. Check for a clogged fuel filter, or a bad fuel pressure regulator. Consult your vehicle repair manual, if necessary.
- If the incoming fuel line that goes to the fuel injectors has a test port (Schrader valve - a valve similar to the one on your tires), use a small screwdriver to press on the valve. Be ready with a shop rag to catch the fuel.
- Turn the ignition key to the On position for two or three seconds and then turn it off. Repeat the step two more times to prime the line with fuel.
- Then, press the valve with the screwdriver while catching the fuel with the shop rag. Fuel should squirt out through the valve. Instead, if a dribble of fuel comes out or no fuel, then check for a clogged fuel filter, a bad fuel pump or leaking fuel pressure regulator.
- If fuel squirts through the valve, plug a fuel pressure gauge to the test fitting valve and turn the ignition key to the On position and read the gauge. Then have an assistant crank the engine and read the gauge.
- Compare your gauge readings to the pressure specification listed in your vehicle repair manual.
- If pressure is lower than specification, your problem lies in the fuel system, possibly a faulty fuel pump, clogging fuel filter or bad fuel pressure regulator. Detach the vacuum hose from the top of the fuel pressure regulator. If the line is wet and smells to fuel, replace the fuel pressure regulator.
- If pressure is within specifications, you can unplug a fuel injector electrical connector and plug in a nod light to the harness connector (you may loan a set of nod lights from your local auto parts store).
- Ask your assistant to crank the engine, while you watch the nod light.
- If the nod light flashes while the engine is being cranked, you can at least assume that the injectors are receiving the pulse signal from the computer. If not, you need to check for a blown fuse or bad relay in the fuel injection system, a problem with the computer control, or problems with input sensors (for example the crankshaft or camshaft position sensors). Scan your computer for trouble codes. Refer to the list of related components below.
Some Cars Automatically Shut Off the Fuel Pump After a Crash
Some models, like many Ford vehicles, have a fuel pump switch (inertia switch), that automatically cuts power to the fuel pump when involved in an accident. If your engine refused to start after an accident or after a vehicle struck yours in a parking lot, check for an inertia switch. The switch helps prevent your car catching on fire if an accident occurs. Check your car owner's manual or vehicle repair manual to locate the switch. You can pop the button back in manually.
III. Do You Have Proper Compression?
Compression in the cylinder heats up the air-fuel mixture and helps the spark ignite the mixture so the combustion takes place. During the combustion process, though, there should be no air leaks. Otherwise, the cylinder will have poor combustion, or it will not happen.
The most common source of air (combustion) leak is a jumped timing belt or chain that allows air to escape through a valve; it can also happen because of a burned valve, worn-out compression rings, or a blown head gasket.
A timing belt or chain synchronizes camshaft to crankshaft rotation. After miles of service, it wears down, becomes damaged, or breaks. So car manufacturers suggest replacing a timing belt every five years. A timing chain may have a wider service schedule interval. Replacing the belt or chain at the suggested interval can prevent serious engine mechanical problems. Consult your vehicle repair manual.
On some vehicle models, it is easy to remove the timing cover to check if the belt or chain is still in place. If it is, you may be able to visually inspect the belt or chain condition, and then check that it hasn't jumped. Follow the instructions in your vehicle repair manual.
Likewise, you can check compression pressure using a compression gauge. If you have a gasoline engine, you screw the gauge into a spark plug hole; on diesel engines, screw the gauge in place of a glow plug or injector nozzle. Follow the instructions in your vehicle repair manual.
Gasoline engine compression ranges from 130 to 180 pounds per square inch (psi); diesel engine compression may range from 250 to 400 psi.
Nine More Components That Can Cause Crank-No-Start
Other Components That May Cause a No-Start Condition
Faults in other systems, not just ignition, fuel, or compression problems, can prevent your engine from starting. A system component itself may be faulty, or there may be a problem with its wire connector or harness. You may need to expand your diagnostic procedure to the components below.
Computers in modern vehicles monitor many of these components (usually in emission-related systems) and can set trouble codes when problems arise. So don't forget to scan your computer.
The exhaust gas recirculation (EGR) valve introduces a measured amount of exhaust gases into the intake manifold to get re-burned. This helps lower engine temperature and harmful emissions. But the valve can fail and stick either open or closed. When the valve sticks open it may prevent your engine from starting. Other symptoms of a stuck-open EGR valve include rough idle and stalling.
2. Cold Injector
Some vehicle models use a cold-start injector. It operates as a regular injector, but only works when the engine is cold. The injector may have its own thermo switch or may be commanded by the system control module. If either the switch or the computer circuit fails, you may have a hard time starting the engine during cold months. Consult your vehicle repair manual, if necessary.
The manifold absolute pressure (MAP) sensor compares the barometric (atmospheric) pressure to the intake manifold vacuum. When the sensor fails, it can prevent your engine from starting. Not all vehicles use this sensor. Consult your vehicle repair manual.
The mass air flow (MAF) sensor tells the computer the amount (the density) of the air entering the engine. A common MAF problem is dirt or foreign matter blocking the sensing element, preventing the sensor from working. Or the sensor itself may fail after miles of service. You can clean and test the sensor at home.
The computer uses the engine coolant temperature (ECT) sensor to know how much fuel the engine needs and when to enter closed loop operation (that is, when the engine has reached operating temperature). Depending on your particular model, a bad ECT sensor can upset ignition timing, or the operation of the transmission or cooling fan. Consult your vehicle repair manual, if necessary.
6. Canister Vent Valve
The canister vent valve is part of the evaporative emissions control (EVAP) system. The EVAP system temporarily stores harmful fuel vapors into a canister to prevent their release into the atmosphere. When conditions are appropriate, the computer routes the fuel vapors out of the canister through a canister vent valve and into the intake manifold for burning. A faulty valve, though, can prevent the engine from starting. Consult your vehicle repair manual for the procedure to test the valve.
The throttle position sensor (TPS) monitors the position of the throttle valve. It sends a voltage signal to the computer. The computer uses this information to regulate the air-fuel mixture according to engine needs. On some vehicle models, a worn out, failing or bad TPS will prevent your engine from starting at all.
8. Vacuum Leaks
Vacuum leaks are not uncommon, and they are the source of many engine performance problems, including fail to start. Depending on where the fault is located, vacuum leaks can be hard to find. But mayor vacuum leaks that can make the engine hard to start may happen in the power booster vacuum hose, EGR valve, another main vacuum hose or a blown head or intake manifold gasket.
If you have an old vehicle model with a carburetor, double check that the fuel level is properly adjusted. If the carburetor is flooded, you'll probably perceive a strong fuel odor under the hood. A little trick you can use is to fully depress the accelerator and try to start the engine. If the engine doesn't start, wait for a few minutes and try again.
When your engine cranks but fails to start, it can be difficult to fix if you don't know where to begin troubleshooting. This guide not only tells you where to start but helps you build your diagnostic strategy. And reminds you of some simple but easy to forget places to look into. So most of the time, using just this guide you'll be able to zero in on the problem.