why does my car crank but not start
Whatвs causing the no-start? All engines require three things to start and run: spark, fuel, and compression. If any one of these isnвt there, you arenвt going anywhere. Chances are the Check Engine Light is not on, but you may find any of the following codes:
No spark due to a bad crank position sensor, a faulty ignition module or PCM, a problem in the ignition circuit (ignition switch, antitheft system, wiring, etc. ), a faulty park/neutral safety switch, a bad ignition coil (only on engines with a single coil ignition), or wet plugs or plug wires (did it rain last night, did you just wash the engine? ) A less common cause is a worn starter that draws so many amps while cranking the engine that thereвs not enough juice left to adequately power the ignition system and fuel injectors. Contributing factors might be a weak battery and/or loose or corroded battery cables. No fuel because of a dead fuel pump, bad fuel pump relay, blown fuel pump fuse, plugged fuel filter or line, or failed PCM injector driver circuit or injector power supply relay. Or, the fuel tank might be empty (donвt believe what the gauge is telling you), or the fuel tank might contain contaminated fuel (water or too much alcohol) or the wrong type of fuel (whoops, somebody put in diesel instead of gasoline).
No compression because the timing belt or chain is broken, the timing belt or chain is loose and jumped out of time, or the overhead camshaft has snapped. A powerful scantool like AutoTap Express DIY can help isolate the root cause by capturing this information as in Figure 8. Figure 8 - Typical parameters to monitor for non-start condition The first step is to determine if itвs a spark, fuel, or compression problem. Hereвs a quick way to find out which of the three is missing. Remove a plug wire, insert a Phillips screwdriver or spare plug piece of bare wire into the plug wire boot and place the end near the engine block (do not hold the plug wire while cranking the engine unless you want a shocking experience). If thereвs a spark when the engine is cranked, it has ignition. The problem is either fuel or compression. If the engine has an overhead cam with a timing belt, loosen the cover over the timing belt and check the belt. If the belt is okay, the problem is no fuel. Listen for the electric fuel pump in the fuel tank to make a buzzing noise when the ignition is turned on (you may have to open the gas cap to hear it). You wonвt hear anything if the pump has died. Diagnostics can now be focused on the fuel pump circuit to determine if the pump, relay or wiring is causing the no start.
If the relay has voltage but the pump isnвt running, youвll probably have to drop the fuel tank to check the wiring connector at the pump. If the problem is no spark, anything in the ignition circuit that creates the spark may be at fault. Use your AutoTap Express DIY to look for an RPM signal from the Crankshaft Position sensor while cranking the engine. A bad Crankshaft Position sensor is a common cause of no starts. The signal from this sensor goes to the PCM or ignition module that switches the ignition coil(s) on and off. If you have an RPM signal, a bad ignition module or PCM may not be switching the coil(s) on and off. Using a voltmeter, check for voltage at the coils with the key on and while cranking the engine. The voltage should be switching on and off. In ignition systems with a single coil and distributor, a bad coil or a cracked distributor cap or rotor can prevent the spark plugs from firing. On multi-coil, distributorless ignition systems and coil-on-plug systems; one coil failure may cause an engine to misfire, but it won't prevent it from starting. Whatвs causing the no-start? All engines require three things to start and run: spark, fuel and compression. If any one of these isnвt there, you arenвt going anywhere.
If your engine does turn over and your car still doesn't start, that's when everything gets harder. P There are way more potential causes for this kind of a no-start. A few areas where these problems can occur include; Fuel Pressure, Camshaft Sensor, Crankshaft Sensor, Ignition Problems, etc. Testing any of these areas can get very technical, so we recommend taking your car in to a good repair shop. Many times, people just start replacing parts and end up spending a lot more money than they would have if they had just taken it in to the shop. If your car will turn over but not start, it could be as simple as a camshaft or crankshaft sensor problem! These sensors give the computer inside your vehicle the information it needs to calculate ignition timing, the amount of fuel that is needed, etc so if these sensors are not working properly, it can cause your car not to start. P If your car won't start, it is very unlikely that there is any major damage. P It is possible that there is internal engine damage, but that is extremely rare. If you suspect that there is a problem with your vehicle, call us at or bring it in to the Pand we will diagnose the problem for you. You want to be sure that there is damage before you spend a ton of money to have it fixed!
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