What To Do When Your Car Won't Start Every engine requires four basic ingredients to start: sufficient cranking speed, good compression, adequate ignition voltage (with correct timing) and fuel (a relatively rich air/fuel mixture initially). So if your car fails to start, you can assume it lacks one of these four essential ingredients. But which one? To find out which thing is missing, you need to analyze the situation. If the engine won't crank, you are probably dealing with a starter or battery problem. Has the starter been acting up? (unusual noises, slow cranking, etc.). Is this the first time the engine has failed to crank or start, or has it happened before? Have the starter, battery or battery cables been replaced recently? Might be a defective part. Has the battery been running down? Might be a charging problem. Have there been any other electrical problems? The answers to these questions should shed some light on what might be causing the problem. If an engine cranks but refuses to start, it lacks ignition, fuel or compression. Was it running fine but quit suddenly? The most likely causes here would be a failed fuel pump, ignition module or broken overhead cam timing belt. Has the engine been getting progressively harder to start? If yes, consider the engine's maintenance and repair history. NO START DIAGNOSIS What happens when you attempt to start the engine? If nothing happens when you turn the key, check the battery to determine its state of charge. Many starters won't do a thing unless there is at least 10 volts available from the battery. A low battery does not necessarily mean the battery is the problem, though. The battery may have been run down by prolonged cranking while trying to start the engine. Or, the battery's low state of charge may be the result of a charging system problem. Either way, the battery needs to be recharged and tested. If the battery is low, the next logical step might be to try starting the engine with another battery or a charger. If the engine cranks normally and roars to life, you can assume the problem was a dead battery, or a charging problem that allowed the battery to run down. If the battery accepts a charge and tests okay, checking the output of the charging system should help you identify any problems there. A charging system that is working properly should produce a charging voltage of somewhere around 14 volts at idle with the lights and accessories off. When the engine is first started, the charging voltage should rise quickly to about two volts above base battery voltage, then taper off, leveling out at the specified voltage. The exact charging voltage will vary according to the battery's state of charge, the load on the electrical system, and temperature. The lower the temperature, the higher the charging voltage. The higher the temperature, the lower the charging voltage. The charging range for a typical alternator might be 13.9 to 14.4 volts at 80 degrees F, but increase to 14.9 to 15.8 volts at subzero temperatures. If the charging system is not putting out the required voltage, is it the alternator or the regulator? Full fielding the alternator to bypass the regulator should tell you if it is working correctly. Or, take the alternator to a parts store and have it bench tested. If the charging voltage goes up when the regulator is bypassed, the problem is the regulator (or the engine computer in the case of computer-regulated systems). If there is no change in output voltage, the alternator is the culprit. Many times one or more diodes in the alternator rectifier assembly will have failed, causing a drop in the unit's output. The alternator will still produce current, but not enough to keep the battery fully charged. This type of failure will show up on an oscilloscope as one or more missing humps in the alternator waveform. Most charging system analyzers can detect this type of problem. ENGINE CRANKING PROBLEMS If your car won't start because the engine won't crank or cranks slowly (and the battery is fully charged), you can focus your attention on the starter circuit. A quick way to diagnose cranking problems is to switch on the headlights and watch what happens when you attempt to start the engine. If the headlights go out, a poor battery cable connection may be strangling the flow of amps. All battery cable connections should be checked and cleaned along with the engine-to-chassis ground straps. Measuring the voltage drop across connections is a good way to find excessive resistance. A voltmeter check of the cable connections should show no more than 0.1 volt drop at any point, and no more than 0.4 volts for the entire starter circuit. A higher voltage drop would indicate excessive resistance and a need for cleaning or tightening. Slow cranking can also be caused by undersized battery cables. Some cheap replacement cables have small gauge wire encased in thick insulation. The cables look the same size as the originals on the outside, but inside there is not enough wire to handle the amps. If the headlights continue to shine brightly when you attempt to start the engine and nothing happens (no cranking), voltage is not reaching the starter. The problem here is likely an open or misadjusted park/neutral safety switch, a bad ignition switch, a bad Start Engine Push Button or a faulty starter relay or solenoid. Fuses and fusible links should also be checked because overloads caused by continuous cranking or jump starting may have blown one of these protective devices. If the starter or solenoid clicks but nothing else happens when you attempt to start the engine, there may not be enough amps to spin the starter. Or the starter may be bad. A poor battery cable, solenoid or ground connection, or high resistance in the solenoid itself may be the problem. A voltage check at the solenoid will reveal if battery voltage is passing through the ignition switch circuit. If the solenoid or relay is receiving battery voltage but is not closing or passing enough amps from the battery to spin the starter motor, the solenoid ground may be bad or the contacts in the solenoid may be worn, pitted or corroded. If the starter cranks when the solenoid is bypassed, a new solenoid is needed, not a starter. Most engines need a cranking speed of 200 to 300 rpm for your car to start, so if the starter is weak and can't crank the engine fast enough to build compression, the engine won't start. In some instances, a weak starter may crank the engine fast enough but prevent it from starting because it draws all the power from the battery and does not leave enough for the injectors or ignition system. If the lights dim and there is little or no cranking when you attempt to start the engine, the starter may be locked up, dragging or suffering from high internal resistance, worn brushes, shorts or opens in the windings or armature. A starter current draw test will tell you if the starter is pulling too many amps. A good starter will normally draw 60 to 150 amps with no load on it, and up to 200 amps or more while cranking the engine. The no load amp draw depends on the rating of the starter while the cranking amp draw depends on the displacement and compression of the engine. Always refer to the OEM specs for the exact amp values. Some "high torque" GM starters, for example, may have a no load draw of up to 250 amps. Toyota starters on four-cylinder engines typically draw 130 to 150 amps, and up to 175 amps on six-cylinder engines. An unusually high current draw and low free turning speed or cranking speed typically indicates a shorted armature, grounded armature or field coils, or excessive friction within the starter itself (dirty, worn or binding bearings or bushings, a bent armature shaft or contact between the armature and field coils). The magnets in permanent magnet starters can sometimes break or separate from the housing and drag against the armature. A starter that does not turn at all and draws a high current may have a ground in the terminal or field coils, or a frozen armature. On the other hand, the starter may be fine but can't crank the engine because the engine is seized or hydrolocked. So before you condemn the starter, try turning the engine over by hand. Won't budge? Then the engine is probably locked up. A starter that won't spin at all and draws zero amps has an open field circuit, open armature coils, defective brushes or a defective solenoid. Low free turning speed combined with a low current draw indicates high internal resistance (bad connections, bad brushes, open field coils or armature windings). If the starter motor spins but fails to engage the flywheel, the cause may be a weak solenoid, defective starter drive or broken teeth on the flywheel. A starter drive that is on the verge of failure may engage briefly but then slip. Pull the starter and inspect the drive. It should turn freely in one direction but not in the other. A bad drive will turn freely in both directions or not at all. ENGINE CRANKS BUT YOUR CAR WILL NOT START When the engine cranks normally but the engine won't start, you need to check ignition, fuel and compression. First, check the fuel gauge. Is there fuel in the tank? Your engine will not start if there is no fuel in the tank. Ignition is easy to check if you have an older engine with spark plug wires. Remove one of the plug wires from a spark plug and position the end near a good ground. Have a helper crank the engine while you observe the end of the plug wire for a visible spark. CAUTION: Do NOT touch the plug wire while the engine is cranking or you may be shocked!. No spark? The most likely causes would be a bad ignition coil, failed ignition module, distributor pickup or crankshaft position (CKP) sensor. On newer vehicles with multi-coil ignition systems (a separate coil for each spark plug and no high voltage spark plug wires), checking for spark is more difficult. A quick way to see if the ignition system is generating sparks …

Fonte: AA1Car.com