Do you need a new starter because your engine won't crank? Many starters are replaced unnecessarily and are later returned back to the parts store because they are thought to be defective. When tested, there's no fault found. The real problem is misdiagnosis. Professional technicians will usually make the correct diagnosis, but many DIYers are simply making a semi-educated guess – and they sometimes guess wrong. One of the best ways to find out if your starter is bad is to have it "bench tested" at a parts store. If it cranks at normal rpm under load, the problem is something else. Replacing the starter won't fix your problem. If it fails to crank, the starter needs to be replaced. When you buy a new or rebuilt starter, compare the old and new units to make sure the replacement starter is the correct one for your vehicle. Is the mounting surface and bolt configuration the same? Is the flywheel gear the same (count the teeth if you're not sure). Does the replacement starter have the same electrical connections? Because most of the starters that are sold in the aftermarket today are remanufactured units, you can usually exchange your old starter for a partial credit against the price of the new starter. If your old starter has been disassembled, has parts missing or has a cracked case, you may not receive full credit (or any credit) for your old unit. Rebuildable cores for many late model vehicles are valuable, so make sure you get full credit for the exchange. STARTER DIAGNOSIS: ASK THE RIGHT QUESTIONS What happens when you turn the key and try to start the engine? If the answer is, "Nothing," you should check the battery, battery terminals, battery cables and ignition circuit to make sure voltage is reaching the starter. If the battery is low or has corroded terminals or loose cable connections, the starter may not crank because of low voltage. If the solenoid that energizes the starter motor is faulty or has loose electrical connections, it will prevent the starter from cranking, too. A faulty ignition switch, park/neutral safety switch on the transmission linkage, clutch safety switch on the clutch pedal or a wiring problem are other faults that can also prevent a starter from cranking. TYPES OF STARTERS Starter motors come in several varieties. Most older vehicles have a rather large, heavy starter motor that has field coils around an armature. On newer vehicles, the size of the starter motor has been downsized either by using permanent magnets in place of field coils, or by using reduction gears to multiply the torque produced by a smaller motor. As a rule, permanent magnet and gear reduction starters are more expensive units to replace. Permanent magnet starters must also be handled with care because the magnets can be easily cracked and ruined if the starter is dropped on a hard surface. STARTER PROBLEMS Starter problems can be caused by worn brushes (carbon pads inside the motor that supply current to the rotating armature), by shorts or opens in the armature or field coils or by worn bushings that increase drag or allow the armature shaft to rub against the pole shoes. Continuous and prolonged cranking is very hard on a starter motor because it generates excessive heat. If not allowed to cool down every 30 seconds or so for at least a couple of minutes, the starter will be damaged by continuous cranking. You should have your old starter bench tested to determine if it needs to be replaced. Using a battery and a pair of cables to jump the starter will only tell you if it spins, not how many amps it is drawing or how fast it is cranking. To accurately test a starter, a test stand that can measure amp load, voltage and rpm is required. A good starter will normally draw 60 to 150 amps with no load on it, and up to 250 amps under load (while cranking the engine). The no load amp draw will vary depending on the type of starter. If the amp draw is too high, the starter needs to be replaced. The same is true if the starter doesn't achieve the specified rpm. Excessive starter draw can be caused by high resistance within the starter itself, worn brushes, or grounds or opens in the armature or coil windings. It can also result from increased internal friction due to shaft bushings that bind or an armature that is rubbing against the housing (if the starter is noisy, it's probably dragging). Sometimes the starter motor works fine but the drive gear won't engage the ring gear on the flywheel. If the drive gear mechanism can be replaced separately, there's no need to replace the entire starter. A bad solenoid can also cause starter problems. The solenoid acts like a relay to route power directly to the starter from the battery. It may be mounted on the starter or located elsewhere in the engine compartment and is usually connected to the positive battery cable. Corrosion, poor ground at the solenoid mount or poor battery cable connections will prevent the solenoid from doing its job. If the starter tests okay but fails to crank, another possible cause may be a bad ignition switch, neutral safety switch or clutch safety switch. A low battery and/or loose or corroded battery cables can also prevent the starter from cranking the engine. CHARGING SYSTEM OPERATION The charging system consists of an alternator (that generates electricity), a voltage regulator (that controls the alternator's output) and the battery (that stores amps). The charging system's job is to keep the battery fully charged, and to supply voltage to meet the vehicle's electrical needs. Cranking an engine pulls amps out of the battery. These must be replaced, or over time the battery will eventually run down each time the engine is started and driven. As soon as the engine starts, the charging system automatically senses the need for amps and starts recharging the battery. It also produces as many additional amps as are needed to keep the ignition system, fuel injectors and electrical accessories running. As a rule, the charging voltage is about two volts higher than battery voltage. TYPES OF ALTERNATORS There are zillions of different OEM part numbers for alternators, so aftermarket suppliers try to consolidate applications as much as possible. What's really important is how the alternator is wired (A-circuit, B-circuit or I-circuit), the type of voltage regulation (external regulator, internal regulator or computer-controlled regulation) and the physical hookups (bolt hole locations and indexing, wiring connectors and pulley dimensions). Alternators with type "A" circuits have an externally grounded field. One brush is connected to positive battery voltage, and the regulator switches between field and negative to control output. Type "B" circuits have an internally grounded field with one brush connected to battery negative and the regulator switching between field and positive to control output. A third type of circuitry that is used less often is the "I" type. This configuration has an insulated ground system. In addition to the normal armature terminal that serves as the charge output terminal, it has a second armature terminal normally marked "A2" that serves as the ground return. This type of unit works like an "A" circuit unit and is tested and polarized in the same way, except that the "A2" terminal is used instead of the "A" terminal. When an A-circuit regulator loses positive voltage, the alternator will overcharge if the field still has power. If the regulator loses its power. If the regulator loses its ground, the system will go dead. With B-circuit systems, just the opposite is true. If a B-circuit regulator loses its ground, the alternator will run wild and overcharge. If it loses positive voltage, the alternator will go dead. A replacement alternator doesn't necessarily have to look the same as the original, but it must function the same electrically, have the same pulley dimensions and be a bolt-in replacement. With consolidated applications, it is sometimes necessary to modify or change the wiring connectors as well. CHARGING SYSTEM & ALTERNATOR DIAGNOSIS Most charging systems that are working properly should produce a charging voltage of about 13.8 to 14.3 volts at idle with the lights and accessories off. Always refer to the vehicle manufacturer's specifications. Many Asian vehicles can have higher charging voltages (up to 15 volts). 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 vehicle's electrical system, and temperature. The lower the temperature the higher the charging voltage, and the higher the temperature the lower the charging voltage. The "normal" charging voltage on a typical application might be 13.8 to 14.3 volts at 77 degrees F. But at 20 degrees F. below zero, the charging voltage might be 14.9 to 15.3 volts. On a hot engine on a hot day, the normal charging voltage might drop to 13.5 to 14.3 volts. Charging output of the alternator can also be checked with an adjustable carbon pile, voltmeter and ammeter. The carbon pile is attached to the battery and adjusted to obtain maximum output while the engine is running at 2000 rpm. Charging amperage is another number that can reveal the condition of the alternator. With the engine idling and no load on the charging system (lights and all accessories off, battery fully charged), the amperage output should be relatively low (typically less than 10 amps). With the headlights and heater blower fan on and the engine running at 2000 rpm, the output should jump to a higher reading, typically 25 to 30 amps or more. Warning: Never disconnect a battery cable while the engine is running to "test" the alternator. Doing so can cause high voltage spikes that can damage the alternator as well as other electronics. NOTE: If a vehicle has a history of repeat alterna…

Fonte: AA1Car.com