Q: My car wont crank

If the car was frequently making a jerking reaction and is now not starting at all, this may be related to many different things, however this is a common symptom of a camshaft position sensor that may have been failing and has finally completely failed. The camshaft position sensor measures the rotational position of the camshaft and transmits that information to the engine control computer. To determine which cylinder is in its power stroke, your car’s computer monitors the rotating position of the camshaft relative to the crankshaft position using a camshaft position (CMP) sensor. It uses this information to adjust the spark timing and the operation of the fuel injectors. Thus, the CMP sensor affects fuel economy, emissions control, and engine efficiency. The two most common camshaft sensors you’ll see are the magnetic and Hall-effect types. Both transmit a voltage signal to an electronic control module or to the car’s computer. The magnetic type produces its own AC (alternate current) signal (a sine wave), and you can identify it by its two wires. The Hall-effect type uses an external power source to produce a digital signal (a "square wave," on-or-off) and has three wires. Depending on the specific model of your car, your engine may have one or more cam sensors. When the camshaft sensor fails, you may experience the car jerking while losing power or the car may struggle to move faster than ~35-40 mph. The engine may also stall intermittently, produce poor performance, hard starting, surging or fail to produce an ignition spark. I would suggest having an expert from YourMechanic come to your location to diagnose and inspect your vehicle.