Q: Q: Engine cranks, but won't turn over

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When I turn the ignition key, car engine will crank but not turn over to start. Earlier in the day, car would jerk while accelerating from a complete stop. Also, while decelerating, there is a slight hesitation in the car automatically downshifting. I have replaced the throttle body about 2 months ago. I was thinking it could be the fuel pump?

My car has 143000 miles.
My car has an automatic transmission.

A number of things may cause the truck not to start, however it sounds like you may have a faulty camshaft position sensor based on what you are describing. 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.

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