Causes may include:
* Timing chain stretched, or timing belt skipped a tooth due to wear
* Misalignment of timing belt/chain
* Tone ring on crankshaft slipped/broken
* Tone ring on camshaft slipped/broken
* Bad crank sensor
* Bad cam sensor
* Damaged wiring to crank/cam sensor
* Timing belt/chain tensioner damaged
1. First, visually inspect the cam and crank sensors and their harnesses for damage. If you notice broken/frayed wires, repair and recheck.
2. If you have access to a scope, check the cam and crank patterns. If a pattern is missing, suspect a bad sensor or a slipping tone ring. Remove the cam gear and the crankshaft harmonic balancer and inspect the tone rings for proper alignment and make sure they're not loose or damaged or that they haven't sheared the key that aligns them. If they are properly installed, replace the sensor.
3. If the signal appears normal, then check the timing chain/belt for proper alignment. If it's misaligned, check for a damaged tensioner that may have allowed the chain/belt to slip a tooth or several teeth. Also check that the belt/chain isn't stretched. Repair and recheck.