8120 cranking but not starting

Thank you to Henry at Norsask. 8120 was cranking but not starting today. Think it was called the "phonic wheel" on the timing gear slipped. We're at a loss as to why combine wouldn't start but would crank. Thought old batteries woth weak voltage. No help. Good fuel to injectors. Was going to try filters anyways. Quick check unplugging sensor and combine ran. Took off front engine cover and repositioned "phonic wheel" to original marks. Runs like a charm.