Crank Timing Sensor

Alright, here is a general question for anyone that may know, or feels like giving their input... all comments are welcome

I need to figure out WHAT the exact function of a Crank Timing Sensor is... I have heard things ranging from its a sensor that just times when the truck is gonna start after you turn the ignition, to versions like... Its function is to time when to release fuel into the fuel lines once you turn the key, or is it just a sensor that tells the truck when to start after crancking for a certian period of time... Please help!

 

Well let me put it this way, it would be the sensor that has something to do with the fuel and the time that it takes the truck to acutally start.... The shop manager at volvo ( go figure) called it a "Cranck Timing Sensor" ... the reason I am asking is I am still working on a big starting problem that my truck has... we have changed just about EVERYTHING that can be changed on the darn thing, fuel pump was changed and the accessory drive in Feb, the fuel filters were changed yesterday, I put on Volvo filters on the darn thing. The fuel filter base is good, steady and clean, all fuel lines have been checked there is no leakage anywhere, hence there is nowhere it could keep getting air in, the check valve was changed just a few days ago, I had my mechanic look at my injectors and try to fine if there is a possibilty that they might be losing prime and that was a negative.... Basically, when I changed my fuel filters yesterday, it kept starting up, like there was never a problem with it, I started it up like 25 times and waited to extended periods of time and every time it started. Then late last night it did not want to start AGAIN... today after letting it sit and coming back to it, IT STARTED sure it took a second longer it was crancking longer but it started without me having to prime it on the prime pump. I am really clueless as to what the heck it could be. The volvo shop did throw that option at me that it could be that CRANCK TIMING SENSOR... and now I am trying to figure out what that sensor is....

 

So in plain English, my cranck timing sensor is not sending the info to the ECM, and the ECM is not injecting the fuel into the engine... Now here is my next question when I prime it with the prime pump and build the pressure in the engine the cranck sensor i assume then is not used to send the message to the ECM since I have already build the presure (injected the fuel) into the engine? Is my understanding correct? Oh and my mechanic has already checked the wiring on my batteries and the whole wiring system because that was one of his first assumptionss...

 

Yes they have checked everything... All is good which is the reason why we all are so puzzeled on this one... but then again, its a Volvo... it is so wired as to how it acts, when it wants it will cranck as many times as you want it to cranck with no problems, and when it dont want to, it just does not, and you cannot and will not start without me purging and priming it with the prime pump... its driving all of us INSANE... and once its started it runs and drives PREFECT... there is not loss of power, no shacking or acting up, currenctly I am pulling a 40 000 lbs load at 67mph and its acting perfect, the only issue is it actually starting when I turn the key and ignition....