1999 yukon changed everything even the timing chain and it still wont start, new dist.new coil and mod.new throtel position and acumulator

have you checked the oil pressure sending unit switch?

You have spark at the plugs right? Have you checked fuel pressure? It has to be 60 psi or it won't even fire.

okay, did you have these items out of motor or did it quit running and this is what you have checked? I can fix this problem but i dont know where to start with this information. I can say that the crank has to be at zero,the #1 piston needs to be at TDC( up in cylinder) the cam sprocket has a mark that should align up with crank, the dist rotor should aim to #1 cylinder and the dist cap position wire should go to the #1 spark plug, If this was all in tack and now the truck wont start and this is your diagnosis then i would check the timing chain and gear for worn or nylon broken timing gear . If you put this together and you noticed this then you can either remove dist and align oil pump shaft and re-install or move the plug wires one post starting with the rotor aim as the #1 wire and proceed in a clockwise rotation 1-8-4-3-6-5-7-2 . As long as the dist can move for timing purposes it doesnt mater where the #1 wire starts as long as the #1 wire starts where the rotor aims and the motor is in time. If everything was in tack then the chain has jumped and needs replaced.

THERE IS A PICKUP COIL IN THE DISTRIBUTOR, IF YOU HAVEN'T CHECKED THAT, IT IS PROBABLY EASIER TO CHANGE THE DISTRIBUTOR THAN TRYING TO CHANGE JUST THE PICKUP COIL. MAKE SURE THE PICKUP COIL COMES IN THE NEW DISTRIBUTOR BEFORE YOU BUY. THE PICKUP COIL OFTEN CAUSES THE PROBLEM YOU ARE HAVING WITH YOUR CAR

Check to make sure the coil wire is secured to the distributor cap and rotor.
Also check that the rotor is not cracked (even if new) and that the spark plugs are not loose - wires are not loose, frayed etc.
Also, make sure all connections on the battery, ground at chassi, and positive on starter are in good repair as well.
Please, let me know if you need further assistance.
carsandcomps,
Guru, Premium Expert @ Fixya.com

1/ Have you fitted the spark plug leads in the proper firing order.
2/ Look inside the top of distributor Top (this is not the first time a new distributer cap has very small crack) or the rotor arm is fitting the cap properly. Hope this helps Best Wishes, Malcolm Campbell.

check the fire to the coil pack if it's present then check the pulse to the crank sensor

There may be no injector pulse if the computor does not see a RPM signal.
There will be no spark if the ignition module does not see a dist pulse from the dist pickup.......a RPM signal.
Because you do not have both ......I would suggest to check/change the dist pick up.
Follow the wires from the ignition module inside the dist to the pickup which is also inside the dist.
If it is just a bad dist pickup....keep all your old parts as good spares.
Also...is the dist turning? to provide a RPM signal?
You will have to remove the dist to change the pick-up.....mark your timing locations......"rotor position" and "dist body location"before removal.
A quick test before installing the "repaired dist" .....plug it in the the truck wiring and turn on the key....DO NOT CRANK THE ENGINE OR YOU WILL LOSE YOUR DIST ROTOR CORRECT POSITION......as you spin the dist by hand .....the injectors should spray.

check timing belt!! good luck!!

Check your spark plugs and see if they need to be replaced. Check the gap on the spark plug. You may have low compression, timing belt or chain should be checked as well. Check the computer system in your car. Is your check engine light on? Maybe your crank sensor is not working properly. Try these and if not get back to me and we'll try more possibilities.