My buddy has an 03 reg cab dually and he just put the air dog system on it be cause the truck had a hard time starting and it still won't start so what could be the problem now. he isn't throwing any codes

 

I've dealt with this situation multiple times, normally injectors. If not could be a leak on the low pressure system causing a loss prime!

 

how do i fix the low pressure system also were thinking its a vacuum leak

 

make sure your draw straw is in the fuel and whats the rail reading

 

07redsled has given you some good advice, We need some in depth details of what the fuel system is doing. Fuel volume and decay test, Fuel pressure test,Fuel restriction test, Rail pressure, Codes, Oil condition and some stuff like this. At that point we'll put you in the dirrection of test associated with injector failure or another area. The fuel system is affected in no way besides the vaccum created from fuel restriction or the lack of fuel flow to the CP3. The diesel requires no vaccum , and creates no vaccum. It's a turbocharged engine, if your thinkin somthing like a line loose!

 

That's correct, no vacuum on these trucks as everything, even the hvac is operated electronically by solenoids and motors. The draw straw should be the stocker on the 03 as the original lift pump that the air dog replaced is on the back of the filter housing. Hard start on the 03 is a wide spread problem. A couple of things to look at are the injector harness as it passes under the aluminum valve cover. Sometimes these wires fray and become broken. Also, on the passenger side of the engine compartment there is a harness that passes over the A/C that becomes worn through. It is the cam positioning sensor wire. Also, there is a flash update at the dealer for hard starts but it is really hit and miss. Do you know about the key on key off trick to retrieve codes from the ECM? If not here goes, you turn the key on and then off three times without starting the vehicle. On the third time, you end with the key in the on position. In the odo window you will see some codes appear if any are present. Have a piece of paper and pen ready to write them down and report them here. If no codes are present then the word done will appear and then some hash marks and then the odo reading.

I'll see what else I can dig up.