PDA

View Full Version : desiel won't run


FU Toolbag
11-17-2008, 11:38 PM
I pulled a 7.3 out of my old dd and it's been put into a van that had a 6.9. I switched over the oil cooler, glow plug circut, and fuel filter setup. The thing will fire up, no majour problem. Runs for about 15-25 seconds, then dies. You can't fire it up again for several minutes, but when it does, same thing. It's so pissing me off. Any ideas? Anything at this point would help. I'm running out of hair to pull out. I've never had a motor swap this bitchy.

SquirreL-E
11-18-2008, 12:13 AM
cold start? haha, our 7.3 does that at work when its cold, but all i was told to do was hold the gas pedal half on for starting, and let it run at 1500-2000rpm for a bit just to let it heat up that little bit, or plug the thing in block heater =D

Reeseman
11-19-2008, 04:23 PM
you could be drawing in air in the fuel somewhere check the fuel lines make sure everything is tight.

sj-x 500
11-19-2008, 09:33 PM
sounds like a loose fuel filter/suction side hoses.

degsey
11-19-2008, 10:00 PM
make sure your fuel filters primed properly ie fill to the top with fuel , crack your injectors spin the engine over till u get fuel coming out to make sure there is no air in the system at all. i usually start with one injector at a time. good luck

Tha_Stepside
11-19-2008, 10:11 PM
make sure your fuel filters primed properly ie fill to the top with fuel , crack your injectors spin the engine over till u get fuel coming out to make sure there is no air in the system at all. i usually start with one injector at a time. good luck

I agree, and check your fuel pressure at the injectors. Im not sure if the old 7.3/6.9 use a scavenger pump as well for the fuel system. Start from where the fuel comes out (i.e. injectors) then work your way back to the tank testing fuel pressures all the way. Or like degsey said, start with your #1 firing cylinder, crack it open and see if you are getting fuel. We have V16 diesels at work and its a common problen for the scavenger pump to only feed enough fuel to the filter or pump then after the resudual fuel is burned off the engine simply wont run because the pump cant produce enough fuel to keep the engine running. Whatever it is it is definitely a fuel problem.

FU Toolbag
11-19-2008, 10:40 PM
I've already checked all that. lots of volume and lots of pressure. Good flow going to the return lines.


Was rather surprised when I found out today that there is a checkvalve in the injectors that can go bad, allowing the pressure from the compression stroke to puch the fuel and air back into the pump. That's why it'll run, only for a little bit, then when running, it dies. Never concidered that even possible, but apperantly it happens. We're checking that tommorow. Gotta disconect all the lines, disconect wires to pump cellinoids and spin the motor. Whichever ones blowing get's changed. Are the 7.3 injectors the same as the 6.9's?

Tha_Stepside
11-21-2008, 05:42 PM
Good call, im not too sure wether the 7.3 squirters are the same, but if you have a failing check valve that could definitely cause a problem. But as soon as that checkvalve gives up (i would imagine as soon as presure builds into the fuel system) it wouldnt even allow enough pressure in the injector to provide adequate atomization for cumbustion. If you have the resources, take one of your injectors (start at #1) out of the system, hook it up to an injector tester and spray it onto a piece of paper or cardboard. You should have a circular pattern thats really dense and a light coating in the middle, if your checkvalves are working then you should be able to build up enough pressure in the injector to make a good squirt. Any heavy-duty shop can test your injectors for you for minimal charge as long as you have them numbered and off the truck. Good luck and let us know what happens.

sj-x 500
11-21-2008, 08:13 PM
no one does that anymore. mechanical injectors are so cheap it's not worth the hastle to remove, test, and reinstal. and that test doens't really prove they would be leaking back, just would be able to see if they are pumping, the problem would be at the injection pump end pretty much right whre it comes out of the pump, it's called a delivery valve.