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Sounds like you may have problems with the Under Valve Cover Harness(es) that feed the injectors and glow plugs. The proper way to diagnose it is to do an Injector Buzz test with a PSD capable scan tool, but you can find out without it. If you take the exterior Valve Cover harness connector loose, you can use an ohmmeter to check continuity thru the injector solenoids. The center pin is common to all injectors and the two directly in front of center feed the two front injectors and the two directly in back of center feed the rear injectors. The frontmost 2 and rearmost 2 pins go to the glow plugs. Measuring between the center pin and one of the injector feed pins, you should get 5 ohms or less. Do that for all 4 injectors on each side. If you get infinite resistance, you have an open in that circuit under the valve cover. Then you'll know which VC to remove (maybe both, but unlikely). If you find the UVC harness loose, replace it with a new one, about $25 from International, part #1830844C93. If you take the VC off and ohm out the injector solenoids individually and find any that are open, you'll at least have to replace the solenoid on that injector.
You can do the job with common hand tools, even if it comes to pulling an injector. If you get to that, check on Swamps Diesel Performance website
for instructions for injector R&R
Hope that helps