Ok, I have a gremlin...truck is a 2003 W900L with a 6NZ Cat.

On start up, the truck will fire usually without a hitch. Every now and again I can crank on it until the starter burns up and it won't start, but if I turn the key back off I can immediately turn it over again and it will start. Usually what happens is it will start, run for a few seconds, die as if I turned the key off, then catch itself right before it stops turning. After that it purrs like it should. Now, every now and again I can fire it up and it will not die out. Sometimes while idling after a little bit, it will stutter a little, clear its throat, then smooth out again. On occasion, it will die completely while moving. So far, that has only happened at low speeds like crawling through the trailer yard at 10mph. It died, I restarted it, moved about 50 feet, it died again. Not getting any codes. When it dies, all of the electronics (dashboard, radio, cb, etc.) stay on without interruption. One of my drivers said the check engine light would flash on occasion when he went to Georgia last week, but it quit before he made it back and again I could not recover any codes. He said it ran like a top the whole trip.
I have checked the fuel pressure, checked the fuel lines, replaced the filters, checked fuel line connections to make sure they are tight, replaced the check valve at the secondary filter housing, replaced the fuel pump, checked fuses, checked battery connections, replaced the ignition switch, checked the wires to the ignition switch, started it and wiggled every wire I can find from the battery box to the starter to the ecm to the frame rails to the engine harness, behind the dashboard, etc... I am absolutely stumped and tired of chasing this thing. Thoughts?

 

Well, I forgot to mention I also put in a bunch of sensors. Cam, crank, and fuel pressure sensors are maybe a year old, oil pressure, boost pressure, and air intake temp sensors are brand new. New wiring harness from ECM to the sensors, too. Atmospheric sensor maybe...? I'm so lost at this point I'm just throwing sh** at the wall to see what sticks...

 

I guess I could replace the cam and crank sensors again, but like I said the ecm to engine harness is brand new. And I have traced every wire i can think of and no luck. Not to say I couldn't have missed something, I don't pretend to be the greatest mechanic in the world.

 

Are you talking about the cab to ECM harness or the ECM to engine harness?