The starting issues with this thing run way deeper than just glow plugs and some wires. It has to be plugged in to start whether the temperature is 9 or 90. I've tried getting some theories on here before and the best I've come up with is injectors. Something called a poppet valve. Everything else has been replaced at least once by the previous owner. I'm just about ready to buy a fuel injector "super kit" from Diesel Care Products in Tennessee and do it all and then I'll know what's done.

 

If the injectors are worn too much, they don't flow high pressure oil properly, which is the mechanism used to spray the fuel. Think of them like a spray bottle of fuel and the oil is what squeezes the trigger when the electrical signal turns on the green light.

Plugging in heat and THINS the oil, which then flows better, sometimes allowing marginal or sticky injectors to work, sort of.

It's also possible the injector orings can be leaking, which separates the oil from the fuel. This causes the high pressure oil to leak off (giving a weak spray of fuel, which is harder to ignite) and can leak oil into the fuel/cylinder. The oil will burn when the cylinder is hot (engine is running), but it impedes starting initially as it isn't as easy to ignite as diesel fuel.

How many miles are on these injectors? As they get high miles, the parts wear out. If they are say 250k or less, maybe try replacing the injector orings. Just be ready to evaluate the injectors when they are out to see if they need replaced. You'll clean them up a bit and replace the orings, which helps with the leaking and fuel contamination with oil.

You can also try running Rotella T6 5w-40w diesel oil. It already has thinner components in it, which is why many of us run it in the winter- cold oil is thicker, so the "thinner" makes easier starts. Not actually thinner, just flows better

Replacing an entire harness (instead of injector harness/UVCH), is a MAJOR and very unusual thing. Unless it has sustained major damage from a fire or vermin infestation.

Hope this helps a bit.

 

Maybe you could post some pictures of the damage/issues you are having so that some of the FTE experts can provide advice. Like ExPACamper said, changing out the entire main harness is not something you see everyday and is very unusual.

 

The motor has 200k on it. I could pull out an injector and look at it and couldn't tell a good one from a bad one if my life depended on it.

 

I didn't mean for you to pull injectors, sorry for the miscommunication. I meant if you could get a picture of the bad wire that you are talking about and post it here, some one from FTE would certainly be able to tell you if there was a cheaper fix than $500.

If I am misunderstanding your problem, then ignore the words I have written.

 

Yeah... I've read everything here, and I'm not seeing a concise description of the part or the problem. We really need a picture of the harness that you feel the bad.

If I'm reading this correctly... you have a short wire harness to the outside connector on one of the valve covers, and you have a cold-start problem.

UVCH link in my signature may or may not help here, and search the forum for the terms "Glow Plug" and "Glow Plug Relay" for tests you can conduct with the GP system. There are more links in my signature that can help with stubborn 7.3Ls.

 

Sous - sorry, that was a partial reply to ExPA that I managed to post without finishing. He had mentioned pulling injectors to check o-rings and such.

It was suggested to cut out the damaged pigtail, solder on a longer glowplug lead to the single wire in the harness and then attach the 4-14 gauge wires to the new lead. Hopefully that will help on that end. The injectors are a separate but related problem.