That is a schrader valve for bleeding the air. Personally, I only use it to see if I have air in the lines when diagnosing hard starts. The best way to bleed the lines, is by cracking open injector lines one at a time. Did you fill up the fuel filter when you installed it? That could be working against you. Does your voltage gauge drop when cycling the GPs?
It was starting immediately everytime. Then one day when I tried to start it, the glow plug relay would click but the truck would not start. Then the water pump started leaking so I took it to a mechanic in town to replace the waterpump and I also told the mechanic that the relay was clicking but the truck wouldl not start. I hauled it into town on my trailer to the mechanic. Anyway the mechanic called me and told me that the problem was the batteries were not good so they removed and replaced the batteries with new ones and he said it now starts good. When I went to get it, it started but not immediately, I had to crank on it a while before it started. I then drove it home. Later when I started to use it, I noticed that it took a while to start, it would not start immediately like it used too. Then the second time I tried to start it at home it would not start at all, and it has been sitting there ever since. I am retired now but as a young man I was a gasoline mechanic so I thought, I can fix this thing myself so this is where I am at now, trying to figure out what went wrong with my 6.9 that it won't start. I am begining to think maybe it has air in the system. The mechanic in town put a new fuel filter on it, maybe he did not fill up lthe filter. I will take the filter off and see if it is full of fuel, maybe thats my problem.
At this point, the filter has been filled since it was running, but it would still be a good idea to remove the filter. If it is not %100 full, then you have air intrusion problems which are very common with these engines. You will have to let it sit overnight before checking the filter.
Forget air, batteries, and all of the other things. This, right here is the problem. You're right. No power to those wires, means no power to the glow plugs, means no start by normal means. Somewhere, between the relay and the glow plugs, you have a bad connection or a broken wire(s). A common place to have a connection issue with the glow plug wires is in the main engine wiring harness plug that's on the passenger's side fender, right in front of the HVAC box. You'll see a relatively large bundle of wires coming over the passenger's side valve cover and going toward the fender. There's a plug in that bundle and that's the one I'm talking about. Look at it carefully. You'll see two larger wires. Those are your glow plug wires. You may also see the plastic covering looking discolored or even melted. If it is, then you have a bad connection right there. Dirt or other crud has a habit of getting inside there and causing extra resistance in your glow plug wiring. If you aren't sure, do an ohms test between the two wires on each side of the plug. There shouldn't be very much resistance. If you do have high resistance, then the easy way to take care of this issue is to remove the wires from the plug and splice them together. Then your glow plugs should start working again.
