Ah makes sense now, thanks! I will hook the truck up to a scan tool sometime during the weekend if I get the chance. I will probably just replace the vacuum switch as a new one is $15, which is way easier than testing XD once I run the tank down a little more, I will update mileage readings.

 

The diagram is not exactly how it is on the vehicle. It's just easier to show how they are routed. There is a vacuum check valve, a vacuum reservoir, vacuum tees in the source etc etc that are not shown. The transfer case vent tube is steel and it's above the vacuum switch. It sticks out about an inch and makes a 90 degree turn rearward, then changes to rubber, (you can see the yellow hose clamp) and continues to the dipstick tube where the filter is located.

 

heck i think thats what the end of the hose looks like

 

Hard to tell for sure, but that sure looks like it!

 

makes me wonder why its taken off......

 

Maybe got caught on something while driving and pulled it off.

 

youd think it goes over the tcast, or between the tcase and skidplate to protect it.

 

Changed out the vacuum switch. Noticed what might be a slight decrease in fuel consumption, but wont know for sure until next fillup. Also noticed a dent in my fuel filter so I changed that again and my slight hard start is gone on cold mornings. If things are better, that would be great, but I still seem to be noticing an abnormally fast drop in my fuel gauge. The only things I can think of left would be a mass air, ECT, upstreams and fuel pump. 3 of which are more than just a $30 fix. Really hoping it's not the pump. Not when it's this cold

 

Re-ran a fuel bleed down test and the numbers were better today. Only had a Mercedes factory bar gauge so I will posting both numbers:
KO/EO reading was 4.2bar or 60.9PSI (bar x 14.5)
After 15 minutes reading was 3.8bar or 55.1PSI, which puts everything within spec. No more hard starts after sitting. Mileage seems to have improved slightly. Still haven't been able to hook up to the MDI to check sensors and fuel trim yet. When I am not swamped with everything else that is going on, I will hook her up and post all the different readings I get. Noticed today that my left rear tire was a 28 PSI, whereas the rest were 34-35. I filled them last week to 35, so I have a slight leak that I need to address. Still noticing an intermittent front end hop on tight turns. That is starting to bother me and I can't seem to figure out why it's doing it and why so inconsistently. Going to pull the plugs either tonight or tomorrow night to see how they look. They are less than a month old so any fouling would be a bad sign. Would the coil be starting to go at 136K on these things? Of all that I've owned, I have never replaced a single coil, so don't know if it could be going bad, killing my spark energy.

 

Both fuel pressure and leakdown are at the bottom of the allowable spec, so no room for error there. This could also mean fuel volume is at the low end as well. Might be worth checking maximum output pressure at the filter. Should be 73psi to 108psi. With these coils, they usually "leak" to ground from the tower. Not a real common issue, but it does happen.