I bet the canister is leaking thru a weephole (mine did), here are some picts of the canister and you can see where is in front and behind the housing.
click to enlarge.
and the older canisters (before ´96) looks like this:


you also can use this for detect the leak:
http://spectroline.com/hvacr/hvac_dyes_gasglo32.html

I hope this helps you.

 

Found out what it is called on the back of the fuel filter housing below the fuel line on my 95 PSD. Vacuum Switch, $52 from ford, took about 5 minutes to replace. Now if anyone knows what it is for Ill buy them a cookie, the guys at Ford didnt even know. Part # e8tz-9s283-a

 

thats the fuel filter restriction switch that I was talking about. LOL I like double chocolate chip!

 

As usual,, good post .....

 

............................. (thanks for that)

 

where are the weep holes?

 

In reallity only the fuel pump has a wheep hole, the canister because the slugde in the botton becomes to be roted or eroded and a tinny wheep holes are formed IMHO.

 

Not viable??? I was thinking of maybe suggesting to remove the fule filter cover and adding black dye maybe food coloring to the fule. Sounds like a good idea to help find a leak. Around here the diesel is clear so finding a leak can be a pain.

 

Just take off your fuel filter cover, take a couple cans of carb clean, get your valley cleaned out as best you can, then blow it out with some air. Once it's all clean start your truck, get up over the engine and as you will notice there are a few different sumps in your valley, there are 2 right around the fuel pump area, if the pump is leaking out the weep hole it will begin to fill up the sump 2nd from the back of the engine, there are also 3 lines from the fuel pump to the filter to watch to. Also keep an eye on your filter housing, there is the sensor on top and also the water/fuel sensor on bottom, they are both leakers. Most of the the time since the fuel change to low sulfer we've been changing fuel pumps more often then the sensors (never the cheap fix). The weep hole I'm talking about is actually on the fuel pump itself, once you pull it out of there you will see it. This can be done easily enough without removing the turbo to, the only tricky parts is getting that banjo fitting started agian.