Skin ulcers (i.e. deep sores that slowly or never heal) can reek for at least two reasons. First, they may be infected with a bacteria that gives off foul smelling gas (as a waste product of its metabolism). Or, second, they may stink because they contain dead tissue (as for example may occur if the ulcer has formed because of poor circulation).
“Feculent blood” is not a term I’ve ever heard used, nor does it describe any common symptom, syndrome, or complication of which I’m aware. The key word is “feculent”. It does not mean composed of feces, even though it smells as if it is. Rather, “feculent” usually is describing a situation where bacteria normally found in the large intestine (colon) have “overgrown” another, usually sterile, area. The stomach is a classic place for it to occur and when it does, it usually is a reflection of extreme sluggishness, if not outright paralysis, of stomach movement (gastric peristalsis). In other words, a key defense against bacteria taking up residence in the stomach is its ceaseless digestive movement (peristalsis). In the absence of such movement, bacteria don’t get pumped out. If bacteria do overgrow the stomach, and if they are so-called anaerobes normally found in the colon, they have the ability to make the stomach contents smell (and even look) like shit (literally and figuratively).
The above is similar, but not identical to, the situation where the stomach is not emptying, or empties very slowly only after many hours or even days. When that occurs, the food sitting in the stomach begins to rot. Hence the aroma. Rotten eggs is a typical term used to describe it, but not usually feculent.
There are a number of diseases associated with such a lack of stomach emptying, the proper term for which is, btw, gastroparesis. Common causes of gastroparesis include diabetic nerve damage and surgery for ulcers (where the vagus nerve is deliberately cut - not only does the vagus control gastric motility, it also sends the signal for acid release).