So far, the only actual evidence I have is carbon deposition on 25 year old injectors. Until today.
To prepare to replace the injector pump, I had the doghouse off of the engine to survey the work. Aside from the need to remove the left front fender liner to get to the injectors on that side, the forward control step van chassis makes it fairly easy to work on the engine. And, the L57 normally aspirated engine layout makes the job mostly accessible right from the cab. My biggest concern is rigging a shield to prevent dropping the three driven gear bolts.
While I was surveying the work, I had the air cleaner off, exposing the fuel filter manager. Since I keep a spare filter, I thought it might be foolish to begin the job to replace the injector pump before having a look at that fuel filter.
The amount of brown crud in the bottom of the fuel filter manager was shocking. I don't know the age of that buildup, but the filter was visibly loaded with it. It took me quite some time to clean it all out of the fuel filter manager, before installing the new Wix 33976 filter, and taking it for a test drive. What appears to be a place to attach a piece of hosing to bleed the filter, is nothing but a knob to nowhere. The Wix filter bleed just leaks fuel out all over the top of the filter cap when the air is gone. You want a rag to catch that fuel.
I suspect flow through that heavily clogged fuel filter was pretty restricted.
The smoking was really getting heavy sometimes, to the point where I was avoiding some roads with speed limits that caused it to smoke. It was visibly smoking in normal driving conditions, now. Why the rapid onset? What can change so dramatically, so quickly?
I think the answer is it was me.
With a fresh fuel filter, the stumbling starts that were increasing stopped. The smoke on start stopped. I took it for a test ride and had difficulty making it smoke. Though, the engine had returned to the light, occasional smoking that I described in my first post. Until I let loose a couple cans of Seafoam into my fuel tank. I think I clogged my fuel filter.
I think that Seafoam did what it says it will do, and flushed all sorts of crap from the fuel tank, crap that had been there for 25 years, and was now clogging my fuel filter.
I'll replace the fuel filter again in a week, and we'll see what needs to happen next. I have to have a perfect fuel system before I go for that injection pump.
On the ride back from our test ride, I seemed to lose a cylinder, with a loss of power, rough running, and a hell of a clatter from that cylinder. It smoothed out while I was seeking a safe place to pull over, and returned to running normally. As if an injector were momentarily blocked.
The crud in the fuel filter manager and the visibly clogged filter are solid evidence, and I think could cause fuel starvation. I wonder if what I felt and thought were power bumps were actually dropouts from fuel starvation. I don't know exactly what that feels like or sounds like, either.
Finally, the tone of the engine has returned to how I remember it sounding, particularly on startup. Before replacing the fuel filter, it had a much sharper diesel clatter, noticeably quieter again now.