Just thought i would post me results. New ferret adapter and digital light with tach /advance showed up. My timing by ear, which i thought was a little advanced due to the bottom end knock if you lugged it, turned out to be 11.7* BTDC Have it at 8.4* BTDC now, will see what / if that changes and go from there. Does seem to start better.

On another note, i notice that, litterally the instant i touch the throttle, timing goes from around 10* at idle 730 rpm to 8* by 800 rpm, and doesnt move at all from there to redline until you let completely off again. Perhaps the reason why it seemed to run better the more i advanced it, but we will see.

 

Just remember how the timing on these engines works.
You have a couple of factors happening here:
1. As engine speed increases, any given timing point becomes more retarded due to the fuel taking the same amount of time to burn.
2. As you add more fuel(richer mixture) due to load, the timing will be more advanced due to a hotter burn.
3. As you add more fuel, due to the plunger design of the IP, it changes the injection start time to be earlier. Effectively advancing the timing slightly.
4. As RPM increases, the IP's internal transfer pump(vane pump) creates a higher pressure, which is applied to one side of the "timing advance piston"
5. As throttle position increases, the "light load advance" cam pushes in a piston which pushes against a spring; this spring is on the opposite side of the advance piston. This retards the timing.
6. The timing advance piston's "free" side has housing(return) pressure acting against it. The cold advance solenoid drops the housing pressure from ~5 PSI to 0, which reduces the retarding force against the advance piston, effectively advancing it.

Does this sound complicated? It is. There are lots of factors involved with timing, and it's not just a linear curve here - it depends on RPM, load, housing pressure and throttle position.
Any of these elements changes(like the advance piston wearing, creating less advance force due to pressure leaking around it) and you'll change the entire curve.

This is why, with a /new/ IP, you can easily time it and things will be good.
With a worn one? It's a matter of adjusting it so the timing is 'right' over as much of the curve as you can, fudging with the light-load advance cam to change where it pulls timing, and hoping for the best.


Honestly, now that you can play with the timing and have some reference point as to where you are, you might want to try doing things like:
1. Advancing the overall timing until it handles well in the mid to upper range.
2. Rotating the light load advance cam to advance or retard the idle and low end timing; try to find a medium point where you've got good response throughout the range.

 

also fuel supply pressure to ip will change the timing, and the reactions of fuel curve, pressure and volume are different, and you may be surprised, buy what you find...

 

I have a steady 5lb fuel supply. I advanced it to where it seemed to run best most of the time (11.7), however, that killed off idle power, made it a little cranky to start when its hot, and would pre-detonate if lugged below 1500ish rpms. I was doing all the previous timing adjustments by seat of the pants. Now that i have a light, ill compare fuel mileage, and ill keep an eye on egts to see if there is a difference, same for power. This pump i have swapped on there, has some atypical settings compared to my other pumps. Its dark, or id go look, but on most pumps "this" is about "there" "that" is about "here", of the four i have, 3 are identical to the eye, the one that is on there now however, is all sorts of out of whack. In fact, i had to advance the gear a tooth just to get the thing to where it is now (8.4*) and mind you, the marks are damn near aligned. I put this one on, thinking it was the better pump, the engine it came off of ran just awesome, i swapped it with the injectors from said engine. Im less impressed with it in my 92. Some other things, now that im off topic. The 88 that the pump and injectors came off of had a very loud rattle at idle, and great throttle response. However, on my 92 its the same quiet idle (even at 12* apparently) and mushy response, and was capable of 17mpg with a C6. The 92 has never gotten over 15, and is currently getting 14 (another reason for swapping the pumps) Starting to suspect something off the wall, like plugged return line or something.

If i get bored and have the time, ill do a compression test. Cant on the 88 unfortunately, but when i tore it down, it looks mint inside, minimal wear, granted, it was a lower mileage engine.

 

Y'know, it's kind of funny. My tan 88's always been pretty loud and clattery. It just is. It'll quiet down under load, and I can eliminate the diesel clatter by retarding it a lot... but it's just plain loud. It always vibrates a bit, before and after I had it rebuilt.
My other blue 88, on the other hand... it's quieter. Sure, still an IDI, still sounds IDI-ish, but it's definitely quieter overall.
Why? I have no clue. They both are basically the same truck(4x4, zf5, 7.3 idi, extended(tan) vs single(blue) cab, turbo(tan), NA(blue)).
Oh, and my dad's red 88(single cab, turbo) sounds distinctly quieter overall, even when it clatters. It's just a different tone.

And I'll point out that I've had four different pumps on my tan 88 - from the original which had a screwy hydraulic advance(you could time it for either "works nicely at the low end, barely revs above 2,000 and clatters" or "runs nicely above 2,000, has no power at idle), to a more normal junkyard pump, to a 6.9 rebuilt craigslist pump, to my current RD2-110 pump... and they all do basically the same thing once I get the timing where it needs to be.