The "War & Peace" edition of troubleshooting this problem:
About 20k miles/450 eng hrs ago, I spent a Saturday making the following changes under the hood of my '96: I put in a set of Red Oak injectors, installed a #8 torque plate and slid it forward about . 049” from stock, slid the AFC housing full back, disabled the factory turbo's wastegate by replacing the actuator's sensing line elbow fitting with plug in the compressor outlet, confirmed timing still at 15. 5° (per plunger lift method). I also set the high idle adjustment screw on the P7100 up to 3600 (had to then also make a significant throttle linkage adjustment to get the accelerator pedal & cruise control to fully open the throttle) - not sure why folks change springs when there appears to be enough travel in this adjustment to successfully blow the engine.
After my first test drive, I moved the AFC housing back forward about 1/3 of the distance moved previously to cut back on the thick black smoke when flooring it off idle. This resulted in a brief puff of black smoke that quickly cleared up as the boost climbed past 5psi.
Engine started and ran good then and still does. Also unchanged from then to now is flooring it quickly brings boost to 34. 5psi on the factory turbo (sucking the filter minder down to 16" H2O across a new filter in the process) and pre-turbo EGT to 1225° (both by 1800 RPM) holding steady until I let off the throttle well past posted speed limits. My major goal was reducing distance required to pass on 2-lane road and I am very happy with the results then and now. When not hauling or pulling a load, this truck will easily walk away from the 3800 in the Caravan.
However, I started noticing over the past several months that I got gray smoke when starting cold (even with ambient in the 50°'s) that thinned out as the engine warmed up. If the temp was much below 40° & I didn't have it plugged in, I got quite a blast of gray smoke. There was a heavy diesel odor to it. Even after the engine is warm, there is a light haze of gray smoke at idle-light throttle that goes away as the load/throttle increases. Flooring it, of course, sent out a small blast of black that clears away rather quickly as the engine & turbo spool up. My fuel economy was also down by 1-1. 5 mpg for the same type of driving over identical routes as compared to several fill-ups immediately following the power upgrade. There was no coolant loss and engine oil usage is about a half-gallon every 8000 miles (about what it's been for the last 200,000 miles). Fuel filters are all clean.
I had this issue previously combined with long crank times to start before I did the power upgrade and that time, I found the timing had slipped to about 0°. Correcting that back to 15. 5° and both the hard starting and the cold smoke went away. So when I started noticing grey smoke when starting the engine cold, I checked the timing again and verified that it is still right where I had set it before: 15. 5°.
I still don't have a means of verifying fuel supply pressure into the P7100, but decided to replace the overflow valve in any case and see what happened and my problem appears to have been solved.
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