Based upon my research, the CSFI systems used in GM's Vortec engines during the mid to later 90's are problematic. As such, it does not appear uncommon to convert these to MPFI system.
I have a 96 Chevy Express/G10 van with a 5.0 CSFI. Currently, the van idles rough, sometimes has a strong exhaust odor, makes a "pinging" noise occasionally (mostly around 30 - 40mph, light acceleration or deceleration), surges/misses primarily during deceleration when cold, and occasionally hesitates under heavy load. My initial impression was a vacuum leak (seems like it is running lean). I have spent significant time and money in attempting to diagnose this issue. The "Check Engine" light is not on. I have cleaned the throttle body, EGR valve, replaced plugs, wires, distributor cap and rotor, and changed the fuel and air filters. I have recently had an leak at the right exhaust flange, and no one seems to be able to find a vacuum leak. The readings on my vacuum gauge looked good. While I have not tested it personally, a shop tested the fuel pressure levels and said they were acceptable.
As such, I am starting to wonder if the injection system could be the culprit. To clarify, I am curious is the symptoms outlined above could be caused by problems with the poppets and, is it possible that such a problem would not throw a misfire (or other) code? Is there any accurate way to determine whether or not the CSFI system is in need of replacement? It is quite an expensive endeavor, not something I want to try on a whim.