I have 3 Tier3 Mazda units (Impco), all converted to CNG.
2 of them have started missing and popping out the intakes. (after ~2200 hours)
No codes, other than the usual STFT <>20%.
Everything checks out with the lap-top, and the miss seems to get better after I reset LTFT's. But only for a while...

I've modded the Tier2's (asin system) to the point that they work well, but they all needed head-rebuilds from running lean for so long.

I was wondering if anyone else was having issues on LPG, just in case this is a self-induced, CNG caused, problem.

The Impco-emissions might be getting damaged from constantly having to be 20-30% richer with CNG (kind of like when the 4.3's were stripping throttle gears)