I use a multimeter. Without even removing the gp I can see if it's good or not. A good gp should give about 1.4-1.6 ohms. A bad gp that is ~15 ohms will still get hot, but not that fast and not so hot.

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1992 Mercedes 190D 2.5 turbo 5sp manual. EGT+boost gauges. Boost controller set to ~14.5 psi. 1 1/4 turns on full load adjustment. LPG injection. Next in the list is water injection.