The kit has a thick hollow cylinder you are supposed to install around the injector fitting to displace the volume the same as the M-B injectors. I don't know how close it matches, but I measured ~405 psig on most cylinders of the replacement engine for my 1985. The original engine measured ~250 psig and didn't like to start on cold days (later failed). Thus, I doubt it reads low and is certainly useful for diagnostics.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans