400 is good, when I did mine I would have left it alone if it would have just stayed above 300, mine went from 300-200 from 1-8. I “borrowed” a gauge and adapter from a local diesel shop (they charged me like $25 to borrow it for a couple hours). Just remove all glow plugs and then test each cylinder. You need to watch the gauge as the engine turns and pay attention to how much the needle bounces on each compression stroke. Better have a battery charger hooked up.
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