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The DS IP's can sometimes have some codes indicating failure due to timing or other fault. But usually its best to eliminate all other causes that might make the IP seem bad ie air in fuel, poor supply, bad fuel, or grounds etc. There is no easy way to test a failing PMD/FSD except swap it out with known good one.
DB IP's ???? Depends on the symptoms but again best and usually easlier to eliminate all other possible causes first.
To test the IP itself to specifications like flow and calibration you have to take it off.