GM-GMC: engine miss, gmc safari, obd ii

Question
I have a 1999 GMC Safari Cargo Van.  When I run the AC the engine picks up a miss and loss of power.  It has done this since it was new.  I took it to the dealer.  But they could find nothing wrong.  It runs great as long as I don't use the AC.

Answer
A loss of power when using A/C can vary between vehicles and is determined by engine size, gearing, and load carried.  Some vehicles are more sensitive than others.

The miss is not normal.  It is likely ignition-related and the spark plugs, spark plug wires, and distributor cap and rotor (if used) should be checked or replaced.

The vehicle has OBD-II diagnostic capability and should be checked for stored trouble codes.  Many auto parts stores will read the codes for free.