I have a 1987 z31 I am getting a random misfire and spudder mostly after warm up or longer drives it mainly happens under pressure or at high rpms computer pulls no codes and no one can seem to tell me the correct problem it dose have black smoke on occasion as well
I've already put new and check
Distributor cap , rotor ,plugs , wires , water pump , CHTS as known as coolant temp sensor, all my injectors have been tested , new fuel filter , and fuel pump has been tested , timeing seems to be on point . also good compression on all cylinders

 

if all you did did not cure the problem you have a real puzzler. particularly because it is random. could be a loose or corroded connection. following is some stuff that may or may not help this particular issue but will definitely help stave off other weird things in the future. :
Get your battery load tested. Be sure you have clean, tight corrosion free terminals on both ends of your battery cables. Be sure the ground (negative) cable goes to a bolt into the frame before going to the starter. grounding through the starter is not a reliable connection. Z's don't like low voltage. causes the electronics to act funny. it is possible to have enough amps to crank but not enough voltage to run the electronics. If you have one size fit all cheapo clamp on terminals they are a problem waiting to happen. Usually on a rainy night around Oh Dark Thirty.

Clean the connectors for the maf or afm, ecu and tps. Deoxit by CAIG is probably the best connector cleaner on the market. spray with CorrosionX after cleaning and before putting together this will help prevent any further corrosion. DON'T USE DIELECTRIC GREASE.

is your battery strapped down or just bouncing around in the battery tray.

 

Try unplugging the AFM and see if it clears up, when mine acted up caused all kinds of wacky behavior.

 

where in the US are you ?
one weak link associated with mass meters is high humidity
the nichrome wire in the meter runs at 900 degrees air flowing ( goes to 1700 for a split second to clean it ) over it cools it to increase the settings to the FI , the more air, the cooler the wire
now through in some moisture and it goes way rich . We used to get a lot of surging problems in very wet conditions @ Nissan , with no fix according to the factory service reps
it also effects connections