Nissan Repair: 94 altima, crankshaft position sensor, air flow meter

Question
Ok I bought a 94 altima for my son. Ran great 1st day then starting acting up. Car starting running rough. maf sensor connector messed up. car would not run over 2500 rpm. Replaced ran better. But started smoking black fuel smoke.replaced fuel filter,tps sensor still same, then o2. sensor still same. Dumping to much fuel still. Replaced fuel reg valve. Guess what still same. I kept looking at your posts. I took your advice and replaced the Dist,the cap,rotor button. lucky for me have a friend at the parts store.Still same black smoke runs rough. ecm code 1 long 2 short. maf circuit. checked voltage on lg orange wire on maf connector 12.37 v plugged back in to maf checked sm orange wire with meter read like 7.50 volts. could ecm be completely cooked ??????? all plugs have carbon completely covering them ?????????

Answer
Joe,

Sounds like the new MAF is defective since you have the codes to support that diagnosis.  I would try another MAF before replacement of the computer.  Also, be sure the connection is clean and secure at the MAF as well as the harness that feeds it.  I have seen cars that have been in a wreck with a damaged harness to the MAF and under tape it gets missed.  So, check the harness really good to make sure it has not been cut or spliced back together poorly.  Here are the codes and how to read.  

Diagnostic Trouble Codes - 1987
Nissan
11     Crankshaft Position Sensor
12     Air Flow Meter
13     Cylinder Head Temperature Sensor
21     Ignition Signal
22     Fuel Pump
23     Throttle Valve Switch
31     Load Signal
32     Start Signal
41     Fuel Temperature Sensor
44     System Okay
1.   Verify that diagnostic mode slesctor is turned fully counterclockwise.
2.   Turn ignition switch ON.
3.   Make sure inspection lamps stay on. (Bulb check.)
4.   Ture diagnostic mode selector fully clockwise.
5.   Make sure inspection lamps display code 23 and 31.
6.   Depress accelerator pedal and release.
7.   Make sure inspection lamps display code 31.
8.   Start engine, apply brakes and shift into "D" position.
9.   Make sure inspection lamps display code 31.
10.   Turn a load switch OFF-ON-OFF. (A/C switch, Headlight switch etc.)
11.   Shift into "P".
12.   Make sure inspection lamps display code 44. Any other code is a DTC.