I have a 96 Nissan xe, I've changed plugs wires, distributer cap, fuel filter and 1 fuel injector. It still runs really bad and the exhaust has a very strong fuel smell

have the fault codes read . there are a few sensors that control the starting of the car including the engine immobiliser.

Check for compression on your cylinders. That would tell you if you have a bad head gasket or a bad head.check your distributer and see if is good, i seen that happend too

check fuel filter,or fuel injectors, fuel pressure regulator.Also check fuel filler cap.Check exhaust system for plugged catalytic converter,muffler,bent exhaust pipes,etc.

Lots of early Nissans had a fuel feed pipe problem The plastick pipe split causing fuel starving engine missing

DETERMIN IF YOUR PROBLEM IS ONE OF THE FOLLOWING BEFORE CHANGING ANYTHING .1.ELECTRICAL
2.FUEL RELATED OR 3. MECHANICAL.

PERORM A COMPRESSION CHECK TO ENSURE THE COMPRESSION IS GOOD .IF THE COMPRESSION IS IN ALL CYLINDERS PROCEED TO CHECK FUEL SYSTEM .REMOVE THE FUEL INJECTORS AND EXAMIN THE INJECTOR TIP FOR CARBON DEPSITS .CHECH FUEL SPRAY PATTERN ,ENSURE INJECTORS ARE ACTUALLY SPRAYING . THEN PROCEED TO EXAMIN THA SPARK PLUGS .LOOK FOR DISCOLOURATION OF SPARK PLUG ELECTRODES OR CARBON DEPOSITS. IN DIAGNOSING PROBLEMS ONE HAS TO SYSTEMATIC OR ELSE YOU WOULD BE WASTING MONEY AND TIME PURCHASING AND REPLACING COMPONENTS WHICH ARE NOT DEFECTIVE . GOOD LUCK .

You've already eliminated the spark plug & wireset, distributor cap & rotor.
Sounds like your car needs a tune-up, specifically, the PCV (positive crankcase ventilation) valve, and/of the EGR (Exhaust Gas Recirculation) valve.

Components checked/replaced during a tune-up are:
air filter
motor oil
motor oil filter
breather filter
fuel filter(s)
fuel strainer
PCV valve
EGR valve
spark plugs
spark plug wires
ECM or distributor cap & rotor
cabin air filter
transmission oil filter
transmission oil
engine coolant
check all vacuum hoses and lines

Troubleshooting the no-start condition - from the 1990 Mitsu Mighty Max Repair Manual:

Priority Action Part Type -- Cause
1 Inspect Battery -- Battery Discharged or Faulty.
2 Inspect Battery Cable -- Corroded, Broken, Shorted or Poorly Connected Battery Cable.
3 Inspect Distributor Cap -- Distributor Cap Cracked or Burned.
3 Inspect Fuel Filter -- Clogged or Dirty Fuel Filter.
5 Inspect Ignition Coil -- Faulty Ignition Coil.
6 Inspect Wireset -- Worn, Damaged or Faulty Spark Plug Wire(s).
7 Inspect Spark Plug -- Incorrectly Gapped or Fouled Spark Plug(s).
8 Inspect Starter -- Starter Motor Faulty.
9 Inspect Fuel Pump -- Low Fuel Pressure.
10 Inspect Solenoid Switch -- Faulty Starter Solenoid Switch.
11 Inspect Fuel Pump Relay -- Faulty Fuel Pump Relay.
12 Inspect Fuel Injector Pressure Regulator -- Faulty Fuel Injector Pressure Regulator.
13 Inspect Ignition Switch -- Improperly Connected or Faulty Ignition Switch.
14 Inspect Starter Drive -- Faulty Starter Drive.
15 Inspect Fuel Injector -- Dirty or Worn Fuel Injectors.
16 Inspect Fuel Pump Strainer -- Clogged or Dirty Fuel Pump Strainerat.
17 Inspect Engine Control Computer -- Incorrect Operating Information Being Delivered and Sent From The EEC.
18 Inspect Fuel Tank -- Fuel Tank Empty.
19 Inspect Carburetor -- Carburetor Flooded or Faulty Choke.
20 Inspect Distributor -- Worn, Loose, or Incorrectly Installed Distributor.

Thats where I would go next. You can check the converter by removing the 02 sensor in front of it. If the engine runs better, then the converter is clogged. Also if the exhaust that comes out the tail pipe is very very hot it's the converter.

Change the lambda/oxygen sensor in the exhaust.

Check the injectors. They are really bad about leaking on the 4.3's.

HAVE YOUR EXHAUST CONVERTER CHECKED! IF IT'S BAD AND YOU HAVE IT REPLACED, DON'T LET THE ONE THAT REPLACE'S IT TAKE YOUR OLD ONE!!!!! IT'S WORTH ABOUT $250.00