1996 ford windstar 3.8 codes say that cylinders 4 and 6 are misfiring,system too lean bank 1,egr flow insufficient. whats up?

bank 1 sensor 1 lean code. Check vacuum lines first. Could be egr leak also. Most vacuum lines run on the back side of the engine on these. Most common fail is the PCV 90 degree elbow. On the passenger side.

P0171 System Too Lean (Bank 1)
P0174 System Too Lean (Bank 2)
P0301 Cylinder #1 Misfire Detected
P0302 Cylinder #2 Misfire Detected
P0304 Cylinder #4 Misfire Detected
P0306 Cylinder #6 Misfire Detected

The PO401 you can Google
It is an EGR Issue
The fuel trim could be vacuum leaks,oxygen sensor
issue,cylinder ignition misfires.
Once you resolve the Egr System problem, you continue on
with your testing. Insufficient flow means you have less exhaust
gas re-entering the intake, than you should have,so I would say
you have two or more issues

You have big problems here, I suggest you go to the provided links and read about these fault codes and then hire a good technician.
Ford P0171 P0174 Lean Codes

P0172 OBD II Trouble Code System Too Rich Bank 1 YourMechanic Advice

https://www.obd-codes.com/p0175


P0304 OBD II Trouble Code Cylinder 4 Misfire Detected YourMechanic Advice

Hi, a Ford P0171 is a LEAN code for cylinder bank 1, and P0174 is a LEAN code for cylinder bank 2. These codes commonly occur on many Ford vehicles, and are set when the powertrain control module (PCM) sees the air/fuel mixture is running too lean (too much air, not enough fuel).
When the Check Engine Light comes on, either one of these codes, or both, may be found when a code reader or scan tool is plugged into the vehicle diagnostic connector. IF the vehicle is driven long enough, typically both codes will be set.
A P0171 lean code for bank 1 is the cylinder bank on the RIGHT (passenger) side of the engine on Ford vehicles with a V6 or V8 engine and rear-wheel drive.


A lean fuel condition may exist if the engine is sucking in too much air and/or the fuel system is not delivering enough fuel. If bad enough, a lean fuel condition may cause lean misfire, a rough idle, hesitation or stumble when accelerating, and/or poor engine performance.
Unmetered air can enter the engine through a vacuum leak, a dirty airflow sensor that is not reading airflow accurately, an EGR valve is not closing and is leaking exhaust into the intake manifold, an EGR valve that is allowing too much flow (because the EGR differential pressure sensor that monitors EGR flow is faulty and is under-reporting EGR flow).
If the problem is not enough fuel, the underling cause may be a weak fuel pump, restricted fuel filter, leaky fuel pressure regulator or dirty fuel injectors.

A P0174 lean code for bank 2 is the cylinder bank on the LEFT (driver) side of the engine on Ford vehicles with a transverse-mounted V6 engine and front-wheel drive. This code is not set on four cylinder engines (no bank 2).
WHAT A LEAN CODE MEANS
A lean fuel condition may exist if the engine is sucking in too much air and/or the fuel system is not delivering enough fuel. If bad enough, a lean fuel condition may cause lean misfire, a rough idle, hesitation or stumble when accelerating, and/or poor engine performance . Unmetered air can enter the engine through a vacuum leak, a dirty airflow sensor that is not reading airflow accurately, an EGR valve is not closing and is leaking exhaust into the intake manifold, an EGR valve that is allowing too much flow (because the EGR differential pressure sensor that monitors EGR flow is faulty and is under-reporting EGR flow).
If the problem is not enough fuel, the underling cause may be a weak fuel pump, restricted fuel filter, leaky fuel pressure regulator or dirty fuel injectors.

P0171------ system too lean bank#1
Po174------ system too lean bank#2
For these 2 codes, try cleaning the maf sensor (mass air flow), that is mounted in the big black hose that goes from the air filter housing to the throttle plate, if it is dirty, that will cause those 02 sensors to send a signal to the computor to lean the air fuel mixture. If cleaning it doesn't work, the sensors will probably need changing.
P0300---- Random/multiple cylinder misfire
P0316---- Cylinder misfire at start up---- first 100 revolutions.
On those 2 codes, you have to do some testing to find out why there is a misfire.
Possible causes:
dirty/malfunctioning injectors
weak coil pack
fowling spark plugs/wires
Low fuel pressure

#1 is the egr position sensor #4 Is for single cylinder misfire so this could be the coil or a bad plug or wire ..but with fords should check for a vacume leak that can cause a misfire to .....#2#3 are 02 sensors before i would change them i would check the mass air flow sensor ..Hope this helps

i had asimiliar misfire on my 2000 windstar.the first thing to check is a broken valve spring by taking off the valve cover the other is a o2 sensor bank 2 i believe is the downstream.if not the valve spring then either the coil pack or thecontrol module. either way it is fairly inexspensive

Bank one is toward the front of the vehicle. Sounds like the heated oxygen sensors have gone bad. The Oxygen Sensors are located in the exhaust pipe and require a special socket to remove and replace.