I have a 97 Ford Explorer AWD 8 cylinder. Check engine light comes on and I get code p303. Vehicle bucks at times, uses lots of gas. Believe it may be 02 censor, spark plugs and wires tested ok. Any Idea

cylinder 8 is missing combustion which caused the o2 code the black box will not cause a specific cylinder to miss, there fore a fuel distribution problem is evident, the injector on eight is proablly the culprit the #8 cylinder is the last cylinder to be fed a fuel, pressure test is needed to determine if the fuel pump is strong enough to deliver diesel, ambulance spend a lot of time idling causing fatigued fuel pumps

what engine if a zetec engine then change the O2 sensor

When standing in the front of the vehicle the cylinders are numbered 1-4 up the passenger's side and 5-8 up the driver's side.

Firing order for the 5.0 liter V8 is

• 1-3-7-2-6-5-4-8

stop by local parts store (Autozone,Advance, etc) and have them do a free fault code test. They can print out a list of faults and clear the codes

Good Evening, I don't remember seeing a p9303 code, but a p303 is a misfire code on cylinder 3, I would tell you to double check your plug wires and definitely make sure #3 is sparking. Also be sure to check the spark plug gap since you just put it in that it is possibly a little off. Hope this helps.

might have a bad o2 sensor wich is tripping your check engine light and a vacuum leak wich is causing your 4lo 4 high light to blink

Your vehicle is OBD2 compliant and you will need a scanner to access the code. Some auto parts stores will access the code for you free of charge.

check firing order that you put the wires on right then 1 at a time pluck the wires off and replace them when you do this each one it will make the motor shake a bit more, keep checking till you pluck on the wire that shows no change in the running condition and check that wire and plug to see witch one is bad

HOPE IT'S NOT PISTON SLAP, IF LACK OF MAINTANENCE WAS THE CASE MAY BE INTERNAL DAMAGE OR VALVETRAIN DAMAGE. IF IT RUNS ROUGH MAYBE SOMETHING ON ROTATING ASSY DAMAGED.

Looked up your OBD II code for your Explorer and got the following: Bank 1 Sensor 1
The possible causes are listed below per Chilton: *same result for all engines available on your vehicle

Trouble Code: P0141 (4.0L V6 VIN E Auto)
HO2S-11 Heater Circuit (Bank 1, Sensor 1) Print this code data
Number of Trips to Set Code: 2
OBD II Monitor Type: CCM Details
Indicators: MIL Details
Trouble Code Conditions:
During testing the heated oxygen sensor (HO2S) heaters are checked for open and short circuits and excessive current draw. The test fails when the current draw exceeds a calibrated limit or an open or short circuit is detected.
Possible Causes:

• Vacuum hose disconnected on exhaust gas recirculation (EGR) system module (ESM) applications* Short to VPWR in the harness or HO2S
  
• Water in the harness connector
  
• Open VPWR circuit
  
• Open GND circuit
  
• Low battery voltage
  
• Corrosion or incorrec
  

The sensors themselves appear in the illustration linked to below. The illustration is for the Ford Ranger but indications are that other models have similar locations. Hope this helps with your problem. Best of luck!
Greg

http://www.chiltonlibrary.com/content/images/8968/images/89684g23.pdf