Ford Repair: failed emissions, temp gauge, catalytic converters

Question
QUESTION: I have  a 1992 ford van with 351w , hc and co are very high nox is good have replaced o2 sensor and temp sensor and full tune up, get code 173 running rich bank i sensor one what will cause this to burn rich , it is port injected
ANSWER: Hi Toby thanks for asking and sorry about the delay.
The first thing I would do is check the ignition timing. If it is too advanced the emessions will show hight HC na Co  emssions. With the timing too retarded your hc and co go very low but your nox will go down. It will have to be timed untill you are in the position where all 3 gasses are evened out. At the sme time i would check the condition of the catalytic converters. Take temp readings of the cat-- input and output-- the output reading should be about 20-30 degrees hotter with the engine fully warmed up. iF not also replace any catalytic converters.
good luck
Chris P


---------- FOLLOW-UP ----------

QUESTION: HI chris I have checked timming and is ok here my question I had back probed the o2 sensor and watched the ohm readig as it warmed up it would climb to 198 and go back to 0 and start over never getting to 200 to close the loop I had thought it might be the temp sensor seeing that it did reach the half way mark on the gauge as soon as it would hit the o innormal I would feel a hesitation like it was trying to close the loop and the check engine lightr would come on, now if I turn off the truck and restart it the light stays off if i go on the high way the temp gauge reaches the middle of the gauge and the check engine does not come on but it will if I am in the city because the temp gauge drops down to the o  on the gauge (what i mean by that is the o in the normal range of gauge, now what if i would put a resistor in line from the temp sensor so that it would read higher would the computer go to closed loop or am I not on the right path . the only code that comes up is 173 burning rich heated o2 sensor unable to switch how can i get it to stop burning rich and if you think this idea will work what size resistor would you recomend so the truck will still run some what ok untill it warms up  Thanks toby

Answer
HI again Toby, sorry about the delay.
O2 sensors need to be checked with the voltage reading. it should constanly be flucuating between .1-.9 volts. If it is steadly at one voltage then the O2 sensor will have to be replaced. Nox emmisions are due to high combustion temperatures. Try replacing the thermostat, that has been affective for me a few times, double check those O2 sensors. If the light comes on and off like that then there probably is a fault 02 sensor.
good luck
Chris p