1993 F-350 460 E4OD

The scan tool show the HO2S holding a consistent .9 volt while running hot after starting at .04 volt when cold. To verify this I made a test harness to attach a multimeter. The multimeter gave the same results. To make sure that the PCM wasn't messed up I used the connectors on the test harness to disconnect the HO2S from the PCM and got the same results. The scan tool shows open loop even when the engine is at operating temperature.

Now I need to find out if the HO2S is faulty or if the exhaust is truly too rich. The HO2S has about 300 miles on it.

How do I tell if the HO2S is working right? What would it read when removed from the exhaust pipe and the heater on?

If the HO2S is giving accurate results, what is causing the engine to run rich?

 

Open loop = always rich. My 96' holds steady at 0.9V on both banks in open loop. Closed loop is when you see the sinusoidal switching between rich/lean/rich/lean.

Why is it not going into closed loop would be what I focus on.

 

Do you have any O2 codes? Boarding has it right you need to be in closed loop to see the accurate PID of the O2, It may not go in to closed loop because of the rich exhaust, force a vacuum leak on that bank. Disconnect a vacuum line and see if it goes lean. I always test O2's in the truck as they only produce voltage at a certain temp, and you can OHM out the heater part of the O2 if it reads Infinity you have an open in the heater circuit, they added the heater to them so the truck will go into closed loop faster than the old single wire O2's back in the day!! You said 300 miles?? It's new?? Is anything contaminating it? Damage/corrosion to the connector or harness?? Make sure the fuse for the O2 heater circuit is OK, though they don't have separate fuses anymore, it is probably on the PCM or something else! Good luck

 

No HO2S codes except after KOER test when the code given is O2 sensor higher or lower than expected. After clearing this there is no code set from driving. There is resistance and voltage at the connector. The resistance goes up and current goes down when heated as would be expected from a PTC heater, so the heater is good.

Yes it is new. There is black soot on the sensor as would be expected from running rich. During the bench test the voltage only rose a slightly in open air as the heater got hot. I don't know what it should be but since it compares the exhaust to ambient it is probably right. Applying and removing the flame from a propane torch caused the voltage to range from near zero to .9 very quickly. This means that it is good, right?

What I can see of the connectors and wires, all look fine.

The way I understand it is that it will stay in open loop until the sensor voltage out passes .45 volts. This tells the computer that the sensor is hot enough to work. It will then vary the fuel delivery to try to maintain .45 volt.

As Boarding said I need to find out why it is not going into closed loop. What could cause this? The PCM? Other sensors? I really don't know where to start. I can't afford to start throwing parts at it. The inside of the ECM has good solder joints and dry capacitors.

I tried to find out if I have the right PCM installed but had no luck. The Calibration number is 3-98A-ROO. The ECM is E9AF 14A624 AA. Are these a good match?

Thanks, guys