Can someone with a d1 4.0 with good cats tell me what voltage readings you see from the after-cat O2 sensors? I am still getting P1313 and P1314 codes and it seemd to occur when the after cat O2 voltage on my Ultragage get up to .3 VS the .25 it ususally runs and often occurs on start up when it is running open loop or when still cool climbing a hill at 20 MPH. The before cat sensors are showing pretty close to a lambda of 1 on both banks.

I gleened this from How to Power Tune Rover V8 Engines for Road & Track By Des Hammill:

The self learning capability of the GEMS 8 system through the clever use of two wide band, heated, 5 volt Lambda sensors insures that all of the engine’s operating requirements are optimized for perfect running under all conditions. The ECU is fed information instantly about air fuel mixture ratios (between 16.5:1 and 11.0:1 – as wide a range as any engine will ever operate under).
There are four electrically heated Lambda Sensors, two before the catalytic converters and two after. The two before the cats relay information to the ECU to control fueling; the two after measure oxygen content after the converters and if it is too much or too little initiate a fault code and light the MIL indicator lamp, but have no effect on fueling. The later type Titania wide band TO17 lambda sensor works opposite to the earlier 1 volt zirconia type. The higher the voltage reading the leaner the AFR and the lower the voltage the richer the mixture; at lambda one (14.7:1 AFR/0.5 CO) the voltage feedback from the sensor is between 2.5 and 3 volts.




Are the after cat sensors also wide band 5 volt units or 1 volt units? should they be seeing a lambda of 1 also or should there be less oxygen after the cats?

 

the two post-cat O2 sensors are the exact same part as the two before the cats. as for the readings, i'm not sure what they should be. but i don't think the should fluctuate very much.

 

They're narrow band zirc. too.

 

I had thought I was reading lambda from the before-cat O2 sensors, because they were running just either side of 1, but I found the UG does not list wide O2 sensors or lambda as a gage choice for the OBDII protocol my Disco is running and is reporting only voltage for all four O2 sensors. The after-cat sensors are running in the 0.0XX region and I have seen the bank 1 before-cat sensor get as low as 0.55 but it usually stays around 0.9X while the bank 2 before-cat sensor stays nearer to 1.0. I've had the MIL start flashing when both after cat sensors were at 0.015, so I don't know if they are triggering the MIL or if it is something else. P1314 is usually the first code set, but having both P1314 and P1313 set is common.

Now I wonder if Des Hammill was incorrect about GEMS 8 using wide band O2 sensors, or if only certain models of Range Rovers used them, or if I have the wrong O2 sensors on my 98 Discovery. I think my ECM says Lucas GEMS 8.3.

Des's book also says, Early “Titania” Lambda units used on Lucas 13CU, 14CU, and 14CUX injection systems had a maximum output of 1 volt with zero to .54 volts indicating a rich mixture and anything over .54 volts a lean mixture meaning that 0.54 volts corresponded to 14.35:1 AFR, the most efficient for a Rover V8. The later “Titania” Lambda Sensors are used on the GEMS 8 engines.


So I am now officially and totally confused about what the O2 sensor voltage readings SHOULD be before and after the cats and I haven't yet found any answers in the RAVE.

 

I ran across this chart shown with a Bosh universal O2 Sensor on Amazon.com at that apparently says any voltage between 0.2 and 0.8 indicates correct air/fuel ratio and above 0.8 is rich and below 0.2 is lean.


My upstream O2 sensors tend to be above 1.0 cold and around 0.9XX to 1.0 when warm. I don't know how old these sensors are, but I might try cleaning them to see if that makes them more consistant between banks. Am I correct in assuming the after-cat sensors should always be reading low voltage indicating very lean?

I also noted that on many sites the O2 sensors for AEL models are cheaper than the ones for non-AEL models; are they different types of sensors? Is the wide VS 1 volt a AEL VS non-AEL thing?