Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing O2sensors and cylinder relationship

Seems that I recently read, in a thread response, of a relationship between the cylinder numbers and the O2 sensors on the V-8 engines. I've searched around for it, but to no avail.
I could be dreaming as well.

O2 sensors surely just on each exhaust manifold so four on a V6/V8 before and after each CAT if fitted.

That is how I understand it.

Just one or two on earlier systems - 1 per CAT...

Yes that's it, mine has a dual system with one per Cat as Graham says

Note mine is a 1999 - we don't know what year yours is ? just in case there were changes in the time honoured Morgan style

My 2002 car has a dual exhaust with sensors before and after the cats on each side.
4 sensors in total. All identical so no pre andpost cat differences. Gems management system.
The ecu monitors emissions for each bank of 4 cylinders, so bank1 and bank2. From memory bank 1 is the left hand side with odd number cylinders(1,3,5,7). Bank 2 is the other side with even numbered cylinders (2,4,6,8).

The sensor pre-cat is used by the ECU to set the correct fuel/air mix and the sensor after, or at the rear end of the cat is to check the correct functioning of the cat. If it has a reading outside the standards set it will throw an error and normally will light the MIL (Malfunction Indicator Light), otherwise known as the "engine check light). It can be reset with a suitable OBD tool.
Torque Pro for Android being a pretty good example https://play.google.com/store/apps/details?id=org.prowl.torque

Yes, my 94 +8 has two O2 sensors one before each cat. My Moggy doesn't want to know or care how the cat is functioning

Last week on the way to Italy my oxygen sensor, before the cat, gave up the ghost, I was already at the Austrian border. I have no explanation for this other than age and wear. The only special thing was that we were in hot sunny weather 1.5 hours in stop and go on the German highway. The error occurred when I could really give full throttle again for the first time after the traffic jam. It was, as in Germany also, not possible to get a sensor in a store, not in Merano and not in Trento. Today everything is bought online, also the repair garages have nothing in spare stock. Very understandable when you see the variety of sensor models. But mostly the voltage jump sensors differ only in cable length and plug shape. Error code P0030, so really the oxygen sensor was faulty and not an indirect other error like false air. I could also see in the live diagram that the voltage jump no longer succeeds. I was worried about the engine because I could not order a sensor in a short time beeing underway. I also wanted to keep the issue small so that we could enjoy the vacation as a group and not suddenly focus on the repair.

The emergency run can be much too rich so that nothing is broken by uncontrolled lean stage. But you should drive it only a short time. But I still had 1,800 km ahead of me. Judging by the consumption, the engine did not run much too rich, about 6.0 liters per 100km. Of course, it may be that the dynamics of the mix control does not adequately adapt, in other words, you can have phases that are too lean and other phases that are too rich. Now I am happily back home. My 4/4 didn't let me down although it's a queasy feeling to drive with limited engine control for so long, especially in long tunnels. The camshaft timing was disabled, the power was felt at 80 hp instead of normal 145 hp. I drove the engine very gently and always left it in the mid-range. Tomorrow I'll install the new sensor that has already arrived, as I need to get a slotted oxygen sensor nut or a 22 wrench first.

The front sensor is the important one as it signals to the ecu to alter fuel input to manage emissions. On the Gems system the rear one ( after the cat) is basically to check the cat is functioning properly. If emissions ( based on Oxygen level in the exhaust gas) are within limits then the dar should run ok. The system puts the MIL on if the rear one has problems. On my car the fault code shown was an open circuit in the downstream sensor heater circuit ( after cat) sensor. Basically the heater gets the sensor up to functioning temperature quicker than waiting for the exhaust to heat it.
Older systems did not have this heater but it was added later to get faster functioning to reduce emissions a bit more and quicker. A fine tuning method.
My OBD check tool gave the code P1193 which, for Rover/Land Rover is the downstream heater circuit open, hence not working. Car ran OK with no issues as the upstream ( front) sensors were OK.