Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Some clues welcome

I don't want to be pedantic, but I suspect these are different problems. The downstream sensors, as in Peter's case, have purely a control function. They simply monitor whether the catalytic converter is working properly. Mostly it is connected to the DTC 420.
https://www.obd-codes.com/p0420
With OBD2, you can see in real time if the lambda sensor downstream is bouncing or level. If it is bouncing, the catalytic converter is not working properly. But that means the probe is ok, just showing bad news.

It seems plausible that the catalytic converter does not reach its working temperature to cause this fault. A sporty driving style is a countermeasure as in Peter´s case. Or the catalytic converter is faulty. All this has no influence on the engine performance as long as the cat is not blocking the airstream (I had this case with my Elise when the internal grids were pushed to the output pipe of the cat).

DTC 133 refers to the engine control and concerns the upstream sensor(s).
https://www.obd-codes.com/p0133

On my 4/4 this upstream sensor was faulty after 80,000km and the DTS was reported in OBD2 (but not in the MIL!, Ford is very "tolerant" there). A new sensor resulted in better performance and significantly less fuel consumption. It is also possible that the MAF sensor is not working properly or that there is a leak in the upstream gas pipeline (intake and/or outtake) that is giving the wrong values to the sensor. Then it tries to readjust, and it can happen that the engine always runs too rich, which unfortunately contributes to the probe getting dirty, a vicious circle. This could also be the reason why your sensor, meabh, is defective again after so few miles.

I would also look at the MAF sensor and check all connections from the air intake to the lambda sensor for leaks. Because, to me, it sounds like an undetected fault, and therefore and a new S1 sensor again could probably be both...the causal fix or unfortunately just a temporary symptom improvement.

If you can, try very carefully cleaning the MAF sensor with a special spray that won't break anything. This would be the cheapest and easiest point of a start. Also clean the electrical plug with a appropriate spray (let it dry before reconnecting). You can e.g. read your OBD2 when just switching on the ignition with cold! engine if the MAF sensor shows a plausible environment temperature or not, but this is only one of the MAF´s jobs).

My Plus8 with Gems management used to have the MIL occasionally come on.
My OBD meter showed “random intermittent misfire” as the reason. I checked the plugs( low mileage ) , leads, connections on sensors but it would occasionally come back. I switched to V-Power and it stopped. The only time it returns is if I have used 95 octane for a few tank fulls. I have also put a simple heatshield round the cats to help keep them in best operating temp. A single layer of Aluminium with stainless straps, no extra insulation.
Meabh, your MIL is on when the same sensor is the culprit? I doubt it is the MAF. I would concentrate on that sensor and double check the connections, wiring. It might also be worth making some shielding to reduce airflow round that area as it may overcool that sensor?

Okay Heinz. I will start with cleaning the MAF sensor.
Out of interest, the front bank upstream sensor was very black when I took it out two days ago. I have cleaned it as best one can.
Interesting that the MOT didn't pick up on it re: emissions.

meabh, just if you have read my first version, I added: Also clean the electrical plug with a appropriate spray (let it dry before reconnecting). You can e.g. read your OBD2 when just switching on the ignition with cold! engine if the MAF sensor shows a plausible environment temperature or not, but this is only one of the MAF´s jobs).

Heinz,

Stay tuned: I need to buy the appropriate torx bolt remover which I will do next week BUT I did remove the electrical plug from The MAF whilst the engine was running and it did not stop. I thought that it would stop. All he other MAF related indicators, e.g difficult to start, rough idle, hesitant acceleration are not present.

meabh, if you remove the electrical contact from the MAF sensor, the engine will continue to run...but in the emergency setting, so without any sensor data at all, and in a way that nothing breaks...much too fat. You only do that in an emergency for short distances. Otherwise your Lambda sensor is very dirty again after a short period of time.

Yes, get the right spanner. Remember that the plastic used by Ford is very cheap and screw the MAF back on very carefully after cleaning. You only have to look crooked and the plastic threads are broken at Ford.
What you can try now is to clean the electrical contact of the MAF and let it dry. And delete all errors that are now certainly stored because the engine was running without the MAF.
Also clean the electrical contacts of the lambda sensor cables. Even a very small contact resistance will cause these sensors to work incorrectly.

Thank you Heinz I will attend to this on Monday

Heinz, Sospan,

Thank you again for your input. Brett Syndercombe at BHM has also been very helpful and has contacted the factory too on my behalf but they had nothing new to add. I am experimenting: Looking back at the service sheets before I bought the car shows that this front bank sensor was changed before at around 4000 miles. I changed it at 8000. My experiment was to use an extender to remove the sensor from the exhaust stream and drive to Toulouse and back. There was a noticeable change in that; the engine ran at 2000 rpm on start up and quickly settled down to 900 rpm, Before it would run fast for at least five or six klms and it would sometimes run fast at odd times. That stopped completely. The engine management light did not come on at all. Everything operated as normal, smooth running, strong acceleration, 38 mpg. Next I removed the sensor and extender and replaced them with just the old sensor I had previously removed at 8000 miles. This one had been soaked in petrol and had been sprayed with contact cleaner and left to dry overnight. So far the. OBD reader shows no codes. It remains to be seen how long this lasts.

Sospan, You doubt that the MAF is at fault and I tend to agree as there have never been starting issues, or hesitation under load or acceleration.

The exhausts are not blackened which would be the case if it was running rich due to excess fuel being fed as a result of perceived lean running. I cannot detect any leaks from the exhaust, or from vacuum pipes. The CT (MOT) did not pick up any aberrations.

Stay tuned I guess.