Emissions Fail (High Lambda) and oil temp (low voltage)

[Superdunx]

Good evening forum,

I'm seeking some help/guidance on a problem with my 2000 reg MGF VVC which is running MEMS2J. Every year I have had it so far I have had an emissions drama at MOT time. First year, high Co (new cat fitted), last year very high HC (complete top end refurb, new rings and liners at great cost from an MG specialist). This years fail is high lambda. the car has now been off the road for 2 months and its driving me mad. Car is standard 143vvc other than a pipercross filter in an MGTF airbox, 52mm throttle body, piper manifold and a TT Mk7 backbox

For some time before the MOT I had an occasional and intermittent issue where it seemed as though the car would suddenly run rich. Usually after a long motorway run or when in slow traffic - I always put this down to 'heat soak' The symptoms are that it would lack low end performance, not idle and stalled and was difficult to restart, but once restarted the fault would always appear to 'clear'

Using the rovermems diagnostic tool I was able to extract the fault codes from the ECU. I had two persistent errors relating to the oil temperature sender 'Engine Oil temp low voltage' and 'engine oil temp present' and on relating to (I assume) the O2 sensor 'feedback historic'. I was able to clear the feedback error, although it did reappear after a drive, the oil temp ones though are persistent and cannot be cleared. I had not managed to get to the bottom of this before MOT time so off it went and failed for lambda not being controlled. Co and HC were well within limits on the first test.

Following the first fail, the garage found that the body of the lambda sensor was damaged and the sensor partially hanging out. A new sensor was fitted and the car resubmitted to the test centre, but it failed again on lambda, and this time the Co being slightly too high also.

So I have a car that seems to run rich, giving me a high lambda (usually indicative of lean burn), an error with the oil temp sensor (that from the Rover literature appears to play no part in air fuel mixture calculation and is only there for VVC actuator oil viscosity) and a car that seems to not want to operate in closed loop despite all of the sensors giving sensible values (yes even the oil temp sensor values look sensible despite the error). It makes no sense! I have so many questions about the logic within the MEMS2J unit. Could it be the learnt adaptive settings needing time to adjust or a reset to defaults after the lambda sensor replacement? what is a 'low voltage' error on the oil temp sensor and why does it not change if the sensor is disconnected? what are the specific conditions that the ECU is looking for before it goes into closed loop?

I'm getting quite desperate to get this fixed so any suggestions, guidance or help would be very much appreciated! Many thanks in advance!

[Charless]

I wonder what the actual new lambda reading is - pscan shows 0.49v on mine with live data averaging. It wouldn't be the first fail straight out of the box. I too had a MEMS2J lambda which managed to damage itself in a well protected location and the replacement didn't last a year.
Much was made of the adaptive learning ECU in the early days but from the sound of your situation the car hasn't had much road mileage to learn and adapt since the problem was discovered.
There is also the possibility that the unclearable oil temp fault codes point to internal failure within the ECU (2nd hand unit replacement is not hugely expensive).
Sorry yours is struggling but do update this interesting thread when you nail the problem.

[CSix]

I'm having the exact same problem on my 97 reg (MEMS2J). Seems to be running extremely rich and failing on high CO and Lambda and I have no idea what's going on, I'm at my wit's end.
Although I haven't been able to put it on a diagnostic scanner since I don't have a pScan for these pre obd ECUs.
I've literally done everything imaginable except the oil temp sensor because the gauge works fine so I'm wondering reading this if it's worth a go.

My only suggestion would be to give the engine earth strap a good clean and check the wiring for the oil temp senso isn't damaged

[CSix]

https://www.the-t-bar.com/forum/roverli ... ions-guide

[Superdunx]

So a quick update - thanks to everyone who has posted. I have opened a new thread as I could not find this one earlier, but progress has been made even if I still have no MOT pass yet!

So the oil temp low voltage error was the VVC cam period decrease solenoid connector and the oil temp sensor cables swapped. These connectors are mechanically compatible so fit in both the correct and incorrect positions. Consequently the oil temp was constantly measuring across an 8ohm solenoid coil giving a fixed low voltage on the ECU oil temp line, which is why the fault could not be cleared.

Having fixed this I then had an oil temp voltage high error. The sensor is a negative temp coefficient thermistor, so having found the sensor data it stated 2 kohm at 20C - mine was measured at 40k ohm so the wrong sensor! it even had BMW written on it

It seems that the wrong sensor was also a different colour (black instead of brown), which is likely how the connectors probably got switched. On the MGF the sensor was brown with a brown connector. The VVC decrease solenoid is black and has a black connector. Later MGTF's had a black sensor with a black connector and a black vvc solenoid with a brown connector (heaven knows where the logic is in that!) so seeing the black sensor someone must have assumed logically the colours match the sensor/solenoid colours, which it does when the correct sensor is fitted.

So the engine now runs fine, the VVC mech seems to be increasing and reducing cam period when revved and the oil temp sender is giving a correct value and no error in the fault code memory.

I am still having issues though which I have opened another thread to discuss, but at least its progress!

Csix its worth checking this on yours as it could well be your issue. Happy to send some pics of the connector configuration if this helps? I'm using the RoverMEMS software which is a cheap tool for non OBD MEMS systems. Its useful even if some of the data its providing is a bit odd/questionable, and may be a good tool to get if you need to communicate with MEMS 2J.

Charles its good to know that my ECU was not at fault - I do have a spare but need to find someone who can code it for the Immobiliser and reset to base MGF map. I am considering having one standard and sending another to SAWS tuning to get it 'chipped', but need to get it through its emissions test first!

Best regards,
Duncan.

[Charless]

Well investigated and thanks for the forum feedback - I'll bet yours isn't the only one!

[Roverlike]

In your other thread: viewtopic.php?f=8&t=26692&p=202407#p202407
I wrote you following:

Have you tried to disconnect plugs from two (2) Solenoid Control Valves and make measures without them connected?
In case you have measurements orrect now, then you just need to change both solenoid control valves.
Disconnecting plugs from them will limit rpms to 5000, but that is just to test how engine behaves in such situation.