Emissions Fail (High Lambda) and oil temp (low voltage)
Posted: Thu May 04, 2023 12:31 am
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!
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!