Elan S2 MOT emissions fail - CO too high
Discussion
Hello all, I am looking for some help diagnosing the root of this issue with my step-dad's 1992 Elan S2 Turbo. The car is completely standard, with 106k miles on it, regularly serviced and starts and runs well.
It's just been in for an MOT, CO was initially 6%, adjustment of the potentiometer (I assume this measures throttle position?) has reduced it to 3%, but it has not been possible to use this method to get below the 1.5% CO requirement. It's with a well-trusted garage but they are not Lotus specialists (and there are none nearby).
I wondered if anyone with experience of the S2 could suggest a good starting point for fixing the problem, my thoughts were O2/lambda sensor (or sensors?), cat, ignition system in that order. Does that sound sensible or are there any other known issues which could cause this?
Many thanks!
It's just been in for an MOT, CO was initially 6%, adjustment of the potentiometer (I assume this measures throttle position?) has reduced it to 3%, but it has not been possible to use this method to get below the 1.5% CO requirement. It's with a well-trusted garage but they are not Lotus specialists (and there are none nearby).
I wondered if anyone with experience of the S2 could suggest a good starting point for fixing the problem, my thoughts were O2/lambda sensor (or sensors?), cat, ignition system in that order. Does that sound sensible or are there any other known issues which could cause this?
Many thanks!
A 1992 registered car won't be an S2 nor will it have an O2 sensor or a cat. It's fully open loop, with the CO set as you have found with the pot near the ECU. The pot is a standard Ford part and they can go faulty.
A very long time ago (mid 90's?) when the issue of CO levels arose Lotus did a memcal swap service so that the engine calibration actually met the MOT requirements, this involves removing the ECU, breaking the seals and unplugging the memcal assembly that has the limp home calibration and the memory for the normal calibration, Then you plugged the new one in, reinstalling and setting the CO, then sending the old memcal back to Lotus who them desoldered the memory and installed a new prom for the next customer.
Not sure if this mod ever made it into the service bulletins, if it did an enquiry at an official dealer might possibly yield results.
But I'd hazard a guess this swap service is no longer available and everyone at Lotus that knows anything about this is long retired.
If you have access to a Tech 1 or the DIY Elanscan you would be able to read the ECU cal number, if it doesn't match what is in the ECU manual then the mod might have been carried out (but I'm not 100% sure if the cal ID changed)
A very long time ago (mid 90's?) when the issue of CO levels arose Lotus did a memcal swap service so that the engine calibration actually met the MOT requirements, this involves removing the ECU, breaking the seals and unplugging the memcal assembly that has the limp home calibration and the memory for the normal calibration, Then you plugged the new one in, reinstalling and setting the CO, then sending the old memcal back to Lotus who them desoldered the memory and installed a new prom for the next customer.
Not sure if this mod ever made it into the service bulletins, if it did an enquiry at an official dealer might possibly yield results.
But I'd hazard a guess this swap service is no longer available and everyone at Lotus that knows anything about this is long retired.
If you have access to a Tech 1 or the DIY Elanscan you would be able to read the ECU cal number, if it doesn't match what is in the ECU manual then the mod might have been carried out (but I'm not 100% sure if the cal ID changed)
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