Discussion
Hi
Another year, another MOT trying to get the car through the emissions test, and just a few questions to the more knowledgeable.
The AJP has a dispensation in the MOT for an increased lambda reading to 1.2. This seems to be the only official nod to the problems the car has getting through the emissions test on the MOT. I just have a little bit of trouble wrapping my head around an MOT fail and what the likely course of action should be.
I assume the dispensation for the Cerb was to be allowed to run a higher lamda and the lower figure is unchanged from standard. This means that the Cerb is allowed to have a weaker mixture coming out of the exhaust than a standard car.
This seems to disagree with the respected tuners on here that the Cerb was originally fuelled very rich on the standard map.
I again assume therefore that the valve overlap In the engine is effectively weakening the mixture in the exhaust which is why TVR needed the dispensation in the first place.
Is that right?
Another year, another MOT trying to get the car through the emissions test, and just a few questions to the more knowledgeable.
The AJP has a dispensation in the MOT for an increased lambda reading to 1.2. This seems to be the only official nod to the problems the car has getting through the emissions test on the MOT. I just have a little bit of trouble wrapping my head around an MOT fail and what the likely course of action should be.
I assume the dispensation for the Cerb was to be allowed to run a higher lamda and the lower figure is unchanged from standard. This means that the Cerb is allowed to have a weaker mixture coming out of the exhaust than a standard car.
This seems to disagree with the respected tuners on here that the Cerb was originally fuelled very rich on the standard map.
I again assume therefore that the valve overlap In the engine is effectively weakening the mixture in the exhaust which is why TVR needed the dispensation in the first place.
Is that right?
my cars only just passed the MOT. It was more from the point of understanding the engine.
Lower lambda toward the 0.9 level should release more power form the engine as it is slightly on the richer side of combustion which is where I would have thought TVR would need its dispensation especially as the default map is known to be rich. To have my car over the last few years showing good HC/CO emissions therefore indicating good combustion but increasing lambda mean that probably air is getting in somewhere and I ought to preventatively look for it prior to the next MOT.
I just thought it was an area I don't really understand because there are a few contradictions which don't make sense to me.
Lower lambda toward the 0.9 level should release more power form the engine as it is slightly on the richer side of combustion which is where I would have thought TVR would need its dispensation especially as the default map is known to be rich. To have my car over the last few years showing good HC/CO emissions therefore indicating good combustion but increasing lambda mean that probably air is getting in somewhere and I ought to preventatively look for it prior to the next MOT.
I just thought it was an area I don't really understand because there are a few contradictions which don't make sense to me.
Higher Lambda readings at the tailpipe, ie as read at an MoT Test, are nearly always because of a hole/poor joint in the exhaust, air is being drawn in so the readings will show an abnormally high O2 figure. In this instance it does not mean that the engine is running lean.
"I'm sorry Sir, but your car has failed the MoT because the exhaust is too clean!"
"I'm sorry Sir, but your car has failed the MoT because the exhaust is too clean!"
TwinKam said:
Higher Lambda readings at the tailpipe, ie as read at an MoT Test, are nearly always because of a hole/poor joint in the exhaust, air is being drawn in so the readings will show an abnormally high O2 figure. In this instance it does not mean that the engine is running lean.
"I'm sorry Sir, but your car has failed the MoT because the exhaust is too clean!"
That is undeniably a possibility, but you have skilfully dodged the actual question which is why did TVR get a dispensation for lambda values at the exhaust while running their engines rich on the map."I'm sorry Sir, but your car has failed the MoT because the exhaust is too clean!"
Surely you aren't suggesting TVR got an exemption for lambda because the engines in the TVR factory couldn't do up the bolts on the exhaust?
Just for the record these were the limits and actual values at my last MOT:
Measure Limit Values Measured
CO 0.3% 0.19
HC 200ppm 28
Lambda 0.9 to 1.2 1.02
Very similar figures to everyone else except mine is an S6, but the same limits apply to all S6 engines.
Interestingly the Griff 500 has the normal tighter limits and suprised me by being cleaner:
Measure Limit Values Measured
CO 0.2% 0.00
HC 200ppm 5
Lambda 0.97 to 1.03 1.00
So a very good question from the OP!
Measure Limit Values Measured
CO 0.3% 0.19
HC 200ppm 28
Lambda 0.9 to 1.2 1.02
Very similar figures to everyone else except mine is an S6, but the same limits apply to all S6 engines.
Interestingly the Griff 500 has the normal tighter limits and suprised me by being cleaner:
Measure Limit Values Measured
CO 0.2% 0.00
HC 200ppm 5
Lambda 0.97 to 1.03 1.00
So a very good question from the OP!
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