Relation between CO, Hydrocarbons and Lambda Reading on MOT
Discussion
Can anyone kindly tell me what is the direct relation between lambda reading and the CO and Hydrocarbon reading? If hydrocarbons and CO readings at fast idle are at 0 but the lambda reading is above the max limit what is the actual lambda reading? is it measuring something or is it a calculation?
For the calculation see here:
https://www.bridgeanalyzers.com/service-calibratio...
If the lambda is high then the engine is (or appears to be) running lean. I would guess you either have a faulty lambda sensor causing it to run lean or a leak in the exhaust pipe *after* the lambda sensor, so the engine is running correctly but excess oxygen is getting into the exhaust pipe through the leak and throwing off the exhaust gas analyser.
https://www.bridgeanalyzers.com/service-calibratio...
If the lambda is high then the engine is (or appears to be) running lean. I would guess you either have a faulty lambda sensor causing it to run lean or a leak in the exhaust pipe *after* the lambda sensor, so the engine is running correctly but excess oxygen is getting into the exhaust pipe through the leak and throwing off the exhaust gas analyser.
ta264 said:
For the calculation see here:
https://www.bridgeanalyzers.com/service-calibratio...
If the lambda is high then the engine is (or appears to be) running lean. I would guess you either have a faulty lambda sensor causing it to run lean or a leak in the exhaust pipe *after* the lambda sensor, so the engine is running correctly but excess oxygen is getting into the exhaust pipe through the leak and throwing off the exhaust gas analyser.
Thank you. I have new Air Fuel Ratio sensors (well not new but changed a few years ago) and also changed the post-cat o2 sensors as well at that time. There is no lean or rich codes on the ECU or anything and car runs what appears to be perfectly normal. I do suspect there might be a leak somewhere between where the exhaust leaves the engine and before the post-cat sensors because it sounds rather loud under that area but I just cannot see any visual leak. https://www.bridgeanalyzers.com/service-calibratio...
If the lambda is high then the engine is (or appears to be) running lean. I would guess you either have a faulty lambda sensor causing it to run lean or a leak in the exhaust pipe *after* the lambda sensor, so the engine is running correctly but excess oxygen is getting into the exhaust pipe through the leak and throwing off the exhaust gas analyser.
Are you able to see the lambda values as read by the car? If there's a leak before the post-cat sensor you'd expect to see that show up in the lambda as measured by the car. What were the values as read by the MOT?
A neat trick I stole from youtube when tracking an exhaust leak was to get a wet & dry vacuum cleaner with a "blow" setting and gaffer tape this into the exhaust pipe. When you turn it on it'll blow air up the exhaust, pressurising it a little. If there are any leaks the air will blow out of the leak. If you spray soapy water over the exhaust you'll quickly see where the air is escaping. Much safer trying to find a small leak this way than with a hot exhaust.
A neat trick I stole from youtube when tracking an exhaust leak was to get a wet & dry vacuum cleaner with a "blow" setting and gaffer tape this into the exhaust pipe. When you turn it on it'll blow air up the exhaust, pressurising it a little. If there are any leaks the air will blow out of the leak. If you spray soapy water over the exhaust you'll quickly see where the air is escaping. Much safer trying to find a small leak this way than with a hot exhaust.
ta264 said:
Are you able to see the lambda values as read by the car? If there's a leak before the post-cat sensor you'd expect to see that show up in the lambda as measured by the car. What were the values as read by the MOT?
A neat trick I stole from youtube when tracking an exhaust leak was to get a wet & dry vacuum cleaner with a "blow" setting and gaffer tape this into the exhaust pipe. When you turn it on it'll blow air up the exhaust, pressurising it a little. If there are any leaks the air will blow out of the leak. If you spray soapy water over the exhaust you'll quickly see where the air is escaping. Much safer trying to find a small leak this way than with a hot exhaust.
Yes I can plug in diagnostics and read what the car is reading Lambda at and i'll report back later this evening. The value read at the MOT were 1.091 at first and then 1.092 at second. With HC and CO being 0 both times.A neat trick I stole from youtube when tracking an exhaust leak was to get a wet & dry vacuum cleaner with a "blow" setting and gaffer tape this into the exhaust pipe. When you turn it on it'll blow air up the exhaust, pressurising it a little. If there are any leaks the air will blow out of the leak. If you spray soapy water over the exhaust you'll quickly see where the air is escaping. Much safer trying to find a small leak this way than with a hot exhaust.
ta264 said:
Are you able to see the lambda values as read by the car? If there's a leak before the post-cat sensor you'd expect to see that show up in the lambda as measured by the car. What were the values as read by the MOT?
A neat trick I stole from youtube when tracking an exhaust leak was to get a wet & dry vacuum cleaner with a "blow" setting and gaffer tape this into the exhaust pipe. When you turn it on it'll blow air up the exhaust, pressurising it a little. If there are any leaks the air will blow out of the leak. If you spray soapy water over the exhaust you'll quickly see where the air is escaping. Much safer trying to find a small leak this way than with a hot exhaust.
Far simpler to stick one end of a length of tube in one ear and track over the suspected area with the other end... you'll soon find the epicentre of the noise.A neat trick I stole from youtube when tracking an exhaust leak was to get a wet & dry vacuum cleaner with a "blow" setting and gaffer tape this into the exhaust pipe. When you turn it on it'll blow air up the exhaust, pressurising it a little. If there are any leaks the air will blow out of the leak. If you spray soapy water over the exhaust you'll quickly see where the air is escaping. Much safer trying to find a small leak this way than with a hot exhaust.
ta264 said:
Are you able to see the lambda values as read by the car?
OK so the car ECU readout is giving Lambda readings as 1.000 on Bank 1 and 0.998 on Bank 2. I've located to tiny holes just after the post-cat O2 sensors. Literally just after the o2 sensors as the pipe is heading out to the backbox there is a tiny hole that I cannot see but i can feel puffs of hot air coming out of it. Could this be the culprit? Any recommendation of bandage or putty systems to seal these up?Gassing Station | Home Mechanics | Top of Page | What's New | My Stuff