MoT fail on emissions
Discussion
It's that time of year again - my 136000 mile Citroen AX has failed it's MoT on emissions, there are a couple of other problems but the emissions are the deal-breaker. The recorded numbers are:
Engine - 954cc single-point injection
Run 1
Value Max limit My car
RPM 2550 2188
CO % 0.300 0.594
HC 200 141
Lambda 1.030 1.046
Run 2
Value Max limit My car
RPM 2550 2229
CO % 0.300 0.655
HC 200 122
Lambda 1.030 1.035
The HC and Lambda readings are not far off a pass but the CO seems very high.
I checked the spark plugs and all are a uniform pale biscuit colour and were changed about 10000 miles ago. Last year the car failed for the same reason but a new catalytic converter and lambda sensor cured the problem and the car passed.
I will change the air filter, any other suggestions?
Engine - 954cc single-point injection
Run 1
Value Max limit My car
RPM 2550 2188
CO % 0.300 0.594
HC 200 141
Lambda 1.030 1.046
Run 2
Value Max limit My car
RPM 2550 2229
CO % 0.300 0.655
HC 200 122
Lambda 1.030 1.035
The HC and Lambda readings are not far off a pass but the CO seems very high.
I checked the spark plugs and all are a uniform pale biscuit colour and were changed about 10000 miles ago. Last year the car failed for the same reason but a new catalytic converter and lambda sensor cured the problem and the car passed.
I will change the air filter, any other suggestions?
Did you fit a genuine cat or one of the cheaper pattern ones?
If it was the latter then that may be the problem.
Had just that with a 306, passed with a NEW pattern cat but failed 12 months later. Fitted a secondhand genuine one - from a 306 we had scrapped - & the emissions dropped to virtually zero.
The pattern one was slightly under half the size of the genuine.
Discussion with the tester is that its a common issue with the pattern ones - fine when new but don't last.
If it was the latter then that may be the problem.
Had just that with a 306, passed with a NEW pattern cat but failed 12 months later. Fitted a secondhand genuine one - from a 306 we had scrapped - & the emissions dropped to virtually zero.
The pattern one was slightly under half the size of the genuine.
Discussion with the tester is that its a common issue with the pattern ones - fine when new but don't last.
There are some tests you can perform on the lambdas using a multi-meter. Well worth doing, as a sensor might have gone down. They're only cheap too, aslong as you're good at splicing wires! Likewise with the cat - I read that if you use a thermo gun, the temp on the exiting side of the cat should be 50degrees lower than the entry side. If it's much different, the cat isn't performing as it should.
Secondly, check the manifold to downpipe gasket isn't leaking. This can play havoc with the sensor's readings, as it recieves a weaker signal as some gas is being lost to atmosphere, so it instructs the ECU to richen the mixture. The three bolt triangular flange on the exhausts is prime candidate for warping and leaking slightly. Sometimes it's so slight you can actually tell with your hand next to it, and the only way is to load the engine up (you can normally hear it). Or fill the TB with Redex and fire it up with someone placing their hand on the exhaust.....the white smoke will find it's way out of any less than perfect joint
Secondly, check the manifold to downpipe gasket isn't leaking. This can play havoc with the sensor's readings, as it recieves a weaker signal as some gas is being lost to atmosphere, so it instructs the ECU to richen the mixture. The three bolt triangular flange on the exhausts is prime candidate for warping and leaking slightly. Sometimes it's so slight you can actually tell with your hand next to it, and the only way is to load the engine up (you can normally hear it). Or fill the TB with Redex and fire it up with someone placing their hand on the exhaust.....the white smoke will find it's way out of any less than perfect joint
stevieturbo said:
Often car dealers are known for supplying genuine car parts.
Cheers Stevie, that one had completely escaped me...much as when I wanted to buy a 60 watt light bulb and found that they and Woolworths had gone the way of the Dodo.To be honest I wondered whether the Citroen dealer network would stock parts for a car of that age but perhaps parts are common to the Saxo so I'll give it a try, if not then local motor factor followed by the scrap yard.
100SRV said:
Cheers Stevie, that one had completely escaped me...much as when I wanted to buy a 60 watt light bulb and found that they and Woolworths had gone the way of the Dodo.
To be honest I wondered whether the Citroen dealer network would stock parts for a car of that age but perhaps parts are common to the Saxo so I'll give it a try, if not then local motor factor followed by the scrap yard.
AX cats are very similar to Saxo ones, though not a direct fit. You could probably get one of those, or a 106 one to fit with some adjusting, but it's not really needed. Avoid any other type of TU engined car's catalyst - they start to differ massively. To be honest I wondered whether the Citroen dealer network would stock parts for a car of that age but perhaps parts are common to the Saxo so I'll give it a try, if not then local motor factor followed by the scrap yard.
Your best bet is a local exhaust supplier. Bosal cats are good quality (they make some of the OE ones) and will save you a raping at the dealer.
Kitchski said:
AX cats are very similar to Saxo ones, though not a direct fit. You could probably get one of those, or a 106 one to fit with some adjusting, but it's not really needed. Avoid any other type of TU engined car's catalyst - they start to differ massively.
Your best bet is a local exhaust supplier. Bosal cats are good quality (they make some of the OE ones) and will save you a raping at the dealer.
Thank you Kitchski,Your best bet is a local exhaust supplier. Bosal cats are good quality (they make some of the OE ones) and will save you a raping at the dealer.
just happens that my local motor factor has a stock O.E. quality catalytic converter in stock at £105 versus £380 for OEM, I will check who the manufacturer of the cheaper one is.
I think the small engined AX uses the Bosch Mono-Jetronic system which relies very heavily on the correct operation of the lambda sensor (since they use only throttle angle and RPM for load sensing - AKA "Alpha-N"). First check is to make sure the sensor is switching; it may only be 12 months old but cheap pattern sensors can have a very short life.
Mr2Mike said:
I think the small engined AX uses the Bosch Mono-Jetronic system which relies very heavily on the correct operation of the lambda sensor (since they use only throttle angle and RPM for load sensing - AKA "Alpha-N"). First check is to make sure the sensor is switching; it may only be 12 months old but cheap pattern sensors can have a very short life.
Hiand thank you - I will inspect this tomorrow with my multimeter...thank you for the suggestion. When does/should the MIL illuminate on this type of EFi system?
100SRV said:
Mr2Mike said:
I think the small engined AX uses the Bosch Mono-Jetronic system which relies very heavily on the correct operation of the lambda sensor (since they use only throttle angle and RPM for load sensing - AKA "Alpha-N"). First check is to make sure the sensor is switching; it may only be 12 months old but cheap pattern sensors can have a very short life.
Hiand thank you - I will inspect this tomorrow with my multimeter...thank you for the suggestion. When does/should the MIL illuminate on this type of EFi system?
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