Failed MOT on CO Emission: Grateful for advice

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couchiedemon

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Hi Folks, I got some bad news today. My Disco 1 3.9i failed it's MOT today on emissions (and a track rod end, which is easy to fix). The test refusal cert says "Exhaust Emissions Carbon Monoxide content after 2nd fast idle excessive (7.3.D.4)".

The CO readings at both fast idle tests are as follows:

1st 0.653%

2nd 0.386%

All other readings at both idle tests were passes.

I was advised to use a fuel system cleaner and give it a good thrash just prior to the next test. I have put in a can of fuel cleaner, however, this seems a bit hit n miss.

The disco has 70K miles on clock and was last serviced at 64500 miles.

Anyone out there got any ideas of how I can ensure that the CO reading is down for the next test? Any advice gratefully recd.
:confused:
 
Check to see if the lambda sensors are working correctly. They should switch between roughly .5 and 4.5v very quickly at idle.
 
With titania sensors? I assumed the D1 used a 5v reference same as any other titania equipped car?

Whereabouts are you, OP?

There are only a few things that can cause poor CO readings and they centre around your air fuel ratio -it's either running too rich or too lean. Often as not the engine itsself is fine, it's a sensor telling the engine that it isn't fine and it's believing that sensor and adjusting to suit the false reading. However if it's been running out of spec for too long then it can damage the catylitic converter. This may well have happened, but if it was a faulty lambda sensor causing the rich condition, then you will damage any new cats you fit. Hence you need to check the condition of the lambda sensors asap. The only reliable way to do that is with a scope - an error code will only be thrown if the sensor is a long way out of spec, it won't detect a slow sensor.

Whereabouts are you?
 
Last edited:
No,its the Gems equipped engines that use 5-0v Titania.The 14CUX on RRC's and D1's are 0-1v Titania.Then the K series in FL1 and later Bosch injected v8's use the cheaper 0-1v Zirconia's. Sad that I know such boring stuff,good that I can remember....
The Titania sensors give a much cleaner waveform than the Zirconia's,so you should be OK watching their output on a DVM.Scope is nice,but not everyone can get access to them.
 
sidewaysste said:
With titania sensors? I assumed the D1 used a 5v reference same as any other titania equipped car?

Whereabouts are you, OP?

There are only a few things that can cause poor CO readings and they centre around your air fuel ratio -it's either running too rich or too lean. Often as not the engine itsself is fine, it's a sensor telling the engine that it isn't fine and it's believing that sensor and adjusting to suit the false reading. However if it's been running out of spec for too long then it can damage the catylitic converter. This may well have happened, but if it was a faulty lambda sensor causing the rich condition, then you will damage any new cats you fit. Hence you need to check the condition of the lambda sensors asap. The only reliable way to do that is with a scope - an error code will only be thrown if the sensor is a long way out of spec, it won't detect a slow sensor.

Whereabouts are you?
Click to expand...

Just a thought but if the system wer operating out of spec and the cat were damaged presumably the Hydrocarbon reading should be elevated, but the HC reading was within tolerance. I might just start off by giving it a good service, change the oil, plugs, filters and possibly the Sensors before I go to get it tested again (aftyer a good long thrash down the A21).
Tks for the advice. I'm in Sevenoaks, Kent.
 
Last edited:
eightinavee said:
No,its the Gems equipped engines that use 5-0v Titania.The 14CUX on RRC's and D1's are 0-1v Titania.Then the K series in FL1 and later Bosch injected v8's use the cheaper 0-1v Zirconia's. Sad that I know such boring stuff,good that I can remember....
The Titania sensors give a much cleaner waveform than the Zirconia's,so you should be OK watching their output on a DVM.Scope is nice,but not everyone can get access to them.
Click to expand...

Sad? possibly, but useful to know. I had thought titania sensors were all 5v reference but then I'd only actually looked at my Disco which is a gems engine. You live and learn I guess.

OP, Unburned HCs are usually from the engine running rich. Get the sensors checked then if necessary replace them, if your MOT tester is friendly he will do an emissions test before doing a full retest. you'll then know if you need a cat or not.
 
sidewaysste said:
OP, Unburned HCs are usually from the engine running rich.......
Click to expand...

Test results were:
fast idle tests
first Benchmark results
CO <=0.300% 0.653% Fail
HC <=200ppm 28ppm pass
Lambda 0.970-1.030 0.992 pass

Second
CO Same as above 0.386% Fail
HC ----"--- 19ppm Pass
Lambda ---"--- 0.992 Pass

Natural idle
CO <=0.500% 0.016% Pass

So if I understand it right, this would suggest that the HC output is actually good and the ECU is not over-fuelling. If that's the case would there be any value in changing the Lambda sensors?
 
couchiedemon said:
Test results were:
fast idle tests
first Benchmark results
CO <=0.300% 0.653% Fail
HC <=200ppm 28ppm pass
Lambda 0.970-1.030 0.992 pass

Second
CO Same as above 0.386% Fail
HC ----"--- 19ppm Pass
Lambda ---"--- 0.992 Pass

Natural idle
CO <=0.500% 0.016% Pass

So if I understand it right, this would suggest that the HC output is actually good and the ECU is not over-fuelling. If that's the case would there be any value in changing the Lambda sensors?
Click to expand...

Not in my opinion. I would service the car, then remove the air filter just before the test rendez-vous. Make sure it's fully up to temp as well.

I suspect it your car was run again it might have passed, as the results were moving in your favour.


Dave
 
Not that it matters but why have a second Fast Idle Test? is that not a full Cat Test from 2002 onwards

My disco is BET tested so just the one Fast idle test, two months ago I had the test with the results as follows.

Fast Idle Test
CO 0.00 pass is <0.20
HC 10ppm pass is <200
Lambda 1.01 pass is between 0.97 1.03

Natural Idle Test CO 0.00 pass is <0.30

The CO and lambda has never changed, HC has varied over the years but that was only by 6 ppm once (16 max) which I believe is due engine temp and or fuel quality used, normally for years now it's been 10 to 12ppm.
 
couchiedemon said:
Test results were:
fast idle tests
first Benchmark results
CO <=0.300% 0.653% Fail
HC <=200ppm 28ppm pass
Lambda 0.970-1.030 0.992 pass

Second
CO Same as above 0.386% Fail
HC ----"--- 19ppm Pass
Lambda ---"--- 0.992 Pass

Natural idle
CO <=0.500% 0.016% Pass

So if I understand it right, this would suggest that the HC output is actually good and the ECU is not over-fuelling. If that's the case would there be any value in changing the Lambda sensors?
Click to expand...
No,not at all.Nor will removing the air filter help.The engine is clearly running closed loop off the oxygen snesors and the HC figures show the cats are working well.Its running just slightly rich.Here is where an oscilloscope would really help,the Co is only slightly high - so a partial misfire is the most likely cause.A tracking plug lead or fouled plug is probably all that is wrong.When were the leads last changed ?
 
couchiedemon said:
Hi Folks, I got some bad news today. My Disco 1 3.9i failed it's MOT today on emissions (and a track rod end, which is easy to fix). The test refusal cert says "Exhaust Emissions Carbon Monoxide content after 2nd fast idle excessive (7.3.D.4)".

The CO readings at both fast idle tests are as follows:

1st 0.653%

2nd 0.386%

All other readings at both idle tests were passes.

I was advised to use a fuel system cleaner and give it a good thrash just prior to the next test. I have put in a can of fuel cleaner, however, this seems a bit hit n miss.

The disco has 70K miles on clock and was last serviced at 64500 miles.

Anyone out there got any ideas of how I can ensure that the CO reading is down for the next test? Any advice gratefully recd.
:confused:
Click to expand...

Where are you in the world? I may well have a piece of kit which can look at your o2 sensors
 
eightinavee said:
No,not at all.Nor will removing the air filter help.The engine is clearly running closed loop off the oxygen snesors and the HC figures show the cats are working well.Its running just slightly rich.Here is where an oscilloscope would really help,the Co is only slightly high - so a partial misfire is the most likely cause.A tracking plug lead or fouled plug is probably all that is wrong.When were the leads last changed ?
Click to expand...


Thanks for all the help chaps. I dnk when the leads were last changed (only owned this since the summer) but I think I will change them when I do the service, so that it's got new oil, oil filter, air filter new plugs and leads. Hopefully that will do for any errant misfire and she'll get through the test.
 
Whilst you're at it change the distributor cap and arm. Use genuine parts as aftermarket ones are crap. Use Magnecor KV85 ignition leads. They are expensive, but reliable.
 
couchiedemon said:
Thanks for all the help chaps. I dnk when the leads were last changed (only owned this since the summer) but I think I will change them when I do the service, so that it's got new oil, oil filter, air filter new plugs and leads. Hopefully that will do for any errant misfire and she'll get through the test.
Click to expand...

I did all of the above and only just scraped through on 2nd fast idle test. Still a pass is a pass but will probably need to replace the cats this year. Tks to all who chipped in with help/advice.
 
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