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Discussion Starter · #1 ·
Having failed the UK MOT on emissions 2.5% CO I finally manged to get the codes read.The garage that did the test recommended a new Cat.
The codes are 17916 Idle sys.learned value upper limit attained,16518 o2 sensor No activity detected,16519 o2 sensor circ,sensor 1 malfunction.

As I had change the sensor last year I thought this couldn't be the problem.However I had changed the can cover gasket recently and used RTV gasket sealer on it and recently marginally overfilled the engine oil level.

Can either of these have killed the o2 sensor? Is the first fault code showning that the upper value limit attained showing the the fuelling is too rich ,I have no idea what the fist code means

Any help would be much appreciated
 

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run an O2 sensor test with a scope or a voltmeter and check the connection before replacing the cat. if its dead in the lean direction (which it sounds like) then car is going nuts trying to add fuel. but at 2.5% CO post-conversion it's already *way* too rich. CO should only be like 0.5% when it's running right (14.7:1 A/F) and even lower with air injection.

At 2.5% that's like 10.5:1-12.5:1 A/F ratio! must be getting pretty bad mileage.

Did they test any other gases or just CO?
 

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Discussion Starter · #3 ·
The UK test only requires the HC CO and Lambda to be measured.The HC was within spec(Below 200ppm) but the Lambda was 0.93 (the low range limit is 0.97).

Is it possible for a cat to correct the CO from 2.5% to below 0.3 % the UK spec .

I have tried measuring the voltage but the reponse time of the meter is not quick enough.It seems to stay around 0.5v (but does go up to 0.7 when bliping throttle).How do you make the engine go lean without doing things like pulling of injector leads?

Interestingly the mpg figures have not changed at all the ,the pre 1992 cat CO allowance in the UK was 2.5%

Also does anyone know if you can destroy a O2 sensor by using siliconce RTV on the cam coveri.e I need to know if I need to take it all apart and clean it.
 

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I think your cat is ok and it's just an A/F issue. lambda of 0.93 ~ 13.5:1 A/F which is too rich. Here is a table:
Lambda- Air Fuel Ratio (petrol)

0.70 10.3
0.75 11.0
0.80 11.8
0.85 12.5
0.90 13.2
0.95 14.0
1.00 14.7
1.05 15.4
1.10 16.2
1.15 16.9
1.20 17.6
1.25 18.4
1.30 19.1
1.35 19.8
1.40 20.6
1.45 21.3
1.50 22.1
1.55 22.8
1.60 23.5

take a look at the charts in this article (page 2), it explains the relationship of the gasses to A/F.

http://www.motorage.com/edindex/1200feat1.htm

note that at your lambda value the CO is ~2-2.5%, and that simply by making lambda closer to 1 the CO value drops rapidly.

*edit* sorry dead link
 

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Discussion Starter · #7 ·
Silcone sealer and 02 sensor

Thanks for the help guys .I will remove the old cam cover gasket and clean all traces of the orange RTV.

I shall let you know the result



On the Euro/Uk model there is only one O2 sensor,it change about 400 cars later it changed to 2 .It does make diagnosis of the cat much easier. However I guess with a new sensor the lamba and CO should come into or very close to spec

This was on one of the sites you recommended,an MR2 site.
What will damage my O2 sensor?

Home or professional auto repairs that have used silicone gasket sealer that is not specifically labeled "Oxygen sensor safe", "Sensor safe", or something similar, if used in an area that is connected to the crankcase. This includes valve covers, oil pan, or nearly any other gasket or seal that controls engine oil. Leaded fuel will ruin the O2 sensor in a short time. If a car is running rich over a long period, the sensor may become plugged up or even destroyed. Just shorting out the sensor output wire will not usually hurt the sensor. This simply grounds the output voltage to zero. Once the wiring is repaired, the circuit operates normally. Undercoating, antifreeze or oil on the *outside* surface of the sensor can kill it. See how does an Oxygen sensor work. [/b]
 

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Discussion Starter · #8 ·
Problem solved it was the lambda (O2 ) sensor, the OBD codes were as described.
Thanks to the garage for reading them and then telling me the Catalytic converter needed replacing.As I thought they either no nothing about emissions or more likely were trying to rip me off for £400 for a new CAT.
The old sensor was only a year old ,but was manufactured by LUCAS (the Prince of Darkness) I have learnt my lesson and replaced it with a Bosch OEM from VW :p
 

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Discussion Starter · #10 ·
:) Fuel consumption has improved especially on long runs on the motorway.Now I can get nearly 40mpg at 65mph on a 30 mile run previously strugged to get to 34 .NB this is a N/A car and driving with A/C off(not required much in the UK!) 1 person and driven very gently with virtually no changes in speed i.e no acceleration

Thanks for yr help guys :wink:
 
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