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[addy]

Took the wifes car for MOT today, the CO emissions are just slightly higher than the recommended MOT one.  What could be causing it?

The tester said the Lambda is in range.

Thanks in advance for any help.

[Raeturbo]

I would check air filter clean and gap plugs,  then put a good quality injector cleaner in warm it up and give it a damn good ragging works surprisingly well.

[addy]

Got the results in front of me. It failed on First and the second high idle test, but not idle.

Natural idle
RPM 790 PASS
CO .376  PASS

First fast idle
RPM 2846 PASS
CO .530
HC 81 PASS
LAMBDA 1.021 PASS

Second fast idle
RPM 2864 PASS
CO .530 FAIL
HC 80 PASS
LAMBDA 1.019 PASS

I thought the LAMBDA reading was supposed to be 1?  Do these readings point towards bad O2 sensor and/or Cat? I notice on live data, before it went for test, that the Sensor would go to Open Loop every now and then, at idle even with engine warm. Have cleaned the MAF with the proper cleaner.

[Raeturbo]

Huh it passed with .530 first time and failed with .530 second time sorry but I don’t understand that?

[Raeturbo]

As you more than likely know high co is due to incomplete combustion so that’s the way to go anyway

[addy]

sorry it failed CO emissions of .530 on both Fast idle tests.

I would have thought it would of been the other way, fail on normal idle test and pass on fast idle, as the engine is working faster so burning fuel quicker at higher revs, or am I thinking wrong?

I changed spark plugs and airfilter before going.  The old spark plugs looked OK, no contaminates normal colour.  According to charts online the plugs are fine and engine in good condition.

[dave the builder]

from 19th edition emissions book......
 max is
0.5% Co normal idol ,
 0.3% fast idol ,
 200 ppm hydrocarbons ,
 Lambda range 0.97 to  1.03
OIL at 80 degrees plus ,which is important
if the car is not up to temp ,it will overfuel badly
if the coolant temperature sensor is duff (common on 4 bangers) it will overfuel (so check live data )
I put cataclean in 1/4 of a tank of petrol, with spirited drive,or later gear changes to rev move,get the cat warm ,then put fresh petrol in before test ,
lambda may be duff or the temp sensor ,car should not go open loop once it is in closed loop
getting the cat really hot prior to mot would probably have seen a pass , your not far off
I'd check live data again if possible, temp sensor and lambdas ,possibly replace them, cataclean ,check and gap plugs, check breathers are clear,throttle body is clean, and get the car warm ,cats hot (Mexican tune up) before taking for re-test at a set appointment , i say this because if the car sits waiting for an hour before test,it will go cold . 

[Raeturbo]

Agree that should do it worth a try before you spend

[deviator]

if the coolant temperature sensor is duff (common on 4 bangers) it will overfuel (so check live data )

This. There are 2, one for the dash and one for the ECU. The ECU one is the important one. Does the car get up to and hold temp properly?

[Nick W]

if the coolant temperature sensor is duff (common on 4 bangers) it will overfuel (so check live data )

This. There are 2, one for the dash and one for the ECU. The ECU one is the important one. Does the car get up to and hold temp properly?

agreed. Live data is your best bet, but the parts(I'd replace both to be sure) are cheap and easily changed on a 4pot so are probably worth changing anyway. Poor temperature sensors will affect fuel economy, so changing one will pay for itself.

[deviator]

if the coolant temperature sensor is duff (common on 4 bangers) it will overfuel (so check live data )

This. There are 2, one for the dash and one for the ECU. The ECU one is the important one. Does the car get up to and hold temp properly?

agreed. Live data is your best bet, but the parts(I'd replace both to be sure) are cheap and easily changed on a 4pot so are probably worth changing anyway. Poor temperature sensors will affect fuel economy, so changing one will pay for itself.

I will add, I think this is one of those parts were I would only buy genuine.

[addy]

Rang Vauxhall dealer who said the Temp sender for the ECU, Part NO. 90411977 is no longer available. just to find out how much it would cost, incase it is the problem  

The one on the engine is blue, and I understand that there is also a black one.

So will have to look else where. Will it be a Bosch or Siemens make? If unable to find one in which ever it is, what make would be the next best?

[deviator]

https://www.genuinepartsearch.co.uk/ <--- they are saying they have a genuine packaged part. I would just confirm it's vauxhall packaged and not cheap variant. IE Genuine Fram.

Also, another part number (same part) 1342850

[Diamond Black Geezer]

Used these many times before they buy ex-dealer stock, never any issues before, can recommend them 

[addy]

Rang Genuine parts, to check if genuine or OEM. They said it is genuine Vauxhall Sensor, so purchased one. Cost £15.87 including postage.

Thanks for thelp. Much apprecited.