General mot emissions

[irabbit]

sorry for asking this question again but i am stumped.

first mot test gave me readings as below:


fast idle:
co 0.478 fail
hc 72 pass
lambda 1.01 pass

2nd fast idle:
co 1.387 fail
hc 488 fail
lambda 1.129 fail

natural idle
co 0.647 fail

after test i did an oil / filter change.
changed plugs and leads.
used wynns emissions reducer.

2nd mot test:

fast idle:
co 0.49 fail
hc 83 pass
lambda 1.01 pass

2nd fast idle:
co 0.46 fail
hc 59 pass
lambda 1.01 pass

natural idle
co 0.47 pass


does anyone have any ideas please.

 

[rallycinq]

Did you change the air filter?

Do you have an exhaust leak? Put a rag in your hand and try and stop the exhaust to check.

Cheers

PD

 

[irabbit]

hi pd.thanks for quick response.
i have blocked tailpipe and checked all pipework but no leaks.
i also put new halfords air filter in.
the co levels seem constant on second test between 0.46 and 0.49.
also lambda reading doesn't change.
mot tester says it could be anything. as i have now spent £150, i am anxious to resolve problem but mechanic just suggests fitting part after part with no guarantee.

i would be happy if someone said spend £100 on whatever and it will pass but garage non-commital.

jon.

 

[spedo]

Having carried out the advice already given, and you are happy that the vehicle is is in good state of service and the exhaust is not leaking you may have to suspect-

1. Engine temp sensor, fault causing over enrichment pushing up your CO2 limits.
2. The lambda sensor, not so likely as you lambda is mostly within limits 0.97-1.03, however it still could be sending faulty info back to the ECU.
3. The caterlistic converter, least likely and quite expensive.

If it were me I would double check all my vacuum tubes for leaks, and if need be secure with small clips.

Next I would change the temp sensor. There are other things to check out like the MAP sensor voltages and security of the plug wireing. I always start with the easyest and cheapest options first.

 

[irabbit]

thanks for reply.
i am going to check vacuum hoses tonight.
are there just 2 of these and can i test them by removing and seeing any change in running ?
also how would i test map sensor and temp switch ?
thanks in advance for any help.
jon.

 

[spedo]

The temp sensor is quite cheap to replace, however if you don't mind the hassel and you have a volt meter that can read ohms and a half decent thermometer then hear goes-

TEMP SENSOR

1. Take out the temp sensor
2. Get a pan of water ready to boil
Now the tricky bit
3. Suspend the tip of the temp sensor in the water, connect the ohms meter accross the two pins at the end of the sensor and observe the approx resistance values thus-

Deg C ------- Restance ohms
0 ------------ 10000
10 ----------- 7000
20 ------------4000
30 ----------- 3000
40 ----------- 1800
50 ----------- 750
80 ----------- 330
90 ----------- 200

MAP (plug removed) Has 3 pins.

Teminals plug end. Switch off ignition. disconnect MAP plug. Switch on ignition to get the lights up and test-
First and middle pin 5v approx. First pin and earth 5v approx. If voltage not as expected check wireing .ie. earth connections.

MAP operation (plug connected)

You need to devise a way of back probing the wires to carry this operation out. I use special clips a £25.00 a pair, however if you don't have these get some needles, pearce the insulation just to make contact,
lay them flat and secure a wire to each with a small croc clip. Make sure you dont short the wires out.

Switch on ignition and check voltage between the middle and end pin which should read 4.5 volts approx.

Start engine and alow to idle. The voltage accross the same pins should be 1.5 volts approx.

Good luck.

 

[irabbit]

thanks very much. i will try that tonight.
jon

 

[Madmike]

after test i did an oil / filter change.
changed plugs and leads.
used wynns emissions reducer.

2nd mot test:

fast idle:
co 0.49 fail
hc 83 pass
lambda 1.01 pass

2nd fast idle:
co 0.46 fail
hc 59 pass
lambda 1.01 pass

natural idle
co 0.47 pass


does anyone have any ideas please.

Am I missing something here?
Seems like you passed 2nd time round Jon??

 

[irabbit]

hi. it failed 2nd test on co at 0.46 but passed on lambda.
jon.

 

[spedo]

Fast idle = 2500-3000rpm max CO2 allowed is 0.3

 

[RuiG]

Just out of curiosity.

Was the engine hot/warm when you did the readings? Especially first one. Sometimes we stand for too long waiting for MOT and engine gets too cold. I always leave mine working and try to go for a 30m run before tests.

Readings between cold and hot engines can be very different. In your 2nd fast iddel engine should be hotter and it gave better reading.

 

[ycming]

before every mot, change oil and filter, spark plug, loads of redex with super unleaded from any petrol company and just blast it everywhere!!!!!

Never had a cinq fail on emission before!!

Ming

 

[irabbit]

engine was hot before both tests and had wynns emission reducer in.
just started car with lambda sensor disconnected at electrical plug and there was no difference in running.
does this mean sensor needs replacing or is it just a coincidence do you think.

 

[rallycinq]

Lambda sensor is out of circuit until it warms up.

Cheers

PD

 

[irabbit]

hi. i just drove car to warm it up and then disconnected lambda. there was no change in engine running whilst driving. i think this means lambda not working but not sure ?

 

[rallycinq]

Did the injection light come on?

Cheers

PD

 

[irabbit]

no injection light and no noticable change in anything else.

jon.

 

[rallycinq]

strange.

The ECU should notice the 02 sensor missing.

I presume the light comes on with the ignition.

Cheers

PD

 

[irabbit]

yes comes on with sensor plugged in.

 

[spedo]

strange.

The ECU should notice the 02 sensor missing.

I presume the light comes on with the ignition.

Cheers

PD

Rallycing does this sensor incorporate a heater element (H02S)?
Irabbit has it got 2 or 3 wires comming off the sensor?