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Tin top emissions
Benzine - 8/11/12 at 05:14 PM

Our VW Polo (6n2 1.6 petrol) has just failed it's MOT test. Mostly little jobs (Number plate light, headlight aim) but the emissions are way out/borderline comical HC. Is it possible to tell what's wrong from the emissions print out? I'm wondering if I need a new cat or lambda sensor.



The car seems to be driving fine, I did an mpg check only a couple of weeks back and it was normal.

froggy - 8/11/12 at 06:46 PM

prime suspect would be lambda sensor ,is the engine management light on ?

Benzine - 8/11/12 at 07:08 PM

quote:
Originally posted by froggy
prime suspect would be lambda sensor ,is the engine management light on ?


No warning lights on at the moment. I'd rather it was a lambda sensor than a car, local scrapyard has about 5 Polos in that I could get sensors for pennies.

steve m - 8/11/12 at 07:29 PM

A replacemnt lambda my be in order, but when i have had an issue or fail, an itallion tune up is in order
that is after an oil change and a new airfilter

but ive never had figures that high! so possibly the cat has failed?

steve

Benzine - 8/11/12 at 08:43 PM

quote:
Originally posted by steve m
A replacemnt lambda my be in order, but when i have had an issue or fail, an itallion tune up is in order
that is after an oil change and a new airfilter

but ive never had figures that high! so possibly the cat has failed?


Yeah could be the cat, I've done an oil and filter change and air filter (which was terrible!) but I've not had such high figures before either. My old Volvo 740 failed emissions as it had been sat for 5 years, the petrol looked like tizer and that was about 2% CO I think. New petrol, oil change and it flew through. The garage has offered the use of their exhaust gas analyser whenever I want so I might try an Italian tune up and see if that helps the figures.

Another thing I changed was the dizzy cap and rotor arm, the contacts were really pitted and jagged. Since doing that the car starts much quicker. Not sure if that'd have an effect or not

[Edited on 8-11-2012 by Benzine]

froggy - 8/11/12 at 08:48 PM

For the co to be that high the lambda is dead , seen plenty of cats recover with a good caning .

britishtrident - 8/11/12 at 09:03 PM

Those are very high co readings it looks to me like over fueling probably because the engines isn't running closed loop.

The first thing to do is check for leaking vacuum hoses or any leaking joints in the inlet manifold.
Check all the connections to the various sensor MAP ( orif fitted MAF ) and the TPS.
The second thing is check the engine is getting fully up to working temperature --- ie not just "N" on the gauge.
I would also look at the spark plugs a check for any signs of a cylinder running rich which might indicate a leaky injector.
To tell if the engine is running closed loop you really need to look at output from the lambda sensor either by looking at live OBD or connecting a DMM directly to output of the sensor

skodaman - 8/11/12 at 11:31 PM

Ah so you're the cause of all this global warming and there's me blaming China.

Benzine - 9/11/12 at 03:45 PM

thanks froggy and britishtrident, I'll look into those things suggested

quote:
Originally posted by skodaman
Ah so you're the cause of all this global warming and there's me blaming China.


whoops

Benzine - 19/11/12 at 05:46 PM

update (tech problem threads without a solution are a pet hate)

passed MOT retest today. I've not picked it up yet so i'm not sure how it's emissions figures were. In the end I did an oil, oil filter, air filter, dizzy cap and rotor arm change, as well as lamdba sensor. I left the cat alone and gave it a well spirited drive before retest. I was expecting a b0rked cat so quite pleased (except being ill and bored in bed all day)