Question for all the nct emissions experts

mlmcelligott

I put a 1998 vw passat through the nct last week and it failed on emissions. Its a 1.6 petrol with only 70k miles on it. It passed the low idle but failed on the high idle with a mark of 70%. I think the fail rate was for anything over 30%.

Ive plugged in the diagnostic tool but im not getting any fault codes. The car is regularly serviced but had an issue with running rich when I first got it nearly 2 years ago. A new MAF sensor solved that problem.

The car is only used as a run to and from work so is only driven for about 15 miles a day on country roads and for about 10 minutes each way so maybe the engine isn't heating up fully before it completes its journey.

I put in some of that anti smoke petrol additive that i got in a motor factors about an hour before the test to try to reduce the emissions but it didn't work. It was red hot going through the test though

Any ideas where the fault might be? I dont really want to spend crazy money on a new catalytic converter when it mightn't be the problem.

itarumaa

What are the values the car failed on,

CO/HC/LAMBDA ?

You can find that info from nct paper, and those results might give more info about the cause of the problem.

mlmcelligott

CO 0.75 vol% and it's supposed to be less than .30%. The lambda was 1.02 (0.97 - 1.03) and the HC was 132 ppm (less than 200)

Any ideas?

itarumaa

Both values, CO and HC are bit high,

what was the engine/oil temp when the car was tested,

If the car is in good condition, timing belt, oil, coolant etc then I would go a warm-up drive before the test and try again, before doing anything else.

Changing a catalytic converter should be the last step to think about, not the first. Before that you should at least check spark plugs and air filter,

but getting the car warm up properly would be the first option, assuming that the car is in good condition.

mlmcelligott

The car is in good condition alright. It was just serviced with new oil, plugs and oil & air filters.
It was at 87 degrees during the test and had driven for about 30 minutes before it. We had noticed that its been a bit heavier on petrol in the last few months though.

Timing belt was done at 60k last year too.

Andrew Campbell

the CO value is linked to the ratio of fuel to air mixture. a high CO is caused by too much petrol and not enough air. usual cause is a blocked air filter. If you're certain its OK then possibly the coolant temperature sensor is faulty or there is some series resistance in its connections (have I lost you yet?) try and disconnect and reconnect each electrical connection associated with the fuel injection system. this can eliminate the series resistances and bring a value just out of tolerance back within the limits. then unless you have a CO meter you'll need to get it checked again to see if you've improved things

mlmcelligott

Already connected it to the diagnostic machine and no codes were recorded. I heard of there being a common problem with the temperature sensor. Would the diagnostic tool not find this fault if there was one? where in the engine is it located so i can disconnect it and reconnect it again.
Should i disconnect and reconnect all the sensors while the engine is running or just with the ignition on?

mlmcelligott

Just had a look there on micks garage and it says that my 1.6 petrol doesnt have a temperature coolant sensor. Could you link me to one?

The GF just told me that the heating has gotten really hot too in the last few months. You could burn your hand on the hot air the blower is blowing out when it heats up. It never used to be that hot before, any relation to the coolant sensor?

mlmcelligott

I took the car out for a drive last night and heard a whistling noise coming from the engine under acceleration. Its not there at idle at all.

After doing a little bit of searching I found someone had the same issue and said it could be a vacuum leak in either the hoses or the inlet manifold.

Andrew Campbell

mlmcelligott wrote: »

Would the diagnostic tool not find this fault if there was one?
Not if its giving a within range reading but the wrong one

where in the engine is it located so i can disconnect it and reconnect it again.

Not certain but usually in the cylinder head or thermostat housing

Should i disconnect and reconnect all the sensors while the engine is running or just with the ignition on?

Its best to do this with the ignition off to avoid erroneous fault messages but as you have the reset tool .......

hope this helps

Andrew Campbell

mlmcelligott wrote: »

J


The GF just told me that the heating has gotten really hot too in the last few months. You could burn your hand on the hot air the blower is blowing out when it heats up. It never used to be that hot before, any relation to the coolant sensor?

hot heater is not usually regarded as a fault, is the temp indicator on dash in the red, any sign of coolant loss, any overheat warnings? IMO these are not related to the original fault

mlmcelligott

No, temp gauge always reads about 90 when heated up, car never over heats and has never needed the coolant topped up.

Forgot to mention the brake pedal is very stiff too and the brakes arent as effective as before. Coupled with this strange whistling noise im thinking its a mechanical fault like a breather valve or cracked hose and not something electrical as I'm not getting any codes.