Not just another Emissions failure question :)

redbeaard

Well I hope it isn't.

Short question. If I’ve replaced the Air Flow Meter, the CAT and the lambda sensor and it’s still hopelessly failing, what are other possible causes.

Bought a 2000 1.6l Golf mk4, 2 years ago which came with new NCT. 6 months later it started giving trouble - stalling occasionally and was fluctuating during idle. Local garage couldn’t find fault so went to VW garage who hooked it up to computer and found it was the Air Mass Meter. No other problems detected.

1st NCT about a year ago
Low idle (1,070 rpm) -- CO 0.65 (fails above 0.50) HC 460 ppm (fails above 0 ppm)
High idle (4,550 rpm) -- CO 10.04 (fails above 0.30) HC 1,416 ppm (fails above 200 ppm)
Lambda = 0.7 (fails if not between 0.97 and 1.03)
During the high idle test a spark plug blew so I had to drive home on 3 cylinders. There is one spark plug on the golf that is very hard to access so I guess whatever lazy feicker serviced it previously hadn’t bothered to change it. Replaced it the next day and it seemed to be running fine again.

2nd NCT weeks after first
Low idle (751 rpm) -- CO 10.22 -- HC 1,231ppm
High idle (2,700 rpm) -- CO 10.22 -- HC 1,231 ppm
Lambda = 0.71
Is it weird that the low idle and high idle values are exactly the same? I didn’t notice until I had left the test centre so I couldn’t question them on it.

3rd NCT a year later (believe me I’ve got good excuses for not getting it done sooner)
Before test the CAT was replaced. Got one second hand from a scrap yard that has a very good reputation.
Low idle (820 rpm) -- CO 7.77 -- HC 898 ppm
Lambda = 0.78
Test called off during high idle due to excessive exhaust smoke.

4th NCT weeks later
Replaced lambda sensor with new sensor
Low idle (820 rpm) -- CO 0.65 -- HC 563 ppm
High idle (2,820 rpm) -- CO 9.91 -- HC 1,522 ppm
Lambda = 0.71
Test called off during high idle due to excessive exhaust smoke.



So now here I am. Since replacing the CAT the problem has obviously gotten worse as now they can't even complete the test but I can't really be sure if that's due to new CAT being crap or not installed properly or if it's something else that has just gotten worse in the year since it was last tested.

I suppose I have to go to VW garage to get it put on the computer again but I'm a little reluctant as that'll be 80euro just for that. Is there anything I can check out before that like holes in exhaust, cracked head gasket, that type of thing?

teediddlyeye

Hydrocarbons and CO seem very high. Could burning a lot of oil. Check for excessive blue smoke when you rev it.

braddun

did you change all the spark plugs and the wires then

chaeck egr valve and the map sensor


you can buy car readers for 20 euros

Chimaera

Lambda low and CO and HC high mean your car is running absurdly rich and if your mechanic or VW didn't spot this, it's time to find someone else to work on your car.

When was the air filter last changed?

How is the coolant temperature sensor? VW tend to use a dual element sensor: 1 element sends the signal for the temp gauge, and the other sends the signal to the ECU. One can fail without affecting the other. I'd have this checked. The ECU will adjust the mixture according to coolant temperature and if it's getting the wrong info it could be enriching the mixture unnecessarily.

Manifold leaks are unlikely to be the cause (they usually result in the car leaning out) but it's worth checking for.

Is the timing belt in good shape?

I'm not sure there's much point buying a code reader in this case. The diagnostic work required needs VAG specific diagnostics. I'd find a good indy who has proper diagnostics and get them to sort it out. If you're near Port Laoise, user George Dalton here operates a garage there with an excellent reputation.

redbeaard

Thanks for the replys. Lots to think about.

teediddlyeye wrote: »

Hydrocarbons and CO seem very high. Could burning a lot of oil. Check for excessive blue smoke when you rev it.

It is going through a lot of oil. I must look to see what colour smoke it is.

braddun wrote: »

did you change all the spark plugs and the wires then

He did change the sparks but I don't know about the wires. Can the wires cause this much effect?

Chimaera wrote: »

When was the air filter last changed?

TBH I don't know so in other words not since I got it. I guess this would be effected by when I was driving with the bad air mass meter so therefor could be badly clogged up alright! I'll look at this asap but I do relise it's not going to solve my problems.

Chimaera wrote: »

How is the coolant temperature sensor? VW tend to use a dual element sensor: 1 element sends the signal for the temp gauge, and the other sends the signal to the ECU. One can fail without affecting the other. I'd have this checked. The ECU will adjust the mixture according to coolant temperature and if it's getting the wrong info it could be enriching the mixture unnecessarily.

I had no idea about this. Will it be picked up by the VAG diagnostics?

I probably should have said, there was 80k miles on the clock when I got it and I've put on another 20K since. I got the timing belt done somewhere around the 65k or 70k but I can't remember now if it was before or after the first round of NCTs last year.

I've been going to a local guy (west coast Donegal here) to get a lot of this work done. He's old school but has a very good reputation. He has the simple code reader but wouldn't be too quick to use it if you know what I mean. There is only one garage with the emissions tester anywhere near here (and he's 30min drive) and he doesn't want to know about you unless your a regular customer, he said he's fed up people giving out to him when he can't track down a problem in a few hours. And the VW garage don't want to know about you if you come in with anything over 10 years old.

So that's where you guys come in, thanks again

Special Circumstances

Quantify the oil usage. In my barstool opinion, your engine is goosed , it's not uncommon for VW 1.4 1.6 engines to start using a lot of oil. Is the "excessive exhaust smoke" blue or more black?

Now, maybe it is fixable, but your current mechanic options would seem to involve trial and error replacement of parts. Could get expensive with no real guarantee of success.