Volkswagen Golf IV - Golf Mk4 2.0 8v - Emissions Fail - Advice Please

Honest John Back Room » Technical matters
View Threaded
Mon 23 Jul 2012 21:56
Volkswagen Golf IV - Golf Mk4 2.0 8v - Emissions Fail - Advice Please - alex80

I suspect this is going to be a head off fix and not economicaly worth while. Would really apprechiate some advice...

177K on the clock, always been quite heavy on oil. Took for a hard run a few days before MOT (nice black cloud at first acceleration - it's mainly doen city miles this last year) but seemed fine after.

No fault codes to be read via OBD. Could do with an oil change but I should think these numbers are too far out for that to make much difference. May have had slight leak around one of the exhaust connections pre MOT but came back from test with obvious blowing sound and now extremly juddery at idle (whole car shaking). Honest garage who I've always used without issue I really doubt they did anything though they did seem to run it for quite a while and hard (just making sre it was nice and hot)

Failed on:

CO2 1.33%

HC 2541 (!) ppm

LAMBDA 1.21

aside from emissions all OK.... Clearly now needs the exhaust fixed but that's not the core problem. Can't afford to spend much on it specutavily.. is there anything cheap I should check before saying goodbye

many thanks

Reply | Report as offensive | Link
Mon 23 Jul 2012 22:46
Volkswagen Golf IV - Golf Mk4 2.0 8v - Emissions Fail - Advice Please - unthrottled

It's running way too rich. Try disconnecting the lambda sensor, MAF sensor and Coolant temperature sensor one by one. I'd bet that one of them is sending duff readings to the ECU which is then overfuelling. Hopefully, when you isolate the faulty sensor, the ECU will be able to 'guesstimate' the correct fuelling (which it can do fairly accurately). The juddering should then stop. Then replace the relevant sensor and try for a retest.

If it has been running rich for a long time, the extra fuel could have washed the bores down-leading to ring wear and hence heavy oil consumption. The only cost effective bodge is to use a heavier grade of oil than the specified one. 20W50 is a favourite for worn engines. Don't lose heart just yet!

Edit. Pull the spark plugs to see if they are a uniform colour-in your case a sooty/shiny black. If you have a cylinder misfiring, then that would give pretty awful emissions readings.

Edited by unthrottled on 23/07/2012 at 22:56

Reply | Report as offensive | Link
Mon 23 Jul 2012 23:03
Volkswagen Golf IV - Golf Mk4 2.0 8v - Emissions Fail - Advice Please - injection doc

Lambda is very high ! this tells me that iether the MOT stations analyzer as a small air leak in the pipe or you have a pin hole in the exhaust near the front of a vacum pipe leaking ! this will also make it run too rich !

Simples

Reply | Report as offensive | Link
Mon 23 Jul 2012 23:12
Volkswagen Golf IV - Golf Mk4 2.0 8v - Emissions Fail - Advice Please - unthrottled

Ha ha! Yes Doc. I assumed the leak was near the back box, but if it was at the front, it would play havoc with the lambda readings. Hopefully simples indeed!

Reply | Report as offensive | Link

Looking for a garage you can trust? Honest John's Good Garage Guide has thousands of reader recommended garages, plus how-to guides and tips on servicing.

The Good Garage Guide