MK5 Golf NCT emissions failure?

reccit

Hey,

Can anyone help me out on a general diagnosis for my car, an 05 1.6 petrol mk5 golf.

Failed the NCT on CO emissions;

High idle @2990 rpm 0.86% - pass is 0.2%

Plugged it into friend's vcds and got the following -

2 Faults Found:
16555 - Fuel Trim; Bank 1
P0171 - 006 - System Too Lean - Intermittent
Freeze Frame:
Lambda: 25.0 %
Lambda Factor: 1.008
Voltage: 0.440 V
Speed: 0.0 km/h

16688 - Cylinder 4
P0304 - 009 - Misfire Detected - Intermittent
Freeze Frame:
RPM: 640 /min
Mass Air / Rev.: 92.7 mg/str
Temperature: 88.5°C
Lambda: 1.2 %
RPM: 2592 /min
Mass Air / Rev.: 397.9 mg/str
Temperature: 82.5°C
Lambda: 11.7 %


The car was sitting up for a while before the test, although it did get a good spin beforehand.

Thanks

Kopparberg Strawberry and Lime

I'd go for an oil change, filter, plugs and air filters And lambda sensor and throw it back in and see tbh.

A fresh tank of fuel too. Maybe run it right the way down and throw 40 -50 into her

John.G

Not familiar with this particular engine but it may have a PCV (positive crankcase ventilation) valve connected via a small hose into the throttle body, due its position, if any leaks, it can cause the problems above so check this out carefully for any splits as these can be difficult to spot, I came across one (with a split) which was causing all sorts of problems when cold but the engine ran perfectly when heated up as the drop of oil (when hot) being pulled in by the PCV was sealing the split in the bottom of the hose. The independent garage concerned had replaced almost everything but fair play to them they gave a few free services when shown the piece of pipe.

reccit

Failed again this morning!! It had a service <500km ago and I checked the air filter, it's perfect. I ran the tank right down, threw in a litre of dipetane and 3/4 full of fuel, got the engine good and hot.

CO failing this time was even higher than the last. Does this look like the cat? Reluctant to drop a few hundred quid unless it will be sorted.

CO 1.3% - pass 0.2%
Lambda 0.97 - pass not between 0.97 and 1.03

It also didn't fail on the Lambda last time.

John.G

The cat will have nothing to do with it if you are getting misfires (probably due to lean mixtures) and lean mixtures.
Suggest also removing the brake servo hose at the manifold and plug the manifold port and take another VCDS scan.

Kopparberg Strawberry and Lime

Might need someone else to confirm this but did your lambda pass ?

It has major next to it suggesting it failed but the reading is 0.97.

I'm at a lose on that one anyway if it isint the lamda sensor. A new exhaust / cat will only disguise what issue is there very temporarily.

whizbang

You are supposed to run out the dipetane and refill with fresh fuel before test. Probably whats thrown the Lambda reading outside the limit.

But you still have a problem with mixture;

A lambda of .97 would indicate an air/fuel ratio of 14.259:1 (derived by multiplying .97 by 14.7).

- rich mixture,meaning you have too much fuel or not enough air. The misfire on Cylinder 4 could cause this by not burning off the fuel.
An overreading airflow sensor, or your own lambda sensor overreading could possibly also, but sort the misfire first.

mk7r

It needs a cat