7A cold start and CO% problems

[Azimut]

hmmm.

Where are you measuring the CO from?

On the tubular manifold there is a CO measuring point PRE CAT. MOT people never use it but i wonder if setting the correct reading there would = an MOT friendly reading at the back?

it was from the exhaust pipe ofcourse not from manifolds measuring hole.

[steve briance]

It makes no difference on my car as i have no Cat but for you, your 'MOT' CO reading may well be different to what is coming out of the test pipe, its not by chance that the Lambda probe is before the Cat...

The idle and CO need setting together as one affects the other and it is a kind of balancing act.

I understand your frustration - if everything indicates there is no fault then WHY DOESNT IT WORK???

[Bowie69]

I have no cat either.

The pre-cat CO pipe is there for setting the AFM up, originally Audi stuck a hose on it and sampled the gasses at that point.

I wish CO meters were cheaper, what with everything coming from China for pennies, this is one thing that has held the money. I suspect this is the root of my problem though, as it is about the only thing to not have been adjusted as per factory, only by wideband lambda.

The final possible is as suggested above, excessive blowby, but then the engine is on 198K now, so I would probably forgive it that

[steve briance]

I may have made a breakthrough in the 7A bouncing cold idle saga...

I went for a remap yesterday and it was a very very interesting live mapping procedure out on the open road. Wide band lambda plugged into spare boss on exhaust, software showing what is going on with the fuel and the WB lambda screen showing AFR going down the road on varying throttles.

I have the 034 motorsport injectors and the bouncing idle.

EVERYTHING was checked prior to the mapping work as there is no point in working on a car with faults, by everything i mean:

Fuel pressure. 3.5 rising to 4 bar without vacuum.
Fuel flow 2.5 litres returning to tank per minute
Lambda control. value of 1. and reading 10 times every second.old one was only managing 5.
C.O - 0.5%
HC - 95ppm
VAG fault code reader plugged in. no faults.
Coil voltage. 13.4 with engine running
Alternator output. 14.2v
Spark plug operation. consistent across all 5 plugs, coil building spark nicely.
TPS range. no problem. 3.3v at full scale deflection.
MAF responding. (beware not all operating MAFs are equal - some output more voltage than others)
Compression. 14.7 BAR across all 5 cylinders with only 5% max variation.
Cam timing (adjustable pulley installed) spot on all the marks.
Inlet air / vacuum leaks. none.
Exhaust leaks . none,.

Everything reassuringly working.


On cold start with the red 034 injectors the AFR was 10.9:1. WAY rich and the ECU was struggling to manage it. It was tries valiantly to control the idle by opening and closing the idle control valve to get the running into closed loop mode. After a period of bouncing, it always sorted itself out and is always better when hot.

The fueling map was turned down under cold start conditions and lo and behold, it has completely cured the problem. Now the cold mix is 14.5 - 14.7:1 and perfect. A cold start this morning after standing all night and i couldn't believe it - perfect smooth idle. First time ever i think this car has done that in my 17 years ownership!

I shrewdly suspect the issue may be down to over fueling. Hard to check without a WB lambda but it was as plain as day that mine was rich. The only thing you can adjust without the benefit of an ECU emulator is the idle mixture. would be well worth double checking if you currently have issues. Once hot the MOT test is measuring closed loop idle control using the lambda and this isnt reflective of what the ECU is up to when cold as the lambda doesn't do anything for the first few minutes...

A thoroughly good day out and some interesting results but that will be in another thread...