following other issues...3k stu..........mble

[fesuvious]

Hello!

So, its been a busy couple of weeks and I haven't worked on her, therefore the ignition problem that I might have is probably still there. BUT. theres something else.....

The '3k stumble', it seems more like a '3k pause...pause...pause, wait, aaaannnnnnnddddddd boost' Now I know it wasn't like it before and it seems to have coincided with the slight (intermittent) that I mentioned on here a couple of weeks ago. The misfire that is random and irrespective of revs and unaffected by boost or not.

Any clues?

I am hoping to tap the wealth of knowledge on here prior to getting 'stuck in' this afternoon and tomorrow.

Suggestions, hints very gratefully received.

[Sabine]

Hi,

Rectifying the infamous 3k stumble may be quite a bit of a task ...

Here is what you should watch out for and check:

- I suspect that spark plugs, ignition leads, fuel filter, fuel quality (no old fuel) are 100% perfect, right ?

- the original ECU software has quite a noticable 3k stumble ... this is normal and can only get minimized with the later enhanced S4s code (BTW, the original 3k stumble mainly is created by a lean running condition especially around that 3k RPM range)

If everything is perfectly fine with your engine setup it will be still noticable, but if some or more parametres are not spot on, the 3k stumble will get worse and worse ...

- check if your minimum air rate screw is set correctly (Freescan should show around 35-40 IAC counts when the engine is warm and idling correctly around 1000 rpm)

- check your wastegate mechanical minimum boost setting. The correct setting is 0.65 - 0.70 bar. A bit on the higher side towards 0.7 bar wont hurt )

- check your fuel pressure. A clogged fuel filter or a lazy fuel pressure regulator can do many wired things ... Just have a look at your integrator values with Freescan. This will tell you if you are on the high or low pressure side (= if the integrator is higher than 128 than it tells you that the ECU is constantly adding fuel ... hence maybe low fuel pressure ...)

Yours

Sabine