slight running problem?
Turbo Mini Forums

Just got my head on and freshly rebuilt carb fitted, but Having a slight running problem, in first and 2nd gear when I come onto boost it kind of judders and doesn't go like it should, however in 3rd it boosts up fine and goes fairly well, I know my timing needs looking at, would this be causing the juddering in 1st and 2nd, how come it runs fine in 3rd, I have not tried it in 4th yet.

I cannot remember 100%, but I think my afr gauge was saying lean, would this cause it? I am running a bca needle, what is the next richer needle up?

Cheers

Audi s4 b5 - 470bhp & 486ft lbs

On 30th Apr, 2012 Brett said:
yeah stick the bit in and give it a wobble

benny any misfires under boost IF everthing checks out ok ie ignition plugs etc timing is ok you need to fix these FIRST!

missfires under boost are caused by a lean mixture! you AFG will tell you whats happening too lean and missfire

i would search for the T peice trick on here wrote by our very out Turbo dave and pipe that up first, then! ignition and the fueling. you need a BDD Turbo needle as a basic start! you may well be lucky and get the correct mixture by using the screw on the carb ?
before getting the car set up on the rolling road

do the above and please take notice one step at a time benny
i hope this helps,

EDIT:- the head you have fitted will demand alot of air on full boost thats why your AFR is lean
remember lean mixtures under boost cause engine misfires trust your AEM lambda gauge that tells the whole picture ............................ please set the ignition timing @ 6deg before TDC 1000rpm vac pipe to dizzy disconected for the timing and reconect when timed ........... each! notch on the timing cover is 4 degrees the large tooth is top dead centre

and as tom says

Edited by BENROSS on 17th Mar, 2011.

This doesn't sound good, before you mess with timing get the fuelling right first, if you have a wideband then this is easier, however remember when it is misfiring it will be chucking unburned fuel into the exhaust so the lambda will read false RICH due to the unburned fuel.

Thanks lads, car is not being driven until this is sorted, and I am in no real rush. I've got half a day off work tomorrow so will try to get hold of a timing light.

I tried the BDD needle, was at around 8psi boost and it went off the gauge at 17:1+, so tried to BCA and seemed slightly better.

I've tried the mix screw, pretty much from all the way in, which wouldn't start, turning it out until it drove, any richer on the screw and it won't rev up, just bogs down, ill have another go tomorrow see how it goes

Audi s4 b5 - 470bhp & 486ft lbs

On 30th Apr, 2012 Brett said:
yeah stick the bit in and give it a wobble

employ the T PEICE Trick FIRST! as you may have that problem!!!
have a search! benny

Yes will do steve, will have a search when I get on laptop.

Cheers

Audi s4 b5 - 470bhp & 486ft lbs

On 30th Apr, 2012 Brett said:
yeah stick the bit in and give it a wobble

right, just had a read, saved it into favorites. will try the t piece trick tomorrow

Audi s4 b5 - 470bhp & 486ft lbs

On 30th Apr, 2012 Brett said:
yeah stick the bit in and give it a wobble

Part throttle lean off pipe connected? (Yawn) lol

Fuel pressure set to 3.5psi? And rising with boost?

In the 13's at last!.. Just

Part throttle lean off is blocked off, not checked fuel pressure yet, going to try the t piece trick after work see if that changes anything.

Audi s4 b5 - 470bhp & 486ft lbs

On 30th Apr, 2012 Brett said:
yeah stick the bit in and give it a wobble

If I richen it up anymore on the mixture screw it just bogs as soon as I apply any revs, and when I pull the choke out surely the revs should increase? Well mine just stay the same, fueling seems on on cruise and light acceleration, a steady 13-14, but as soon and I give it the beans it goes ok for a second then doesn't want to accelerate, but in 3rd it goes fine, it was still doing it with bleed valve closed at 4psi or so, with bdd and bca needle?

Audi s4 b5 - 470bhp & 486ft lbs

On 30th Apr, 2012 Brett said:
yeah stick the bit in and give it a wobble

little update with more detail... running bca needle, bleed valve closed running only a couple of psi, was also running the 't peice trick'

1st gear, drives fine until boost where it kind of goes for a split second then its asif it cuts out for a split second then goes for a split second and then it backfired, so let of straight away. fueling flicks from 10-15:1, i presume when the fueling flicked to 10:1, this is what you was talking about tom? chucking unburnt fuel into the exhaust?

2nd gear, same as above.

3rd gear, same as above but only for a second then cleared up and boosted fine at around 11:1

havnt tried 4th gear yet.

so im presuming i need a righer needle? any ideas what to try? also read most of you guys run std. BDD needles, but i do not have the knowledge to do this myself.

Audi s4 b5 - 470bhp & 486ft lbs

On 30th Apr, 2012 Brett said:
yeah stick the bit in and give it a wobble

another little update, did some research/reading up on here on profiling needles using the following guide..
http://www.turbominis.co.uk/forums/index.php?p=vt&tid=159683

so off i went and grabbed my BDD needle, must say its not as scary as i thought. only did a little bit at a time, but got it running much much better at 4psi, afr was about 14:1, so still lean but at least im making progress :) going to keep doing it until i get my afr down to about 11-12:1 then gradually turn boost up and re profile when needed

am i going about it the right way?

cheers.

Edited by bennyy on 19th Mar, 2011.

Audi s4 b5 - 470bhp & 486ft lbs

On 30th Apr, 2012 Brett said:
yeah stick the bit in and give it a wobble

sounds like a good plan

Audi s4 b5 - 470bhp & 486ft lbs

On 30th Apr, 2012 Brett said:
yeah stick the bit in and give it a wobble