Stuttering and hesitation at large throttle openings

[audiman]

Helps if i read the whole problem!!! Yeah, i second Dougs thoughts on boost leaks. BTDT loads of times.

[4WheelDrifter]

You can never rule out the boost leaks.

[Kodiak]

Thanks for all the good feedback here. Unfortunately, I'm more confused than ever.

Some say it's a fuel problem, but I used Sunoco Ultra 94. Would Optimax be better still, or is this unlikely to be a fuel problem? I guess the next tank of fuel will confirm.

I've searched the forum a lot and there are other people describing my symptoms, I think. Sometimes it's a boost leak, but I don't know how to test for that. Some say it's an MAF problem. I don't even know what that is. Others say it's the overboost protection, but that just shouldn't be, I don't think.

Here's the link to the ECU my car has:

http://www.andersonmotorsport.com/ca...products_id=91

The car is otherwise stock, but for a K&N filter and high flow exhaust. The link above says that the ECU upgrade is designed with North American fuel in mind, and to be totally driveable. So I don't think it's a sketchy ECU.

That leaves:

1) Fuel -- the next tank will show
2) MAF -- what's that?
3) Boost leak -- how to test, and what are the symptoms? are we talking about split hoses, or something much worse, like cracked manifolds?
4) Overboost protection kicking in -- buy why?
5) Something else

Can we, maybe, systematically eliminate some of these problems?

Anyone here in Southern Ontario?

[audiman]

Right then...

BTDT means Been There Done That

A dodgy MAF would make the car almost undriveable, this is the sensor that measures the air going into the enigne, bolted to the air filter box.

If this only happens when booting it hard, or using Wde Open Throttle, then i would suspect a boost leak, normally a hose. This can be tested by buying a pressure test kit from Lee on this forum, they arent dear. Do a search for them. This is what causes overboost protection, it is to save the turbo from killing itself.

[Doug_RS2]

Visually check all hoses for a leak - boost leaks can cause overboost protection.

If you don't see anything take one hose of at a time and check more thouroughly. Or get a bung in the hose at the filter and pressurise the whole lot and listen for air escaping out of a hose.

[Kodiak]

Great stuff. Thanks for that. I will start searching for leaks, and Lee.

The car is certainly not 'undriveable'. It's perfect except when approaching WOT.

So a hose is the most likely culprit, then? And the leak is most likely between the air filter and the turbo?

If I just run the car and have a good look, what are my odds of finding the leak? Decent, or is that a waste of time?

Forgive me if this is a stupid question (but that's why I ask before doing): How 'bout holding a lit cigarette up to the air filter and looking for smoke coming out of the leak?

[audiman]

Nah, there are loads more hose and joints on the car, all the small bore hoses that come off the inlet manifold need to be air tight too!!

You need to pressurise the whole system using Lee's pressure test kit, to about 16 psi and make sure that it doesnt hiss out anywhere.

You wont find it with the car running.

[Doug_RS2]

Most likely a hose - maybe a loose jubilee clip.

Any rubber hose that does not contain water could be the culprit !!

Work your way from airbox - the maf is a plastic tube bolted to that - then a hose from the maf to the turbo - then the turbo to IC, IC to throttle body - probably a few hoses on the way. You also have a few smaller hoses connected to that to check.

[Kodiak]

Most likely a hose - maybe a loose jubilee clip.

Any rubber hose that does not contain water could be the culprit !!

Work your way from airbox - the maf is a plastic tube bolted to that - then a hose from the maf to the turbo - then the turbo to IC, IC to throttle body - probably a few hoses on the way. You also have a few smaller hoses connected to that to check.

Hee hee. "Jubilee clip." We call those "hose clamps." Vive le difference.

Does my car have an intercooler? I've looked but don't see it. Where is it?

Thanks for the tips. I'll do what I can until I get my hands on a pressure test kit.

I hope this isn't heresy, but could an Audi dealership do this for me without gouging me too bad? It sounds simple, and they ought to have the equipment, right? (I know...so naive)

[4WheelDrifter]

Unless Dealerships are very different there, naive.

[audiman]

LMFAO, Audi dealership have the equipment/knowledge!!!! I guess yours are better than ours! It could take a few hours to find the problem. Especially if you have to remove the bumper to gain access to the hoses, like on the S2.

[4WheelDrifter]

IIRC, whatever time it takes an amateur to do, double it for a dealer. They'll probably be surprised when they don't find a V8 under the bonnet!

[Kodiak]

Okay then.

[auditude]

Okay then.

Hi,

Just a thought, I didn't see it mentioned here yet. If you ran the tank very low, it's possible that some sediment and junk that was in the tank got sucked into the pump and is clogging the fuel filter. It might be worthwhile to replace the fuel filter and see if it helps.

Cheers,

Ken

[Mihnea]

Guys, no one mentioned gas in canada and US are (RON+MON)/2 spec, not RON????????


98 RON equals to 93.5 R+M/2, so it's definitely not a fuel quality problem IMHO, unless the pump was selling crap, but Sunoco 94R+M/2 is good stuff usually ;-)

HTH,

mihnea