Hesitation / boost flutter - What am I missing - Help,advice

Post by **GregorFuk** » Sun Jul 05, 2009 10:53 pm

Recently got my RS4 back after having both turbos replaced as well as the clutch. I now have some further running issues.

On the faced of it the car runs fine, the clutch is strong, it idles smoothly and pulls as hard as ever. However when pulling through 2800 to 3000 rpm in 5th or 6th using only light throttle there is a slight hesitation / fluttering sensation from the engine (no obvious missfire). Once through these revs it pulls cleanly again. The sensation is very subtle but it is there and is most prominent when pulling up hill. This only happens on light throttle, if I put my foot to the floor it pulls through the revs cleanly in all gears.

I took it back to the garage and they found a sized DV on the drivers side however having had it replaced things are no better. I've tightened up every jubilee clip I can see and changed the N75 valve but the problem is still there. I have a second DV coming on Tuesday which I will fit to the passenger side however I have a sinking feeling that this will still not solve the issue. The car also had a new MAF around 2 months ago.

I've not done a pressure test because I don't have the kit. I do have access to a friend with VAG COM but have not had a chance to scan the car yet.

So, going on the premise that the second DV doesn't change anything does anybody have any ideas, other than "get it VAG COMed" and "do a pressure test", because I'm all out at the moment.

Any help or suggestions would be gratefully received.

Thanks

Gregor

Post by **musty1** » Mon Jul 06, 2009 9:45 am

Sounds like a boost leak to me you need to pressure test it

Post by **GregorFuk** » Mon Jul 06, 2009 11:52 am

I knew someone would say that :-/

I'll have to get all the kit together for a pressure test and that may take a little time.

I have arranged to get access to VAG-COM. I plan to do a few 6th gear runs up a hill and make some logs. Does anybody have any advice on what I should be logging? Block 115 (Boost requested/ actual), anything else?

Post by **frazered** » Mon Jul 06, 2009 12:01 pm

are you not able to get to someone who can fully pressure test it?

Post by **GregorFuk** » Mon Jul 06, 2009 1:08 pm

The only place I would take it is my normal garage. They are good but have not managed to find the problem. I'm not sure if they can do a pressure test.

Post by **Contigo** » Mon Jul 06, 2009 6:29 pm

Take it to MRC or Unit 20, worth the health check money.

Post by **frazered** » Mon Jul 06, 2009 7:35 pm

you need to look at a different garage if you want to get to the bottom of it

with all due respect it does not sound like you have had a specialist look after the car if you are not sure they can do a pressure test / diagnose the fault

how do you know if they rebuilt the engine and properly balanced the turbos?

i would also challenge the logic of just replacing 1 dv at at time, they are so cheap you might as well do both at the same time.

this could be a boost leak and maybe something to do with fuelling? has the filter been changed ?

Post by **GregorFuk** » Tue Jul 07, 2009 8:42 am

Thanks for your thoughts Frazered. I've never had the fuel filter changed but I can't be 100% if it has been done in the past.

Fitting the new DV (710N) and doing some VAG-COM runs, any final suggestions on what I should log?

Will keep you all posted.

Post by **KiwiRS4** » Tue Jul 07, 2009 10:28 am

Hi Gregor, I've been experiencing similar problems. I had it checked out by MRC yesterday and it turned out to be crap stuck in the fuel regulator. After a few cleans she runs alot smoother. The regulator is pretty easy to get to, remove and clean (sub 5mins). If your unsure where it is hola out and i'll send though a picture.

Post by **GregorFuk** » Tue Jul 07, 2009 1:56 pm

Thanks for the info Kiwi, I'd be interested to know where this is. Have sent you a PM with my email address.

Post by **jimbo1234567** » Tue Jul 07, 2009 9:26 pm

get a pressure testing kit off ebay, theyre cheap enough

Post by **mikeyquattro** » Tue Jul 07, 2009 10:17 pm

jimbo1234567 wrote:get a pressure testing kit off ebay, theyre cheap enough

Surely you'd sell yours now that you have sold your RS

Post by **GregorFuk** » Wed Jul 08, 2009 12:15 am

Okay so the new DV made no difference and a scan brought up no fault codes so here are the graphs from an evening with Vag Com. Thoughts welcome.

First a boost curve from a straight pull through the revs in 4th with my foot to the floor

Now the MAF curve from a 4th gear pull.

Now a series boost curves from light throttle 6th gear pulls from roughly 2000 rpm to over 3000 rpm which is where I'm getting the hesitation.

Any thought on the above date, does it suggest a boost leak?

Cheers

Gregor

RS246.com Forum :: The World's #1 Audi R, S and RS Enthusiast Community

Hesitation / boost flutter - What am I missing - Help,advice

Hesitation / boost flutter - What am I missing - Help,advice

RE: Hesitation / boost flutter - What am I missing - Help,ad

Vag Com Results

Who is online