S4 Slight hesitation at 3200 rpm

[imported_cononcars]

Hi folks,

My S4 has a slight hesitation when charging throughthe gears at around 3200 rpm, more noticeable in 3rd and 4th gears. It pulls like a train until 3200 and then it's as if someone is lightly pressing the brake pedal, the after 3250 rpm, it's pulling strong again.

My S4 has an APR stage 1 and has always had a slight hesitation at this engine speed, but it is getting noticeably worse.

Initial thoughts are a leaking diaphragm on one or both dump valves (standard), but I haven't checked yet. Thought I'd run it past the forum to see if anyone else has had similar symptoms?

Any advice, most appreciated.

Gaz.

 

[dummi]

thats just the switching between the turbos Gaz, the first one cuts off at just about that point and the second one starts up just after, absolutely normal means both your turbo are still doing their job /ubbthreads/images/graemlins/laugh.gif

cheers

 

[imported_cononcars]

Excuse my ignorance, but I thought both turbo's spooled up at the same time.
It is recommended that both turbo's be replaced at the same time if one fails, to maintain synchronous flow from each, to each bank of the vee. This wouldn't be necessary if they were different sizes and / or produced their boost pressure at different engine speeds.

Am I not correct in this assumption???

Gaz

 

[foolish3uk]

they work identically!!!

sounds like your air mass meter

 

[dummi]

you can not equally push the same air into both banks, the turbos if working in sync would push into the same inlet surely.
besides you cann not get a single or pair of syncronised turbos to cover the whole rev range, take for example subaru sti kicks in at 4000rpm for max use of power in the revrange, the 1.8t turbo kicks in at 1800rpm to 5000rpm then dead to the red line.
you can ofcourse syncronise the turbos to run at the same time for more power , like some do with supras
thats how we can get power from under 2000rpm thru to redline in the 2.7t, correct me if i'm wrong anybody

 

[dummi]

my bad then
looks like i have the same problem sorry Gaz

 

[imported_cononcars]

I thought about the AMM, but if that was on it's way out, why would the hesitation be at the exact same rev range every time?

 

[dummi]

not sure there is another thread on this, seems a lot of people have this problem, those with chipped cars on the other thread seem to be able to solve the problem by reverting to the original program saved in memory.

sorry about that thought it would be like the rx7 that blew what turned out to be low end turbo , was a dog at low end then superman at the high end

 

[imported_cononcars]

dummi,

You're correct, both Turbo's feed a common inlet which then splits the flow to each bank. Ignore my comment about supplying each vee. Having 2 small turbo's allows early spool up (low inertia) and also provides enough pressurised air for the top end.
The Scooby has one big mo fo turbo which boots your backside at 4k, and can hold boost at high revs, but suffers terrible lag.

 

[dummi]

right yeah the sti is a bitch to get going i just don't driving that at all.

 

[JamesA3]

I also have this problem on my A3 1.8T and it only happens in 1st & 2nd, its been like it for months and I don't know what to do about it. Also has a lumpy idle

 

[Markey]

What about the waste gate sticking, that can cause a slight twitch in power where it not opening smoothly

 

[DamoS3Q]

My S3 does the hesitation thing at 3000 rpm too, happend after it was chipped up..


Ive changed the dumpvalve and still does it

d

 

[GregC]

I had a surging power delivery when the turbo spooled up on my A4 1.8 T Quattro. Changing the N75 valve seems to have cured it - don't know if this helps....


Greg

 

[S3quatt]

This is a common problem it seems, as i used to have an S4.

Jim at star informed me that it is due to a timing shift at that rpm.(same as VVTI on the jap cars)

it only really shows on the re-mapped motors & shows on the graph.

By the way both turbos do spool up at the same time, it just has 2 small ones to kill the lag.

Otherwise its not a problem.

Hope this sets ur mind at ease.