some technical help pls..

[loftgroover]

Can i few technical comments from those techies amongst you please...

Below is the data from a 1999 S3, i have plotted the required boost against the actual boost and the measured airflow in g/s.

Fistly, there is a small dip in boost at 3900 RPM from there to 5400 it follows the required curve, after that boost is ABOVE the required amount, but the airflow drops at the point that the boost departs from the required boost curve.

I can only assume that the throttle is starting to close at 5400, as this would explain the reduced airflow and the increase in boost.

Any comments greatly appreciated...

By the way, N75 is new as is the DV as is the MAF.

 

[242spot]

Ok since this post We have changed
DV
N75
INJECTORS
SPARK PLUGS
TEMP SENSOR
MAF
FPR

Still having the same problem. Were thinking FUEL must be the problem as the new injectors helped but not completely.
Has anyone had problems with fuel pumps not delivering enough under high boost?
Im gonna change the fuel filter tomorrow.
Any help would be great
thanks

 

[dickys3]

I know you have said that you have replaced the MAF, but could your new one be faulty too? Its not uncommon..

Just a thought..

 

[tommo-turbo]

Sounds like the Turbo Inlet Pipe might be collapsing under load. Mine used to die off around 5,500 rpm until I upgraded to a Forge silicon one. Now it's smooth up to the redline...

Have you seen this video before?

http://www.forgemotorsport.co.uk/intake.mpg

 

[Tallpaul]

What fuel do you use? have you checked CF's for each cylinder?

100% sure that there isn't a boost leak?

Are you running the stock airbox and paper filter? Tried a new filter?

 

[Tallpaul]

in fact, have you checked the hose from the N75 to the turbo? also the TIP connection to the turbo?

 

[dultanur]

at around 175g/s , and thinking the car is chipped (around 1.4 bar?) isn't the mass flow a bit low? mine is around 195 max...

 

[242spot]

Thanks all for the advise, yes i had checked all of the above.
Today i changed the fuel filter...... clutching at straws No result ( Expected )
However i had the day off so i took it to Awsome in Manchester. They ran it up on there dyno monitoring fuel pressure and exhaust gas for mixture.
Sure enough we were right the fuel pressure drops off at peak torque and peak power. Running LEAN! hense all the knock and ignition pull back. Still ran 226 at the wheels though COOL about 265-270 at the fly they reakon. Shoud be in for a bit more with correct fueling!
So it booked in to have a fuel pump (190 pounds ) on wednesday followed by another run on the dyno

So that should be the end of it, will let you guys know
thanks for the advise.
scott
Email me if anyone wants the video of the dyno run. Will take some good pics on Wed.
Will be sure to post the new graphs and dyno result for those that are interested this week

 

[242spot]

Cheers for the vid thats interesting!

 

[dultanur]

i hope nothing got damaged while running lean. glad the problem is solved

 

[242spot]

Yeah should be fine the engine management has been knocking back the boost and ignition pulse width to protect the engine, Car seems to be good like that. The technician said its fine, the leaning is not that bad... i guess im just fussy about these things, i like them to be right!

 

[242spot]

PROBLEM SOLVED
Fuel pump changed, running like a cut cat!
Have all the dyno runs on email
if you want to see them email me scottwells@fastmail.fm