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Audi A4 1.8 BEX Turbo - Surging when accelerating #

Posted by Mark Poulton on November 14, 2012, 12:18 pm

Year of Manufacture *: 2004
Engine Size and Code *: 1.8 BEX

Customer just bought the car on way home oil light came on so he stopped and recovery bought it to us. We found oil pick up pipe blocked so replaced. On starting there was a load rattle from turbo area striped and found main spindle snapped due to lack of oil pressure so replaced with new one.
When road tested car holds back then surges then holds back.
I have no codes have done a smoke test for air leaks Checked fuel pressure. when driving actual boost pressure rises higher than demanded pressure the you see wastegate operate and this is when you get the surging. Any body any ideas

Re: Audi a4 1.8 turbo surging when acclarating

Posted by Chris Angus <iframe src='https://members5.boardhost.com/ukautotalk4/info/user=UKAT5111' width='330' height='300' border=0 style='border:none;'> on November 14, 2012, 1:19 pm, in reply to "Audi a4 1.8 turbo surging when acclarating"

not enough pressure reaching the actuator.
What's the difference between actual and desired?
Can you log with duty cycle to confirm if ecu is trying to correct?

Check

Faulty/ sticking N75 valve
leaking or blocked vac pipes
incorrectly adjusted wastegate

Chris

Re: Audi a4 1.8 turbo surging when acclarating

Posted by Darryl Setchell on November 14, 2012, 3:03 pm, in reply to "Re: Audi a4 1.8 turbo surging when acclarating"
Message modified by board administrator November 15, 2012, 12:56 pm

check the boost pressure control valve i think its located on the bulk head can give the fault you describe

Re: Audi a4 1.8 turbo surging when acclarating

Posted by Matt Booth <iframe src='https://members5.boardhost.com/ukautotalk4/info/user=ukat3028' width='330' height='300' border=0 style='border:none;'> on November 14, 2012, 8:48 pm, in reply to "Re: Audi a4 1.8 turbo surging when acclarating"
Matthew Booth

I've seen exactly this before with recon turbos. The actuator seems to react too slow so you get the over/underboost loop. I've managed to adjust the linkage before to reduce the effect but I've never had this problem when using brand new garrett units.

If you log the boost specified, actual and n75 request you'll probably see te N75 react and then a delay before the pressure actually changes.

May not be the same thing but gives you a possible direction.
Where did you get the turbo from?

Matt

Re: Audi a4 1.8 turbo surging when acclarating

Posted by Mark Poulton <iframe src='https://members5.boardhost.com/ukautotalk4/info/user=ukat3051' width='330' height='300' border=0 style='border:none;'> on November 15, 2012, 2:33 pm, in reply to "Re: Audi a4 1.8 turbo surging when acclarating"
Keith Poulton

Thanks for replying
Chris
Desired 1660 mbar
Actual 1980 mbar
Checked n75 it works and it is sealed to inlet duct until activated we it opens up.
I can't log on to duty cycle

Matt
Turbo came from BTN Turbo through our factors
rang them this morning to ask the settings for the wastgate. He told me it should start moving at .2 bar when checked it started moving at .3 so i have adjusted it. Just taken it up the road its a lot better but still doing it a little so i am just going to adjust it a little more when it cools down and see if it makes it better.

Re: Audi a4 1.8 turbo surging when acclarating

Posted by Matt Booth <iframe src='https://members5.boardhost.com/ukautotalk4/info/user=ukat3028' width='330' height='300' border=0 style='border:none;'> on November 15, 2012, 9:37 pm, in reply to "Re: Audi a4 1.8 turbo surging when acclarating"
Matthew Booth

BTN are usually pretty good. Sounds like you're on the right track.

Matt

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