Hesitation or cut off problem

[valjo]

hi !
i have audi s2 aby with complet rs2 upgrade and chip (about 370hp, 1.7-1.8 boos).
last days i have big problem with hesitation and/or cut offs and poor runing. when problem started i hardly noticed small hesitation about 4500rpm, but sun it develop in big hesitation at 3500 rpm. it mostly happend at WOT. when going WOT at cca 4krPm car starts to "cut out" like it would be on rev limiter, but it does not lose boost. sometimes car yust can not go over some rpm (caa 4500) but has constant boost.....
yesterday i managed to hit 1.5 bar but today only 1 bar.......

i have allready make list of things:
-boost leak free
-brand new MAF
-no vag com errors
-DV Forge leak free
-wastegate checked
-n75 tested
-new sparks
-pos and coilpack switched with known good set
-intake temperature sensor checked
-vacuum lines checked

has anyone any idea what should i check next ? Knock sensors ? Poor fuel pump or injectors ?

thanks !!

[prj]

Does your intake (after MAF) hold steady 1.5 BAR?
I know you said you do not have a boost leak, but have you actually used a compressor to pressurize it to 1.5-2 bar?

[valjo]

hi!

thanks for answering !
yes i used compressor and pressurize it up to 2.0 bar. i am 100% sure it is absolut leak free!
yesterday we wnt for drive with vagcom, and we got some quite strange outputs ...
intake temperature wont go higher then 22c..... i guess it is not ok? i diconnect connector and it gave default value 40c but car ran even wors....
ignition timing is at idle about 8 but then goes up to 33, but when i floored car and when it starts to hesitate it drops rapidly to 13 degress... is it ok ?
lambda factor is close to 1, or little over it.. i guess it is ok ?

Does your intake (after MAF) hold steady 1.5 BAR?
I know you said you do not have a boost leak, but have you actually used a compressor to pressurize it to 1.5-2 bar?

[prj]

Lambda is not important.
How did you pressurize your intake exactly?
Did you pressurize the MAF-Turbo rubber hose as well?

If you have a leak between the turbo and the MAF, you will run lean. This in turn will cause detonation, and the ECU will retard timing and remove some boost.

[valjo]

I put plug instead of LMM and block oil brather. It is leak free.
is ignition time ok ?

[S2central.net]

Unmetered air will make you run lean - that means air being drawn in by engine that is not measured by MAF.

Poor running can also be caused by faulty MAF of course if it gives bad info to the ECU. You renewed the MAF already... But have you RESET the ECU by unplugging it for a minute ?

Check the control pipes at rear of inlet manifold to fuel pressure regulator also - a boost leak here will prevent correct fuel pressure being applied across the injectors.

Please explain exactly how and where you are pressurising the intake system to ascertain you have no air leaks.

[valjo]

i have reseted ECU, i changed MAF some weeks before this problem started.

I blocked oil breather hoses and make pressure test. i put plug instead of MAF and pressured system.
I have all vacum hoses new, included hose from intake mainfold to ECU and pressure regulator, so they are 100% leak free.
what should be lambda values at WOT ? i guess far under 1 ?

Unmetered air will make you run lean - that means air being drawn in by engine that is not measured by MAF.

Poor running can also be caused by faulty MAF of course if it gives bad info to the ECU. You renewed the MAF already... But have you RESET the ECU by unplugging it for a minute ?

Check the control pipes at rear of inlet manifold to fuel pressure regulator also - a boost leak here will prevent correct fuel pressure being applied across the injectors.

Please explain exactly how and where you are pressurising the intake system to ascertain you have no air leaks.

[prj]

It's narrowband lambda output in vag-com.
You can't use it for anything, looking at it is useless!
Why do you block the breather?

Just remove the MAF, instead of it put a plug, as shown here:
http://www.friikartul.ee/albums/albu...tester1low.jpg.

And no, your ignition is not OK, it should advance with rev's. If ECU is cutting ignition and boost, it can probably hear knock.
Make sure you have no loose metallic objects banging against the block in your engine compartment as well!

[valjo]

yes that is same tool as i use to pressurise system. i block oil breather to prevent damage in valve seals.....

are you sure that ignition time should advance at WOT ?
i am planing to change gooth knock sensors this weekend too.

Just remove the MAF, instead of it put a plug, as shown here:
http://www.friikartul.ee/albums/albu...tester1low.jpg.

[prj]

Well, it should not drop to 13 degrees...
I don't think just changing random parts will solve the problem.

[Dingo]

Heres a VAG COM print from mine when running well in 3rd & 4th, the BTDC is up to 25 - 26 deg at the top end,
Hope this helps
PS mine turned out to be a bad conection on the MAF

[S2central.net]

I am perhaps strange, but maybe the only person that doesn't like to pressure test in that way... Forcing air into compressor inlet is not air tight method - maybe on a brand new turbo with perfect seals - means you get bubbling noises as air enters oil ways - and pressure drop while testing. My method -

1 - Remove the hose at the turbo which normally connects to the intercooler. This is where pressurised air is designed to come from !
2 - Bung the hose where it meets throttle body.
3 - Pressurise to as much as you dare - this path should be completely airtight - from turbo hose thru intercooler and pressure pipe. It also pushes air against the TBV/DV which should remain airtight unless you apply vacuum to its control port... which is also a neat way to depressurise the system.

Just me 2 cents

[valjo]

do you have any other idea what should be wrong ?

Well, it should not drop to 13 degrees...
I don't think just changing random parts will solve the problem.

[valjo]

thanks for print !
i have changed maf connector and it should be ok now

Heres a VAG COM print from mine when running well in 3rd & 4th, the BTDC is up to 25 - 26 deg at the top end,
Hope this helps
PS mine turned out to be a bad conection on the MAF

[mcandmar]

I am perhaps strange, but maybe the only person that doesn't like to pressure test in that way... Forcing air into compressor inlet is not air tight method - maybe on a brand new turbo with perfect seals - means you get bubbling noises as air enters oil ways - and pressure drop while testing.

I would tend to agree with you as the inlet hose expands quite a lot with 1bar pressure inside however thats where i found my boost leak, over 1bar pressure the hose started leaking on the turbo inlet. Ok technically thats a vacuum leak not a boost leak but i would never have found it without pressure testing that way.

As you say the the turbo oil seals start to leak over 1bar, you can hear it bubbling away with the oil cap removed. But i would recommend testing that way to be 100% sure. Testing from the turbo outlet to intake i usually use 2.0 bar pressure.