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Surging accelleration - 91 200q
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- Subject: Surging accelleration - 91 200q
- From: "Sargent E. Schutt" <email@example.com>
- Date: Fri, 12 Sep 1997 01:52:24 +0000
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I need some serious collective brainpower here regarding my 91 200q,
although I've been making headway. I now only have a surging
accelleration problem (no more stalling). The only engine mods are a TAP
chip and a K&N.
Problem: The car surges as it accellerates. Dash gauge indicates the
turbo is spooling fine. Roll down the window and you can hear the turbo
surging. It is spooling, but it sounds like there is a volume knob being
cranked up and down - eg the sound gets louder and softer, indicating
boost being blown off.
All vacuum lines appear okay, just replaced one vac hose and the crank
case breather hose. Also replaced recently: turbo-IC hose, plugs
(bo$ch)/wires/cap/rotor. Also checked the turbo cut-off valve - checks
out okay and replacing it with a verifiably working one made no
difference. I replaced the TAP ECU and wastegate spring with stock
counterparts and experienced the same symptoms, but with less power as
expected, so it's not in the ECU.
I electrically disconnected the turbo cut-off switch/wastegate frequency
valve (WGFV) (same thing). When connected the gauge will show 1.9 bar at
full boost, but you can feel and hear boost being blown off prematurely,
from around 1.4 @4k on up. The boost will now go to 2.0 in 2nd/3rd gear
when disconnected, but there is still surging in the accelleration. Audi
tech says its running rich but I got the usual "but its got a chip so I
dunno what that means" disclaimer.
Near the top of the rev band the power comes on better and more
consistently, as though I have overridden the wastegates ability to
relieve itself at such boost levels; this is the case both when WGFV is
connected and disconnected. Better overall with WGFV disconnected. Never
stalls under any circumstance. Mainly it feels like either the timing is
not right or the fuel supply is not right, and subsequently the confused
computer is sending bad info to the WGFV. Whatever is causing the
problem is causing the computer to blow off steam at the wastegate too
early. It will start surging well under 1.9, at ~1.4. This is not right.
I used to see it hold 1.9 through 3rd, occasionally bouncing off 2.0.
So: running rich at idle, surging accelleration that improves when the
WGFV is disconnected. This is an electrical problem, I'm pretty sure.
But what kind?
Fuel pump relay?
Knock sensors going bad in upper ranges, but not bad enough to register
with the computer as being so but timing thrown off none-the-less?
What else? I really need some help on this one. Bought a vac tester
tonight at Pep Boys. Will do more accurate checking tomorrow.
All suggestions sincerely appreciated.
Thanks in advance,
91 200q TAP,
86 5ktq I.A.
P.S. Just retro-fitted the S4/6/V8 style brakes. Waiting for sufficient
break-in for evaluation. No more shaking steering wheel is a good start,
but I'm thinking I'll need carbon pads and slotted rotors for a better