200tq problems

[quk@isham-research.demon.co.uk (Phil Payne)]

In message <348F978D.3AD13229@poboxes.com> Gerard writes:

> I don't know if this will help in any way. I have 1990 200T which
> is just called Turbo here in South Africa. When pushing "hard" at
> about 3500 RPM I could feel the nose drop and the motor sag as if
> a power loss was happening. About  a week ago I finally reached over
> and checked the vacuum line coming out of the wastegate as it has
> always had a bit  of cloth braiding missing. The pipe felt soft so
> I replaced it with a piece of rubber fuel line hosing made by
> Goodyear and also saw the old line was badly fraid at the wastegate
> end. Since then I haven't had the hesitation at 3500 RPM. So perhaps
> check the vacuum line on the wastegate.

Just attach a boost gauge and do the prescribed test run.  That'll find if 
there's a boost problem or not.  It's more likely for such things to be 
associated with the WOT switch.
 
With this combined WOT switch being as troublesome and finicky as it is, I'm 
surprised there aren't any better diagnostics.  It seems that static continuity 
testing (continuity tester across switch and open throttle by hand) is utterly 
inadequate as a final arbiter of function.  Even switches that look good in 
daylight seem to go intermittent at speed on a revving engine, and low 
resistance seems more important than simple continuity - say below 4 ohms.
 
So far, the best diagnostic tool I have seen is a little harness made up by 
Scott Mockry.  This fits between the wastegate frequency valve and its 
connector, with a long lead taking a LED into the cabin.  You just tape it 
in front of the driver.  It's simple - with the MAC12D (and MAC11/MAC13) the 
ECU takes over wastegate control at WOT. So if you hammer the foot down, the 
LED should flash.  So far, this tool has proven infallible, and it has found 
one WOT switch that tested OK in daylight to be defective in a moving car.

(For those following the story - we plan displacement vs. voltage measurements
 on an MB air mass sensor for this afternoon, and we may even be able to make
 the first runs to measure plate displacement under load on both a stock
 engine and one with some air path modifications.)

-- 
 Phil Payne
 Committee Member, UK Audi [ur-]quattro Owners Club