Weird MC engine problem

[Perry, Christoper (EDS)]

By "appreciable load" do you mean just revving the engine or actually
driving?

Does the fuel pressure stay good right at the moment it dies?  If the car
has been sitting awhile could it be some "gunk" accumulated in the tank?  It
would float around at Idle but get sucked down and clog at a higher flow
rate possibly.

Another thought, fuel related:  Sticky plunger in the metering head?  Idles
Ok but when you give it throttle it can't compensate with more fuel and
dies? Maybe actuates too slowly, engine dies then gets too much fuel when
you try to restart?

On the electrical side, is the hall sender providing a clean signal? Maybe
as the distributor spins faster the signal is too dirty to provide a good
pulse and the ignition gets confused.  Of course that would (should) show up
when pulling codes.

Alternator not up to snuff?  Battery going bad ie. creating a short under
load?

Of course your, and my, favorite... check the grounds. I know, preaching to
the choir ;^)

Always difficult to work with cars that have been sitting awhile...

HTH,
Chris Perry
89 90q

-----Original Message-----
From: Phil Payne [mailto:quattro at isham-research.com]
Sent: Friday, August 09, 2002 9:57 AM
To: urq at audifans.com; quattro at audifans.com
Subject: Weird MC engine problem


Before I start - this car is a dog.

It's an Audi 200TQ (5000) with an MC engine run by a MAC14.  It was off the
road for an
unspecified period, believed to be long, and then had some kind of
electrical event.
Basically every component on the auxiliary relay panel with a transistor in
it was fried.

So were a few other things - like the central locking pump ...

The ignition switch is also extremely suspect and the tachometer and trip
computer are dead.

Anyway - I've gutted and rebuilt the electrics.  The diagnostics run and the
ECU stores no
codes.  The car will start and idle from cold - duty cycle is 50%ish at
idle, ISV current 440
milliamps.

If you try and put any appreciable load on the car, it dies instantly and
won't restart.  At
this time, an attached code-pulling LED illuminates permanently.  If you
cycle the ignition,
it comes back on with ECU power.

I've swapped the ECU and coil pack for known good ones and tested the
swapped ones in another
car.  Also the control pressure regulator.  The fuel pump has been swapped -
pressures and
flows are within specification.

--
  Phil Payne
  http://www.isham-research.com
  +44 7785 302 803
  +49 173 6242039