90 200tq 10v - Total loss of electrical power and bucking

Ben Swann benswann at verizon.net
Sun Nov 22 11:30:23 PST 2009


Regarding loss of power - If there is absolutly no power to anything, even before
turning the key, then go to the source - the battery located under rear seat and check,
clean terminals and ground strap connection to the chassis.  I'll often wire in a second
ground point  and strap  for redundancy, sinc this a the single point of failure to the

Also, you have positive connections at the starter and alternator.  There is a single
point of failure ground strap that goes from chassis to engine - located on drivers side
engine mounting.  Add second strap on the other side fro redundancy - starter bolt to
chassis is a good location.

Several models incl. type 44 have a welded wire connection in harness in certain
locations, but I wouldn't go there unless all else is ruled out.

If the battery went dead due to lost charge, then you may have a bad voltage regulator
or exciter wire disconnected.  I bet you find all sort of wiring that need cleaning up
when you go through things.


If the "buck" is rather dramatic, you may well be hitting the overboost fuel pump cutout
- several chips are programmed to cutout at 1.95 bar, but you may not see that since
often  the digital readout responds far to slow to register before it happens. We can
assume ti is a 1.8 bar chip, as stock would have cutout at 1.5 bar and you would have
seen maybe 1.3 bar at the time of cutout.

Cutout usually is due to a bad lower wastegate hose.  They get porous and look ok, but
come apart when removing  - just replace it if you haven't.  Wastegate diaphragms can
leak, but usually not the problem.  Any of these culprits tend to creep in and get
progressively worse until repaired.

It could be other things - either ignition or fuel related.  Rule out ignition - plugs,
wires, cap and rotor  - usually can get by for diagnosis by cleaning up cap and rotor
contacts with emory file  or even better if you have a dremel tool use a small fine wire
wheel to clean contacts as I bet they are covered with green/white oxide.  Replace lugs
as a matter of course if needed.  Sometimes you can readily tell a wire is bad by
observing engine in pitch dark - amazing the fireworks set off by bad wires.  They can
be tested - 1k ohm for plug wires and 4 k ohm for center wire ( hope I got this right  -
ref. Bentley.  If ignition is still suspect, coil assembly can go bad.

You may have a clogged fuel filter, but not the first thing to replace.  Injectors can
get sloppy, but usually associated with poor low RPM and idle.

Vacuum leaks - sometimes can be major - check, replace and repair lines as needed.


This answer will be put into the online Frequently Asked Questions section of my

[Date: Sun, 22 Nov 2009 11:42:30 -0600
From: "Brian K. Ullrich" <bullrich at ullrichsys.com>
Subject: 90 200tq 10v - Total loss of electrical power
To: <quattro at audifans.com>, "'v8audi'" <v8 at audifans.com>,	"'200q20V
	mailing list'" <200q20v at audifans.com>
Message-ID: <73A7D7194FDC4EF9A162C5A5E95C36D2 at nick>
Content-Type: text/plain;	charset="us-ascii"

Hey guys 

Update on my '90 200tq project. I got everything back together underside and the car is
tight. Runs well, but has a weird buck at 1.7bar. Also, seems to idle a little rough and
probably rich as it failed an emissions test this morning. All that is minor right now.

The REAL head-scratcher is that on the way back from the inspection station, I stopped
at a convenience store, and when I came back out, there was no electrical power in the
car at all. Turned the key; nothing. No accessory power, no lights, nada. It is like
there is no battery in the car.

So, the car is stuck at the store, my shop manuals are behind locked doors at the
wrench's shop, and I'm stumped. Any ideas?]

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