--PartBoundary Thu Sep 14 12:21:33  11252355
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doin' the fuel injection lamabada.....

If you are refering to the "lambda" unit, sometimes called the oxygen 
sensor, one can test the sensor while installed on the car, but disconnected 
from the computer.  Once warmed up, the sensor shoud "put out" about 
1.0v---if the mixture is stoichiometric, i.e., 14:1, or whatever is "stoich" 
for your local alitude, temp conditions.  warmed up means the sensor element 
is warm enough to react with the passing oxygen molecules....engine up to 
temp. exhaust nice and hot...or, if you have a three wire sensor (2 of the 
wires are heater wires....to quickly warm the sensor...) perhaps as short as 
30 seconds after cold start.

The sensor passes information in the form of voltage, which varies (I forget 
which direction) as the mixture gets richer and leaner.  The computer 
"looks" for the voltage to "be" 1.0v, and uses the result delivered by the 
lambda (oxygen) sensor to adjust the injector dwell time 
accordingly....voila! feedback control.

If you  are reffering to the "computer", this is much a worse situation, as 
far as diagnosis and repair goes.  Computers are full of (or are centrally 
controlled by) semi-conducter devices that make GRAET fuses....they will 
blow much earlier then any other circuit protection device in your vehicle.  
So:  DO NOT introduce any sort of voltage or current (including the 
volts/amps injected into a ciircuit by a low-impedence volt meter!) into the 
fuel injection harness unless you REALLY know what you are doing.  This 
makes testing the fuction (Thevinin equivalent??) of a fuel injection 
computer very difficult.  If not impossible.  Most procedures contain the 
delightful langauge "replace with known good unit...)  I hat it when they 
say that....

It is important to diagnose the root cause of a computer failure.  I ahve 
read of cases where the computer failure was caused byu a "sneak path" to 
grounf, through the computer....from the starter.  L>ots of amps, would have 
blown the computer again, and soon.  Such diagnosis si difficult, and I 
can't think of a Sure Fire WQay to do so.....just gotta look around, make 
sure the grounds are good....and pray.

There are Bosch licensed shops (rebuilds, repairs, etc...) that I have heard 
of, but I've never found one that could service what I was working 
on.....for whatever reason, that information just wasn't out to the 
aftermarket when I needed it.  Hav'nt had the opportunity to get to that 
point on the Westoie, tho.....

always disconnect or connect anything associated with the Fuel Injection 
system while the key is off...and removed.  Disconnect the FI computer 
before arc welding on the vehicle....avoid stray currents, etc.

bowmanr%em@mhs.elan.af.mil
Live Smart.  Think for yourself.  Transform the future.
Original text: (21 lines follow)
>From vanagon@SC-NGM1{MHS:vanagon@lenti.med.umn.edu}, on 9/14/95 10:25 AM:
To: vanagon@SC-NGM1 (Multiple recipients 
oflist){MHS:vanagon@lenti.med.umn.edu}

Has anyone found a cheap way to test the fuel injection lambada to see if 
it is dead or not? And if you just replace it, what are the chances that 
the new (used) one will just fry from the same cause that fried the old 
one (since we don't  know what killed it, eh?) -- we assume it is dead, 
since  the various units activate if you apply current to them with a 
jumper, but not when running the car. This is on an Audi,  but the 
injection systems are pretty much the same.

-- 
Harmon Seaver
hseaver@nyx.cs.du.edu
seaverh@vaxa.cis.uwosh.edu
hseaver@csd.uwm.edu

    All is impermanent, but this too shall pass away, and the way of the
Samurai is death --- so speak your mind now, or forever hold your peace!

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