Mystery3B problem (long)

Mon Dec 20 07:42:16 PST 2010

Mine did exactly that last month.  Got all kinds of odd codes.   It was the 
MAF sensor (no code for the MAF).

Went out to Anderson Motor sports, they plugged in a used one off a 95  S6  
(same part number) and all was fine.  Cleared all codes, none  since.

What made me think it was the MAF was when I unplugged it with the motor  
running, nothing changed.

Pete,
91 Avant

In a message dated 12/20/2010 9:33:00 A.M. Central Standard Time,  
benswann at verizon.net writes:

Brought to you by Ben's Brain Benders and Knuckle  Busters

Here we have another diagnosis and trouble-shooting problem  from hell..

I'm trying to see what I may have missed so far prior to  delving into the 
engine itself.

The car is a '91 200 20V quattro  sedan.  Engine has 198k miles on the 
clock.  The car
was brought  to me in hopes that a brief look and some parts swapping might 
resolve  a
problem that has so far stumped the owner and apparently prior  mechanics.

The engine starts but won't rev., runs rough, and has no  power - enough to 
throttle baby
it around, but basically barely gets out of  its own way.  The boost guage 
never shows
below .7 on stock ECU and  will generally idle at .8 or .9.  I hooked up a 
guage and the
engine  is not pulling much vacuum, perhaps around -8 PSI at idle.

***Here are  some things that were checked prior to me looking at the car - 
many of  which
I've confirmed.  *** My comments *** added to owners original  comments.

[Owner comment - The wastegate diaphragm is  good.

Owner pressure tested the system to about 25psi and it was  holding. Only 
hissing came
from around the dipstick, which now has a new  o-ring. 

Owner changed the ECU with a known working unit that hasn't  been chipped 
and it didn't
make a difference. 

Owner replaced the O2  sensor with a brand new one with the correct part 
number. Again,
no  difference. 

Owner claims timing is correct, there are all new belts,  pulley, 
thermostat, water pump,
valve cover gasket, crankshaft and camshaft  gaskets, valve job, head 
gasket etc. It's
all fresh.  *** This is the  part I am not sure about - see details below 
***

Owner replaced the  distributor rotor with a new one with the correct 
narrow tip. The
gear is a  metal one so no cracked plastic issues there. 

Owner  kept getting  a code for the RPM sensor so replaced that.  No change 
and still
shows  a code. **code has cleared**

Owner thinks the multi temperature sensor  must be bad (or the wiring) 
because the
coolant temp gauge works on and  off. I haven't had a chance to replace it. 

***I explained that MTFS  does not directly effect the engine operating, 
but is for the
temp guage  and coolant reservoir and after-run system***
*** There was a CTS code that  probably was what he was referring to - more 
on that below
***

Owner  comment - I don't remember all the exact codes. There were a lot. I 
recall  RPM
sensor, running rich, overboosting and there were others. I'd check  them 
first. 

Owner comment - The hose going to the bypass valve is new  also and tried 
another known
good valve. None of it made a difference.  

Owner comment - I tried replacing the wastegate frequency valve with  the 
one out of my
'02 S4. It's the same but part numbers are different. For  whatever it's 
worth, there was
no improvement. Could it still be bad? I  don't know.  *** This all looks 
good to me ***

I did the output  test and everything clicked properly. The only thing I 
couldn't get  a
signal from was the carbon canister solenoid. It's behind the head on a  
hose. I replaced
the too and no difference. I checked the power going to  the wires and if I 
recall
correctly there was none. *** Here is where I  found some problems - 
explained below ***

Owner comment - I tested the  throttle position sensor and the harness. It 
all checked
out. I even took  it apart to check for any broken traces. It's all good. 

Owner comment  - I  tested the altitude sensor. I think that's what it's 
called. The  one
that's on the intake manifold, right after the throttle body. That one  
checked out too. 

Owner comment - I was also getting a code for the  sensor that's behind the 
driver side
kick panel. I think it was another  sort of altitude sensor. I'm mixing the 
two I know.
My memory is failing me  right now. Anyways, I replaced that too with no 
signs of
improvement. *** I  clarified that the IAT is on top of the manifold and 
the altitude
sensor is  inside the car -  I followed up with testing and substituting 
known  good
sensor, but no change ***

Owner comment - The MAF I have not  replaced so I have no idea if it's good 
or not. I
think I checked the  connector though and it was good. It seems like 
someone might have
changed  the MAF with a used unit. There's a number written on it like you 
would find  in
a junk yard. So maybe someone tried replacing it, but who knows if it's  
good.  *** I
tried  good MAF(s) - no change (even worse running)  ??? ***

Owner comment  - The Michelin Man hose is good and I also  checked the 
turbo. There is
very minimal play in the shaft. Very normal. No  sign of the blades ever 
hitting the
housing. 

Owner comment  -  I haven't checked the fuel pump, fuel pressure regulator 
or replaced
the  filter. I don't know what condition they are in. The hose going to the 
FPR is  good
and hooked up. *** Fuel pressure test may be in order ***

Owner  comment - My S4 was running well but I did a tune-up on it so the 
spark plugs  I
pulled out of it I put in the 200. I wanted to see if anything changes  but 
there was no
difference. The wires and rotor I haven't replaced so I  don't if they pose 
an issue. 

Owner comment - That's all I can think of  right now. So basically what 
happens is that
the car cannot be revved up  past around 4200rmps. This doesn't matter if 
it's in neutral
or under load.  When the car is under load you can only give it gas very 
gradually (not
the  case in neutral, revs just fine up to a point), anything sudden will 
cause it  to
buck severely. 

Owner comment - If you do rev the car to that  limit (4.2K), and do it for 
a few seconds,
it'll start pouring out black  smoke and you can hear it misfiring VERY 
loudly, like
series of explosions.  During one of these episodes the boost gauge will 
spike all the
way up to  1.9 bar(in neutral) and you can hear the relay inside the ECU  
clicking
constantly. After you let off the gas the car will start running  rough and 
the wastegate
frequency valve clicks away frantically.  ***  this is strange explanation 
of the problem
that I have not confirmed or  witnessed - why would the engine barely make 
vacuum, yet
overboost like  that?***]

Presented with this list and discussion about the car, I  attempted to 
trouble-shoot and
isolate the problem.  Here are excepts  from my notes:
- Obeserve problem as MAP output to display - not  correct?  
.Not pulling sufficient vaccum, 
.Reads 1 Bar when  engine not running (OK)
.7 - .9 Bar at idle - should be around  .3?
.engine revved/load change -> .6-.9 should be .3-.8?
**Suspect  vacuum leak in MAP sensor (vacuum) circuit

Hooked up VAG-COM: There  were several codes at first: (abbreviated 
descriptions)
519 G71 Intake  Manifold Pressure Sensor - No Signal
522 G62 Coolant Temp Sensor - Short to  Ground
516 F60 Throttle Position Sensor (Switch) TPS idle - Open or Short  to B+
528 F96 Barometer/Altitude
513 G28 Speed Sensor - OK, car not  running
1262 N75 (Wastgate Frequency Valve) Open or short to ground
553  G70 MAF low signal/intermittant

- Charged Battery
-Tee'd in Mity-Vac  and Boost Guage and found some apparantly porous line.  
Replaced  2
line sections and tested. Vacuum held at 25PSI for over 2 min - from  
manifold to ECU
connection.
-Restest - still has problem, and no  apparent change.
-Pulled Codes - same as before.  Cleared Codes ->  Persistant or new codes 
appearing now
are:
G62 CTS, N71 Idle Stabilizer  Valve, F96 Alttude sensor.
Cleared codes again - same  appear.

Proceeded to test CTS, wiring and after much wire chasing and  confusion 
found what was
sure to be the problem:  There were 3 sensor  connectors(CTS, EVAP, Heater 
valve) located
near or in back of the  head.  Someone had connected the CTS to the Evap, 
the EVAP to  the
heater and the Heater valve to the CTS.  So I moved the three  sensors 
being out of place
to the correct locations.  Ready to call  owner and proclaim I found the 
problem(s).
Start car - runs as crappy as  ever.  (expletives deleted) - note CTS 
sensor tested  in
spec.

Pulled codes/cleared codes/pulled codes:  Get 528  Barometric/Altitude - 
Open or short to
B+
Tested wiring (OK) swapped in  known good Barometric sensor.  Code cleared. 
 Car still
runs  same.

Swapped out MAF (using AAN and 3B MAFs) - no change or  worse.  Checked 
wires under
connector - looks OK.

Note: Recall  from prior similar engines running like this were due to bad 
MAF or  Bad
Coil.

Swapped Ignition coil - no change.

At this point I  have far exceeded the estimated time to repair this 
problem.   I
discussed possible problems with the owner:
All codes now cleared and  fairly well believe wiring, ECU, sensors to be 
ruled out, even
though there  were several latent problems fixed.  The problem now appears 
to be more  of
a physical problem with the engine.

Some sort of air intake or  induction problem?  Possibly a fuel delivery 
problem.
Suggested  blocked cats - that has already been ruled out accoring to owner 
- exhaust  was
separated from DP and problem existed.

Based on the fact that  the head was pulled and decked/rebuilt and other 
engine work
apparantly  done, I enquired and found problem existed prior to the head 
work.   ?
Possible mis-alignment of exhaust w/resp to intake cam ?

What  (else) could be causing this problem.  Ideas?

Ben

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