Mystery3B problem (long)

[Ben Swann]

The MAF has already been swapped out with known good ones - still slightly suspect
though ( possible flaky wire).
 
Ben

  _____  

From: PeterBergin at aol.com [mailto:PeterBergin at aol.com] 
Sent: Monday, December 20, 2010 10:42 AM
To: benswann at verizon.net; 200q20v at audifans.com
Subject: Re: Mystery3B problem (long)


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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