red turbo rocket

<center><img src="http://pictureposter.audiworld.com/57540/dscf0162.1.jpg"></center><p>I seem to have developed a miss or more like a stumble in my engine. It,s almost like the engine isn't getting enough fuel at low revs. It seems to disappear above 3000RPM but I'm not sure if that's just because the higher RPms are masking the problem. Any ideas?? Maybe a coil problem or an O2 sensor problem? Where should I start? I've done a search and it hasn't really helped.

thanx in advance
Anders

TripleBlackS6

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TripleBlackS6

Ignition Misfire on 1992-96 S4 AAN engine with coil over ignition?
The 1992-96 US made S4's 5 cylinder 20V engine uses individual ignition coils
for each cylinder and two ignition coil modules (Ignition coil drivers). This
system also uses a short ignition wire connector lead between the ignition
coil and the spark plug which normally should have approximately 5000 ohm
resistance when measured across each end with an Digital Multi-Meter (DMM) in
Ohms setting.
One ignition module controls the coils on cylinders 1 and 2, and the other
module controls the ignition coils on cylinders 3, 4, 5. The original Audi
part number for the module is 4A0 905 351A, the Bosch part number is 0 227 100
209. The system uses two of these modules. Several folks have run across
intermittent misfire problems that have been traced to a defective ignition
coils and in some cases to a defective ignition module. Trouble-shooting these
ignition misfires can be tough as it is difficult to locate the one ignition
coil or module that is causing the problem.
The original Audi part number for the ignition coil is 034 905 105, these
coils are manufactured by Beru, the original Beru number shown on the coil is
0 040 100 009. The replacement ignition coil I purchased on Nov. 1, 2001 had
the Beru # 0 040 100 043.
Test Case
I worked on one 1994 S4 recently with an intermittent misfire that only
occurred when the boost level was above ~1.6 bar when the ignition system is
under the most strain. I first tried connecting a known good used ignition
module in place for the module for cylinders 1, 2, but the misfire was still
there. Then I changed the module for cylinders 3, 4 and 5 with the used good
module. This did not affect the misfire either, so I pulled the coil pack from
the top of the engine and disconnected the connectors at the firewall. I
installed a known good coil pack from another S4 and found that the
intermittent misfire was gone. Then I went back to the suspect coil pack and
tested each of the 5 short ignition wire connectors to make sure they each had
approximately 5k ohms of resistance. Each of the 5 ignition coil wire
connector leads tested ok.
Then on the suspect coil pack I tested the resistance from the center of the
coil high voltage output to the metal case of the coil.
When using a Fluke 87 DMM set to the 40 Mega-ohm resistance test range, and
with the Positive lead connected to the center coil output and the DMM common
lead connected to the coil metal case, I saw very high resistance readings.
The DMM showed "OL" which means the measurement is over 40 Mega-ohms and is
too large to correctly display or measure correctly. One of the ignition coils
looked to have been replaced recently on Cylinder #4 which may explain why it
measured only 5.4 Mega-ohms, when all of the other cylinders ignition coils
measured over 40Mega-ohms, and gave the OL reading on the DMM.
The Fluke 87 DMM has a unique range when measuring very high resistance, up to
100,000 Mega-ohms, it is called the conductance range that reads in
Nano-Siemens (nS). One Nano-Siemen is 1 X10-9 Siemens, or 0.0000000009
Siemens. The range for this setting is up to 40nS. You can convert a
Nano-Siemens conductance measurement to its equivalent resistance in ohms, by
dividing 1000 by the nano-Siemens reading.
For example: 2.00 nano-Siemens equals 1000/2.0X10-9 or 500 Mega-Ohms.
I measured across the ignition coil center output using the Fluke 87 DMM in
the regular Mega-ohm resistance range and using the special Conductance range
setting with the common test lead on the coil metal case, and the positive
test lead on the coil High Voltage output center conductor.
AAN Engine Resistance in Ohms Conductance in nano-Siemens (nS) Cylinder 5 OL
(above 40.0M) 16.5nS Cylinder 4 5.4 M OL (above 40.0nS) Cylinder 3 OL 23.85nS
Cylinder 2 OL 0.02nS Cylinder 1 OL 16.80nS
Notice that cylinder #2 ignition coil has a very low conductance reading 0.02
nS, which equates to a very high resistance reading, almost up to 100,000
Mega-Ohms which is near the limit of the DMM.
I suspected that this Cylinder #2 coil was the one causing the intermittent
misfire. Replacing coil #2 fixed the problem, my assumption was correct!
The known good S4 coil pack I used for test purposes had the following
readings when I measured across the ignition coil center output using the
Fluke 87 DMM in the Mega-ohm resistance range and also when in the special
Conductance range setting with the common test lead on the coil metal case,
and the positive test lead on the coil High Voltage output center conductor.
AAN Engine Resistance in Ohms Conductance in nano-Siemens (nS) Cylinder 5
5.05M OL (above 40nS) Cylinder 4 3.84M OL (above 40nS) Cylinder 3 6.60M OL
(above 40nS) Cylinder 2 6.07M OL (above 40nS) Cylinder 1 6.30M OL (above 40nS)

|skolnick

It will also pay for itself in increased gas mileage. See if the symptoms go away after that. If not then look in to coilpacks and POSs.

red turbo rocket

<center><img src="http://pictureposter.audiworld.com/57540/dscf0162.1.jpg"></center><p>I found the POS under the plastic cover on the firewall and disconnected and connected the plugs. This didn't change anything so with the engine idling I pulled off each injector connector one at a time at the fuel rail on the top of the engine. 2,3,4,5 made the engine run rougher but #1 seemed to make no difference. I suspect this means that either the POS for cyl 1 and 2 is bad or I have a bad individual coil for cyl 1. My 2 questions now are: Where is the individual coil for each injector connector and how should I procede from here.
Thanx for all your help and advise. It's really appreciated.

TripleBlackS6

I suggest that you invert the plugs that go into the 2 POS, and check if the problem passes to a different cylinder. If it does, then the prob is the POS, not the coil. If not, test each coil, or coil #1, that you suspect. The coils are under the retangular cover with four hex screws on top of the engine. Be careful not to damage the big O-ring that seals it.