I am new to this forum and try to do my own vehicles maintenance. Our ‘97 A8 started running rough after tanking up while on vacation. Suspecting crap in the gas that perhaps is clogging an injector, I put in a bottle of fuel dryer and fuel injector cleaner and made it home. It seemed like it was running on 7 cyls.

The next day it ran worse. I connected up the Vag-Com and pulled the codes. See below. Of these codes, I decided to start with the ECM.

18020 - Engine Control Module Incorrectly Coded P1612 - 35-10 - - Intermittent. This seemed like a likely candidate. I pulled the ECM coding with Vag-Com and it indicated -01273. Checking this by searching online came up with the same code for USA / Quattro / Automatic Trans so this must not be the problem . But why did I get this code? Seems odd.

18010 - Power Supply Terminal 30, P1602 - 35-10 - Voltage too Low – Intermittent. I had replaced the battery since it was going dead just leaving the car with the ignition in the Acc position for troubleshooting half an hour at a time so I was not too worried about this fault.

I then decided to look into the multiple misfires on cylinders 2,3,5,8. I decided to see of the ignition coils could be the culprit. I swapped the coils from cylinder bank 1,2,3,4 with the coils on 5,6,7,8. The misfiring stayed on cyl 2,3,5,8 so the coils are not the problem. It would seem unlikely that 4 would fail at the same time anyway.

Next I decided to see if the fuel injectors were the culprit. Since it is harder to swap the injectors, I decided to see if the injectors were getting the signal from the ECM so I put a noid light on each of the cylinders 2,3,5,8 and it lit OK on each one so I was getting signal to the injectors. I know this is a real general indicator but it helped me rule out the ECM having flatly failed. That indicated that it must be the fuel injectors. I replaced the fuel injectors since I was still running the originals with 213k miles on them and had in the recent past run into injectors sticking. I cleared the DTC’s and fired it up and it seemed to run just fine for a few seconds and then started running rough and the CEL came on. I pulled the codes and the same cylinders 2,3,5,8 were misfiring. The fact that the engine started to run normally and then started misfiring makes me wonder if the ECM is shutting down cylinders 2,3,5,8 to protect the engine from potentially dumping raw fuel thru these cylinders.

I then noticed the firing order cast into the cylinder head: 1,5,4,8,6,3,7,2. My misfiring cylinders are every other cylinder in the firing order! This seems too ordered to be random misfiring. Could there be some function in the ECM that is causing this?

I then decided to take a look at the ECM since I had read that a number of people with random misfires were due to moisture either in the ECU or the injector harness connection to it. I opened the waterproof box under the hood at the passenger side firewall and everything seemed nice and dry. No surprise since we have had an exceptionally dry summer. I did not attempt to open the ECM or disconnect any connectors here since I have not messed with an ECM before but I can’t rule the ECM out.

Checking online for the possible causes for P0300 Random/Multiple misfires lists:
1) Air Intake System leaking – a possibility
2) Fuel Supply faulty –have put in a new Fuel pump at 150k miles.
3) Injector(s) faulty – they are brand new
4) Ignition Cable(s) and/or Spark Plug(s) faulty – The connector that connects the coils to the plugs were swapped with the coils so these are ruled out. The spark plugs are a possibility. They were replaced at 150k mi.
5) Ignition Coil(s) faulty – have ruled these out
6) Exhaust Gas Recirculation (EGR) Valve (N18) stuck/open - a possibility
7) Camshaft Position Sensor (G40) faulty – a possibility
So the likely candidates seem to be:
• Air Intake System leaking
• Spark Plug(s) faulty
• Exhaust Gas Recirculation (EGR) Valve (N18) stuck/open
• Camshaft Position Sensor (G40) faulty
• Possibly ECM.
Any recommendations on what to look for on each of these or any other thoughts?

Saturday,23,July,2016,13:19:55:63583
VCDS - - windows based VAG/VAS emulator running on windows 7 x64
VCDS Version: 16.8.0.3 (x64)
Data version: 201600803
Ross-Tech: Home

VIN: License Plate:
Mileage: 343520km-213453miles
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
Chassis Type: 4D - Audi A8 D2 (1994 > 2003)
Scan: 25 01 03 08 11 15 16 17 18 35 37 45 55 56 57 65 67 75 76 77
02
Mileage: 343520km-213453miles
-------------------------------------------------------------------------------
Address 01: Engine Labels: Redir Fail!
Part No: 4D0 907 557 D
Component: 4.2L V8/4V MOTR AT D05
Coding: 01273
Shop #: WSC 00000
VCID: 2D5B2868E7E96156E5-4A20

12 Faults Found:
18010 - Power Supply Terminal 30
P1602 - 35-10 - Voltage too Low – Intermittent
16684 - Random/Multiple Cylinder Misfire Detected
P0300 - 35-00 –
16689 - Cylinder 5
P0305 - 35-00 - Misfire Detected
16692 - Cylinder 8
P0308 - 35-00 - Misfire Detected
16687 - Cylinder 3
P0303 - 35-00 - Misfire Detected
16686 - Cylinder 2
P0302 - 35-00 - Misfire Detected
18020 - Engine Control Module Incorrectly Coded
P1612 - 35-10 - - Intermittent
16684 - Random/Multiple Cylinder Misfire Detected
P0300 - 35-10 - - Intermittent
16689 - Cylinder 5
P0305 - 35-10 - Misfire Detected - Intermittent
16692 - Cylinder 8
P0308 - 35-10 - Misfire Detected - Intermittent
16687 - Cylinder 3
P0303 - 35-10 - Misfire Detected – Intermittent
16486 - Mass Air Flow Sensor (G70)
P0102 - 35-00 - Signal too Low

 

Oh Lawt.... That's a crap load of issues. First thing I'd check is the grounds for the engine wiring harness. Loosen them a little. Wiggle them around if you can and retighten. Also check the ground straps from the engine block to the body. Pour grounding can cause a boatload of head scratching. Eliminate that first before throwing any parts at it.

 

Ignition Power Output Stages; there are two of them, each fire 4 coils, when commanded to do so by the ECU. N192 fires 2,3,5,8, and N122 fires the other 4 coils. Swap the connectors on these and see if the misfires move.