Suspect coil failure

[Donnie]

Hi,
So.... wife took the a8 today (first mistake?) and when she returned it there was a noticeable misfire. The cat light is on and otherwise runs alright.
I suspect a failed coil - unburned mix then causing the lambda to go out of limit flagging the cat light.
I have vcds and will scan the car tomorrow.
Anybody know different or seen before?
1997 ABZ 4.2.

DM

[ulfilias]

Scan for which cylinder the missfire is on. Swap the coilpack with another cylinder and scan again. If it moves, new coilpack.

[Dezzy]

^ +1 if it doesn't move could be the plug breaking down.

[ulfilias]

The other way to check which one if you don't have a scantool/vagcom/vcds is to sequentially pull the coil pack conector off and place back on while the engine is running, you'll hear a change in sound if that cylinder is doing anything and no difference otherwise. Quite a useful diagnostic trick....If you have the tools it also confirms the connections to the packs.

[Donnie]

ok .. so..

Misfire on cyl 3 diagnosed by vagcom and confirmed by pulling injector connectors sequentially.

Removed coilpack #3 and replaced with #1. Misfire continues on cyl#3 - again confirmed by injector clip.

Removed plug#3 and replaced with #1 - misfire continues cyl#3

I've ruled out coilpacks and plugs.

Here is the VCDS log prior to me starting:

Wednesday,30,October,2013,16:57:26:54668
VCDS Version: Release 11.11.6
Data version: 20121223


Chassis Type: 4D - Audi A8 D2
Scan: 25 01 03 08 11 15 16 17 18 35 37 45 55 56 57 65 67 75 76 77
02

Mileage: 306910km/190705miles
-------------------------------------------------------------------------------
Address 25: Immobilizer Labels: 4A0-953-234.lbl
Part No: 4A0 953 234
Component: IMMO AUZ9Z0B0291186 D77
Coding: 00000
Shop #: WSC 00214
VCID: DFC326F75DE890E0F91

1 Fault Found:
01176 - Key
07-10 - Signal too Low - Intermittent

-------------------------------------------------------------------------------
Address 01: Engine Labels: Redir Fail!
Part No: 4D0 907 557 J
Component: 4,2L V8/4V MOTR AT D01
Coding: 04263
Shop #: WSC 00214
VCID: 336B1A4701E0E480ED9

6 Faults Found:
17978 - Engine Start Blocked by Immobilizer
P1570 - 35-10 - - Intermittent
16500 - Engine Coolant Temp. Sensor (G62)
P0116 - 35-10 - Implausible Signal - Intermittent
00561 - Mixture Adaptation
15-10 - Adaptation Limit (Add) Not Reached - Intermittent
01088 - Mixture Control Adaptation 2
15-10 - Adaptation Limit (Add) Not Reached - Intermittent
16684 - Random/Multiple Cylinder Misfire Detected
P0300 - 35-00 -
16687 - Cylinder 3
P0303 - 35-00 - Misfire Detected
Readiness: N/A

-------------------------------------------------------------------------------
Address 03: ABS Brakes Labels: 4D0-907-379-ABS.lbl
Part No: 4D0 907 379 L
Component: ABS/EDS BOSCH 5 7680
Shop #: BB 37680
VCID: 37732E57159808A0D11

1 Fault Found:
00526 - Brake Light Switch-F
27-10 - Implausible Signal - Intermittent

-------------------------------------------------------------------------------
Address 08: Auto HVAC Labels: Redir Fail!
Part No: 4D0 820 043 A
Component: D2-KLIMAVOLLAUTOMAT_D02
Coding: 00081
Shop #: WSC 23146
VCID: 1A35D7E3864A35C8CEF

No fault code found.

-------------------------------------------------------------------------------
Address 15: Airbags Labels: 8A0-959-655.lbl
Part No: 8A0 959 655 K
Component: Airbag V AUDI D00
Coding: 01022
Shop #: WSC 02314
VCID: 3B7B326729B02CC0359

No fault code found.

-------------------------------------------------------------------------------
Address 17: Instruments Labels: 4D0-919-033-MYW.lbl
Part No: 4D0 919 035 C
Component: D2-KOMBIINSTRUMENT__D16
Coding: 00483
Shop #: WSC 00001
VCID: 264DF313C23281287A7

No fault code found.

-------------------------------------------------------------------------------
Address 02: Auto Trans Labels: None
Part No: 4D0 927 156 E
Component: AG4 GETRIEBE 018 D27
Coding: 00000
Shop #: WSC 00000
VCID: 2B5B0227D9D0BC40A59

1 Fault Found:
00526 - Brake Light Switch-F
03-00 - No Signal

End ---------------------------------------------------------------------

The 16500 g62 coolant seems spurious as once cleared did not return.

00561 - Mixture Adaptation
15-10 - Adaptation Limit (Add) Not Reached - Intermittent
01088 - Mixture Control Adaptation 2
15-10 - Adaptation Limit (Add) Not Reached - Intermittent

These two are a symptom of the missing cylinder I believe.

16684 - Random/Multiple Cylinder Misfire Detected
P0300 - 35-00 -
16687 - Cylinder 3
P0303 - 35-00 - Misfire Detected

I don't see evidence of any random misfire - every time I cleared codes these two came back.
The only exception was when disconnecting the injector these two were replaced with:
1 Fault Found:
17611 - Fuel Injector for Cylinder 3 (N32)
P1203 - 35-00 - Electrical Malfunction

Tomorrow I will continue by checking the injector and best to do a compression check to rule out any mechanical issue.

[Donnie]

Also where are the amplifiers / power stages located?
On the 20v turbo 5cyl cars they are on the bulkhead. I will swap them round and see if the miss stays put.

[PsYcHe]

The amplifiers are on each side on the front face of the block near the top.

[Donnie]

Nice one.

[ainarssems]

Originally Posted by PsYcHe

The amplifiers are on each side on the front face of the block near the top.

Ignition amps are under plastic cover next to windscreen washer fluid bottle filler.

[PsYcHe]

I must be thinking of something else that's on the front then... Been a while since I had an ABZ.