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Old 20th June 2010, 12:30 AM
A8D2driver A8D2driver is offline
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Unhappy Ignition amplifier on pre-facelift 2.8L

Hi. Can you tell me where the ignition amplifier can be found on a pre-facelift 2.8 A8. The car has started to tick over abnormally (lumpy rather than surging) and with a misfire detectable when driving at 1000 rpm, particularly up slight inclines (under load). The misfire is not detectable at higher speeds. Also time to start the engine when turning over with the starter motor is now slightly prolonged, although the engine always does start. New spark plugs haven't helped. I would suspect the amplifier rather than the coil pack just from general reliability issues reported on VAG ignition systems using this set up. Thanks for any info on this

Last edited by A8D2driver; 20th June 2010 at 11:40 PM. Reason: too long
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Old 20th June 2010, 10:51 AM
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Conan_the_Librarian Conan_the_Librarian is offline
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Its underneath the coilpack at the front of the engine after the covers have come off. It's part of the coil.
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Currently,
2000 S8, Merlin Purple, Leather Pack 1, Winter Pack 1, SPAX adjustable suspension, AP Racing 6 pot front caliper, 385mm fully floating disks, EBC Yellow Stuff Pads, Black Diamond grooved rear disks and predetor pads, D2 Doctors Brake Block.
1997 4.2 A8SQ - the Projekt. 12 years and ongoing!
1997 4.2 A8SQ - Ming Blue. Restoration sat waiting; saved from the Scrapyard
2003 C5 Allroad 4.2Q - Cobolt Blue. Towing car. Laid up awaiting manual conversion.
2005 C5 Allroad 2.5TDi FE - Grey - Workhorse.
2015 Q3QS SLine - Daytona Grey. Lots of extras! Long Haired Admirals cutter.

Previously
2003 C5 A6 1.9TDI FWD - Loaner from D2 Doctor Lifex
1997 S8 - Ming Blue. Loaned out and written off. I loved that car. My first engine swap after cambelt failure.
1996 4.2 A8SQ - Ming Blue. 178k on a cambelt! Trader's 8. Delivered to A8Parts at Lifex.
2003 2.8 A8SQ - powder blueish. Fill in for a while. Sold on.
1998 1.8T A4 Avant FWD. Ming Blue (there's a theme here), PEX for the 97 S8.
And a list of non VAG going back 40 years before I saw the light.
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Old 20th June 2010, 11:58 PM
A8D2driver A8D2driver is offline
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Thanks for the information. Cleaning the terminals on both sides of the unit with a fine file and electrical terminal cleaner (ignition amplifier unit part no 4A0 906 351) hasn't improved the irregular tickover and still detectable misfire at 1000 revs when driving. Shows up as noticable very slight jerkiness on the move at low revs 1000-1200 in town, as well as the tickover irregularity when at standstill. Never cuts out or feels as if it will cut out or not pull away. Not detectable at higher revs and pulls away from this rev level very smoothly with no evident reduction in power or torque; cruising on motorway unaffected. I'll try changing the ignition amplifier.
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Old 21st June 2010, 08:26 AM
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Conan_the_Librarian Conan_the_Librarian is offline
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Have you used VagCom on it yet?

I would recommend having it scanned before spending any money as there are a couple of processes that will help pin down the culprit.

VagCom may tell you which cylinders are misfiring. You can then swap the plugs between cylinders and see if the misfire follows the plugs.

Or you can change HT leads and see if the misfire follows the HT leads. If you don't have VagCom, there should be someone in your area that can help.
__________________
Conan (the Librarian)

Watch it if you dare

Currently,
2000 S8, Merlin Purple, Leather Pack 1, Winter Pack 1, SPAX adjustable suspension, AP Racing 6 pot front caliper, 385mm fully floating disks, EBC Yellow Stuff Pads, Black Diamond grooved rear disks and predetor pads, D2 Doctors Brake Block.
1997 4.2 A8SQ - the Projekt. 12 years and ongoing!
1997 4.2 A8SQ - Ming Blue. Restoration sat waiting; saved from the Scrapyard
2003 C5 Allroad 4.2Q - Cobolt Blue. Towing car. Laid up awaiting manual conversion.
2005 C5 Allroad 2.5TDi FE - Grey - Workhorse.
2015 Q3QS SLine - Daytona Grey. Lots of extras! Long Haired Admirals cutter.

Previously
2003 C5 A6 1.9TDI FWD - Loaner from D2 Doctor Lifex
1997 S8 - Ming Blue. Loaned out and written off. I loved that car. My first engine swap after cambelt failure.
1996 4.2 A8SQ - Ming Blue. 178k on a cambelt! Trader's 8. Delivered to A8Parts at Lifex.
2003 2.8 A8SQ - powder blueish. Fill in for a while. Sold on.
1998 1.8T A4 Avant FWD. Ming Blue (there's a theme here), PEX for the 97 S8.
And a list of non VAG going back 40 years before I saw the light.
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audi 2.8 a8v6 fwd 1995, audi s8 2001

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