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  #1  
Old 3rd May 2019, 04:57 PM
Prefferle Prefferle is offline
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Default S8 D3 truly random misfire

Hi folks,
A truly useful and informative forum.

I have been plagued by a misfire issue that is truly random. One day it’s cylinder 1 and 9 having misfire counts between 9 and 96 with other eight cylinders on 0. Other times these 1 and 9 cylinder will both be at 0 with other cylinders 4 and 6 having misfires with the others all at 0 - very strange indeed!

I’ve since completed the following:
Replaced coil packs and plugs.
Replaced all connector shells on coil packs
Cleaned earthing connections on cylinder heads for coils.
Replaced MAF connector shells
Unplugged MAF’s with engine idling, resulting in erratic idling as it should be.
Carbon cleaned with walnut shell blasting.
Visual inspected inlet manifold for broken plastic flaps - ok.
VCDS scan resulting misfire codes only for engine.

It shouldn’t be compression as the misfire cylinders can change.

Can anyone advise of any other checks I can run?

Should I power off the battery and unplug ECU connectors and check/clean?
Is there an earth connection that can be corroded or something that can cause this?

Thanks guys,
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Last edited by Prefferle; 3rd May 2019 at 05:19 PM.
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  #2  
Old 3rd May 2019, 07:32 PM
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steamship steamship is offline
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Is the battery in good health? Have you checked the vacuum lines for a possible leak? I don't know if VCDS can monitor fuel pressure, but what about a possible clogged fuel filter?
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My DIY jobs - Replaced alarm horn, Replaced Coolant Temp sensor, Updated RNS-D firmware, Installed Reversing Camera and Digital TV, Dashcam Installation, Retrofitted Rear Blinds, Auto-Dimming Rear View Mirror, Chrome Boot Struts

Sold! 2008 S8 D3 5.2 V10 - Engine: BSM, Gearbox:KLW, Colour:LY7F Suzuka Grey Pearl Effect, Interior:Black/Black with Silver/Black valcona leather with carbon atlas inserts, Bang & Olufsen, Heated windscreen, Soft-close doors, TV, DAB, AMI, Quad Zone, Auto Boot, Auto dim Mirrors, Keyless entry, PDC with rearview camera, AFS II Headlights

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Old 4th May 2019, 05:18 AM
Prefferle Prefferle is offline
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Quote:
Originally Posted by steamship View Post
Is the battery in good health? Have you checked the vacuum lines for a possible leak? I don't know if VCDS can monitor fuel pressure, but what about a possible clogged fuel filter?
Thanks steamship,
Battery good - less than a year old and no VCDS codes.
Vacuum lines mostly replaced - i’ll look into these again.
Fuel rail pressure checked on VCDS, so have not replaced fuel filter - I’ll replace.

one thing when I reset all codes with engine at idle - it sounds like the engine smooths out for a few seconds before pulling misfire codes again.

I willl report back with findings.

Thanks.
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Old 4th May 2019, 09:49 AM
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steamship steamship is offline
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Looks like you've covered everything that I can think of.

I just re-read your original post and noticed this line:

Should I power off the battery and unplug ECU connectors and check/clean?


I only recently discovered that the ECUs on the D3 are just lying exposed in the plenum chamber, and now wondering if that area might be the cause, as I'm thinking that since the symptoms are random in nature, maybe water has got into the ECUs, or at least into the connectors.

Since you replaced most of the vacuum lines, and they're probably worse to get at than on a 3.7 D2, I'd opt to investigate the ECU connector first, and at least rule them out before checking the vacuum lines.
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2001 A8 D2 FL 3.7 Q - LPG Conversion, Engine: AKC, Gearbox:FBB, Colour:LY5X Aqua Blue pearl effect, Interior:WJ light beige/dark beige valcona leather with burr walnut inserts

My DIY jobs - Replaced alarm horn, Replaced Coolant Temp sensor, Updated RNS-D firmware, Installed Reversing Camera and Digital TV, Dashcam Installation, Retrofitted Rear Blinds, Auto-Dimming Rear View Mirror, Chrome Boot Struts

Sold! 2008 S8 D3 5.2 V10 - Engine: BSM, Gearbox:KLW, Colour:LY7F Suzuka Grey Pearl Effect, Interior:Black/Black with Silver/Black valcona leather with carbon atlas inserts, Bang & Olufsen, Heated windscreen, Soft-close doors, TV, DAB, AMI, Quad Zone, Auto Boot, Auto dim Mirrors, Keyless entry, PDC with rearview camera, AFS II Headlights

My DIY jobs - Fan Jet Windscreen Washers, Retrofitted Electric Side Blinds
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Old 4th May 2019, 10:19 AM
Prefferle Prefferle is offline
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Thanks Steamship,

I’ll get straight on that. I’m also hoping to find and clean all earth connections I can find.

Regards,
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Present cars
Daily driver: BMW e65 730d
Batmobile: 2006 S8, D3, 4E 5.2L V10 BSM with (loud) Miltek SS exhaust, Carbon Fibre trim, Alcantara headlining, soft close and keyless entry.
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Old 4th May 2019, 04:45 PM
ainarssems ainarssems is offline
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A bit strange and I do not have any experience with D3 S8.

Considering this
Quote:
one thing when I reset all codes with engine at idle - it sounds like the engine smooths out for a few seconds before pulling misfire codes again.
I would say ECU detects a problem and cuts fuel to the problematic cylinders to save cats from unburned fuel going into them and damaging them and that results in more misfires. So I would monitor any odd behaviour after you reset and see if there are any problems/reports of misfire in that time to see if it can pinpoint offending cylinder, if that changes over time that it's got to be fuel supply or air metering issue.
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Old 5th May 2019, 11:59 AM
Prefferle Prefferle is offline
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Update; ok so I’ve disconnected battery and disconnected connectors to both ECU’s, all looked clean inside no signs of corrosion or water ingress. I sprayed these with Deoxit and reconnected.
Disconnected and checked all electrical harness connectors along with cleaning up all earth connections (coilpack earth on cyl heads and inside wheel-arches) that I could access.

Reconnected battery.
Start-up ok engine idles smooth with 0 misfire counts across all cylinders.
Test drive with VCDS still connected. No misfires detected.

So far so good. I’ll do a cold start and longer drive for the readiness tests to be completed.

Thanks again guys, I’ll keep updating.
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Present cars
Daily driver: BMW e65 730d
Batmobile: 2006 S8, D3, 4E 5.2L V10 BSM with (loud) Miltek SS exhaust, Carbon Fibre trim, Alcantara headlining, soft close and keyless entry.
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Old 5th May 2019, 05:03 PM
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Norretal Norretal is offline
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Sounds promising, fingers crossed for you fella

I'd love to hear your S8 with that Miltek fitted, might have a drive down in fact


Quote:
Originally Posted by Prefferle View Post
Update; ok so Iíve disconnected battery and disconnected connectors to both ECUís, all looked clean inside no signs of corrosion or water ingress. I sprayed these with Deoxit and reconnected.
Disconnected and checked all electrical harness connectors along with cleaning up all earth connections (coilpack earth on cyl heads and inside wheel-arches) that I could access.

Reconnected battery.
Start-up ok engine idles smooth with 0 misfire counts across all cylinders.
Test drive with VCDS still connected. No misfires detected.

So far so good. Iíll do a cold start and longer drive for the readiness tests to be completed.

Thanks again guys, Iíll keep updating.
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Audi D3 S8 - 2006 - V10. B&O, Rear blind, 4 zone, Glass sunroof, Through load, Heated rear seats, Digital TV, PDC Advanced with camera, Homelink. (Advanced key, Auto Boot, Extended leather pack 2, alcantara roof, soft close doors, adaptive xenons, Auto dim mirrors, bluetooth and quite a thirst as standard)

Jobs done so far - Inlet manifold gutted , ATE discs and pads all round, front grille, foglight units and foglight grilles, Longlife tailpipes fitted and centre silencers removed, wheels refurbished, fan jet washers, overhauled compressor, 15mm spacers fitted, plus many more...

Jobs to do - keep it on the road

Audi TT - 2015 - Ultra
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  #9  
Old 5th May 2019, 05:59 PM
Prefferle Prefferle is offline
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Thanks Noretail,

You're most welcome to drop in and hear it - it sounds great...

there is some drone during motorway driving that takes some getting used to though...

Regards,
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Present cars
Daily driver: BMW e65 730d
Batmobile: 2006 S8, D3, 4E 5.2L V10 BSM with (loud) Miltek SS exhaust, Carbon Fibre trim, Alcantara headlining, soft close and keyless entry.
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  #10  
Old 5th May 2019, 07:18 PM
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Norretal Norretal is offline
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I had the middle resonators removed on mine and it sounds great, I'm sure the Miltek system exceeds the current sound though
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Audi D3 S8 - 2006 - V10. B&O, Rear blind, 4 zone, Glass sunroof, Through load, Heated rear seats, Digital TV, PDC Advanced with camera, Homelink. (Advanced key, Auto Boot, Extended leather pack 2, alcantara roof, soft close doors, adaptive xenons, Auto dim mirrors, bluetooth and quite a thirst as standard)

Jobs done so far - Inlet manifold gutted , ATE discs and pads all round, front grille, foglight units and foglight grilles, Longlife tailpipes fitted and centre silencers removed, wheels refurbished, fan jet washers, overhauled compressor, 15mm spacers fitted, plus many more...

Jobs to do - keep it on the road

Audi TT - 2015 - Ultra
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