V12 ignition failures - diagnosis and fix
Thread Starter
Super Member
Joined: Dec 2015
Posts: 502
Likes: 145
From: Tampa Bay, FL
2014 E350 Wagon, 2009 SL550 no ABC
V12 ignition failures - diagnosis and fix
hi, a while back my V12 started having occasional rough idle and was throwing Cylinder 1 ignition failure errors/check engine light. Resetting was not helping for long, so I took the ignition cassette out and sent it for a rebuild. As it was after I changed the leaking turbo seals (which I described elsewhere) I thought that perhaps I damaged something in ignition along the way.
Surprise - errors kept coming back with a rebuilt cassette. It turned out, due to a faulty Ignition ECU/Voltage Transformer.
So here is a proper procedure for diagnosing V12 ignition problems:
1) Get a working Ignition ECU/Voltage transformer - I borrowed mine from Clark at V12icpack, Mercedes S600 ignition coil pack repair, ECU, misfires V12 engines - Home. Clark is very helpful and knowledgeable.
2) Install the borrowed transformer - it literally takes 4 screws and about 5 minutes (metal box on the top of the engine)
3) If the problem goes away, you know it's the transformer and you saved yourself a major labor and parts costs of step 4)
4) If the problem does not go away, check the connections, grounds, etc, pull out the ignition cassette (or have a mechanic do it), check for deteriorated red insulators/proper contacts and eventually if needed get a replacement cassette ($1500 each at the dealer) or get a used one/rebuild yours. I think the rebuild is the right way to go (Clark rebuilds them as well)
Good luck
Surprise - errors kept coming back with a rebuilt cassette. It turned out, due to a faulty Ignition ECU/Voltage Transformer.
So here is a proper procedure for diagnosing V12 ignition problems:
1) Get a working Ignition ECU/Voltage transformer - I borrowed mine from Clark at V12icpack, Mercedes S600 ignition coil pack repair, ECU, misfires V12 engines - Home. Clark is very helpful and knowledgeable.
2) Install the borrowed transformer - it literally takes 4 screws and about 5 minutes (metal box on the top of the engine)
3) If the problem goes away, you know it's the transformer and you saved yourself a major labor and parts costs of step 4)
4) If the problem does not go away, check the connections, grounds, etc, pull out the ignition cassette (or have a mechanic do it), check for deteriorated red insulators/proper contacts and eventually if needed get a replacement cassette ($1500 each at the dealer) or get a used one/rebuild yours. I think the rebuild is the right way to go (Clark rebuilds them as well)
Good luck
Thread Starter
Super Member
Joined: Dec 2015
Posts: 502
Likes: 145
From: Tampa Bay, FL
2014 E350 Wagon, 2009 SL550 no ABC
Certainly taking the car to a professional mechanic/dealer with the right tools and familiarity with this type of a car is the fastest, simplest and often even the least expensive way. But there are also some of us who enjoy backyard tinkering and our own troubleshooting, learning through our own mistakes (and mistakes of others), sometimes saving the money or sometimes paying twice - it's just part of the game :-)
MBWorld Fanatic!
Joined: Dec 2015
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Acura TL 2008 - Acura MDX 2012
Certainly taking the car to a professional mechanic/dealer with the right tools and familiarity with this type of a car is the fastest, simplest and often even the least expensive way. But there are also some of us who enjoy backyard tinkering and our own troubleshooting, learning through our own mistakes (and mistakes of others), sometimes saving the money or sometimes paying twice - it's just part of the game :-)
I subscribe to your way of thinking.
Newbie
Joined: Feb 2018
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S600 w221
Hello i am a new member here I have a 2007 w221 misfiring under load 4500+rpm new coil packs and plugs Lazer iridium can't remember the number but ruled that out the hard way... misfire p300 p308 codes new cam sensor on that side. Used transformer from v12icpack.com clark is awesome.... seems to misfire more when it's cold below 40 degrees car runs great till heavy acceleration super annoying because this is so fun to drive....oh I also have a pressertech tune...all of these things started happening after the tune...is this my problem have anyone else had problems with pressertech? Could I be missing something? Any suggestions would be greatly appreciated. Thank you
Super Member
Joined: Mar 2010
Posts: 643
Likes: 72
From: London UK
2013 W204 C63 AMG, 2008 W221 S65 AMG
Tunes are known to stress the ignition components more than usual, but are you saying you have new plugs, new ignition coils and new ignition transformer? Also, what plugs do you have, incorrect plug gap will cause this problem too.
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2006 S600
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