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W221 Mercedes V12 misfire in Cylinder 8 - Ionic Current Signal Drop on Cylinder 8?
I am currently troubleshooting a misfire/smooth running issue on my W221.176 (S600). I’ve pulled the real-time data using Xentry/DAS, and I’m seeing some very specific anomalies in the Ionic Current Signal for the Left Bank (Cylinders 7-12).
While the motor is running at idle (approx 600-625 RPM), most cylinders are reporting within the expected 1.5V to 2.5V range. However, Cylinder 8 is showing a major deviation:
Spark Plug 8a: 4.64 V (Pegged high)
Spark Plug 8b: 0.07 V (Essentially no signal)
I have replaced two used left coil packs and its the same problem with the same cylinder, the spark plugs are brand new and the red rubber insulators are good also! The Right Bank (Cyl 1-6) looks perfectly healthy and balanced.
Does a 0.07V ionic signal always condemn the entire Coil Pack ? Has anyone seen a failing Voltage Transformer (N127) cause a single-cylinder dropout like this, or is that strictly a Coil Pack internal failure? Are there any specific grounding points I should verify for the Left Bank before I order a replacement rail?
I’ve attached the Xentry screenshots for reference. Looking forward to your insights.
why not get either the upgraded or better still aftermarket improved VT from this guy and start there - hoping the coil pack you have is not entirely dead
https://www.v12icpack.com/ lots of posts about v12 ignition failures - total replacement is a 70k mile service necessity
2007 S600, 2007 Chrysler 300 SRT8, 2000 C5 Corvette, 2017 Mustang GT, 2023 300C, and a 2019 Lincoln
Totally agree with BOTUS on the V12 VT and coil pack issues. It sounds to me like a bad VT. I would replace it with Clark's Boost Box. He also sells improved coil packs. I have used his stuff for years. Keep us posted.
why not get either the upgraded or better still aftermarket improved VT from this guy and start there - hoping the coil pack you have is not entirely dead
https://www.v12icpack.com/ lots of posts about v12 ignition failures - total replacement is a 70k mile service necessity
Thanks BOTUS, please correct me if I am wrong. I think the VT just gets DC voltage to to the Coil packs, not specific voltage for each spark plug or cylinder, I have doubts about the cylinder it self or the fuel injectors there
what I read says the cars run a weird set up toggling plug responsibility between a low volt emission clean up spark and next round a high volt big boy ignition spark
I am glad that is only that VT, its very easy to be replaced and tested, will try to get one ASAP, and check the results to see if the voltage comes within range!
I’m new to this, but can you swap the coil packs to see if the fault moves with it?
The ionization feature in the coil packs is iirc a SAAB invention, and it is used to detect knock.
with no knock detection, the engine management will retard everything / go lh mode.
on the 600's coil packs of 12 coils are so expensive the last thing you should do it play musical chairs - its a damaged VT that kills good coil packs - even dealerships fail to know this is the root cause and often spend your money destroying replacement coil packs
sadly the two issues often go hand in hand - a slightly odd/aging stick on one bank sends volt spikes around the system and damages the VT, you replace the coil pack and blow up its replacement - usually as you need a third coil pack with 6k wasted already - something clicks and you do the VT at the same time so the third one survives - happy its like new you rip it up the road - but the stress of sparking at big revs on a boosted pot leads to the other bank's aging coil pack popping another coil stick and you kill your new std Merc VT and the circus continues.....
NOTE never use a Merc VT and never start the car if you have a std Merc VT - get a modified one to protect the system.... and swap out the aging coil packs for refurbed ones - its all made clear in the link in post 2
2007 S600, 2007 Chrysler 300 SRT8, 2000 C5 Corvette, 2017 Mustang GT, 2023 300C, and a 2019 Lincoln
Most of us simply replace the two coil packs and the VT as part of a routine tune up. I bought one of Clark's upgraded VTs which has fuse protection against those power surges. I have also used Clark's upgraded coil packs with good service. And don't forget to change the 24 spark plugs with irridium plugs. And while you are doing all that, check to see if you have a valve cover oil leak into the plug that is misfiring. Ask me how I know. All of this is considered routine maintenance on a V12 TT. And I love mine.
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