So basically my question is, has anyone ever had misfires that were isolated to specific cylinders that were solved by replacing the ignition transformer?

I'm STILL having misfire issues. New passenger coil less than a year old. Just replaced driver coil with a salvage one from a 2010 which appeared to clear up some of the misfires on that bank but #10 is still missing. Basically now I have misfires reported on 1, 3, 4, and 10 only above about 2/3 throttle. Drives like a dream at lower load, But most of my misfires are on the bank with the new coil.

I just replaced all the spark plugs and insulators and gapped them down (in case the higher boost from the tune was just too much for the gap). Basically the only thing left on my list before I attempt to get the passenger coil warrantied (and buy a brand new one for the driver's side as well) is the voltage transformer. The car has brand new injectors as of maybe 5 months ago (E85 conversion), and did drive fine on the new setup for a month or so, so I don't suspect the fuel type change or an injector issue.

Here's what I'm struggling with and really need to know. Everything I've read about the ignition transformer, and common sense also dictates, that in the event of a problem on the output it shuts down the entire output until the ignition is cycled. That's in fact what happened when my original passenger coil was acting up...the whole bank would go dead so the car would run smoothly but just be down on power. Currently, it's just killing the cylinders that are misfiring which results in a very stumbly/unpleasant driving experience until the car is restarted. This leads me to NOT suspect the voltage transformer unless someone else has experienced the exact same thing and found that to ultimately be the fix.

 

I used to have same problems as you. Misfire on WOT on multiple cylinders. I also have a tune which results in higher boost and more coil pack issues. All I did was change the driver and passenger side coil packs together, along as with brand new bosch iridium spark plugs and spark plug sockets, and everything started to work normally again. No misfires, no problems on WOT, nothing. I did have issues with the voltage transformer before, but that resulted in the whole bank of cylinders 1-6 not receiving power. I do not believe the transformer is related to specific misfires on specific cylinders. When I fixed the transformer, the bank of cylinders started to work normally again. At this point, I recommend getting brand new coil packs and spark plugs, as well as the red rubber spark plug sockets. It is going to be expensive, but you can't really avoid it. These cars are very expensive to maintain. It was 120 grand when it was brand new after all.

 

Have you check the 15amp fuse? From what i have heard, driver side fuse box have a 15amp fuse that can get blow and cause a missfire and it powers coilpacks.. #58.. Mine did missfire 5-7 and change all plugs and wires just because it also need it and a clearing all codes and since then running great.. Still new with the MB world but just doing the research since cant sleep when car is down.. Just my .02cent

 

That's what I am afraid of, but I feel I owe it to FCP to do my due diligence and absolutely eliminate other possible causes before having the coil assembly warrantied. If I go that route, I will be buying the driver's side new as well. Everything I've seen about the ignition transformer indicates that it's all or nothing on a bank when it goes out, not individual cylinders. II also have a very aggressive tune on E85 and upgraded heat exchanger. Attached is what I have for info on the ignition system.

 

^^Just in case that's useful for other searchers.

 

I have not, but I will double-check all the fuses just in case. I have cleared codes many times to see if it's always the same cylinders coming back up and it does appear to be. When it first started it would only act up maybe half the time when I went WOT. Now it's guaranteed to happen any time I'm over about 2/3 throttle.

 

Rent a good voltage transformer for $50 at v12icpack.com

before buying new Coils

 

Yes, I've been talking to Clark about it. He doesn't think it's the transformer either, but it's a cheap enough way to find out for sure that it's probably the route I will go.

 

You can rent two coils from him too , if the transformer isn't the culprit

Given the cost of these parts the rental program is ideal for troubleshooting rather than throwing parts at it

 

Thank you for the suggestion, but the deposits would become a huge issue at that point. That would cost me a total of $2,580 plus shipping to do. Granted, I would get most of it back if I manage not to damage anything in the process, but it's still a huge chunk.

Since 3/4 of my problem is on the year-old coil that's under warranty from FCP, and I know that replacing the other coil with a newer salvage one reduced the number of misfires I was seeing on that bank, I am quite confident it is in fact a coil issue but I just wouldn't feel right warrantying it on a guess so I do feel the need to rent a transformer (as well as verify fuel pressure even though I'm confident it's not a fueling issue).

I'm headed to the shop now to see what the fuel pressure looks like while it's acting up. If that is stable/checks out, the plan is to rent the transformer just to verify that's not a problem. If it isn't, I will have eliminated: plugs, insulators, compression, injectors, fuel pump/pressure issues, and voltage transformer, leaving only the coil at which point I'm comfortable requesting that FCP replace it, as well as biting the bullet on a second brand new coil from them for the other side (assuming they do in fact honor their fantastic warranty...I have yet to try it).

 

In that case, it is definitely the coil pack. I think you should save your time and money and just get the coil pack. It definitely isn't the transformer since both your coil packs are still receiving power. I'm telling you this based off my own experiences with coil pack-related misfires and transformer-related misfires.

 

Fuel pressure is fine. It spikes momentarily when the computer kills the injectors when the misfire starts up but it definitely isn't dropping off/fuel starvation.