Hello everyone,
I have 2004 E55 that developed misfiring on one bank, and as I or any of the MB specialist shops the car has visited have been unable to figure out what is wrong, I thought to ask if anyone here could help me figure this out.

Here are the facts...
The car has fixed sc pulley, stock crank pulley, 1050cc (or similar size) injectors, LTH with race cats added later on, upgraded fuel pumps and upgraded cooling. Basically after I installed these mods and got the map from RaceIQ I drove like 4000km with absolutely no issues.

At some point I started to have occasional engine stalls on cold engine if I had to stop and start moving again and the car was on a slight uphill slope. At this point my guess was the torque converter was going bad, so didn't think too much about it at that point. Then short while after the car started misfiring on Bank 1 (passenger side on LHD car). Codes being misfires on cylinders 1, 3 and 4, and also random/multiple misfires.

After that it has visited three different MB specialist shops, who have been unable to fix it, but here is a list of things that have been done by them or me.

• Crankshaft position sensor replaced
• Camshaft position sensor replaced
• Plugs replaced twice
• Plug wires replaced
• Ignition coils replaced
• Multiple gaskets all over the intake which were leaking at least a bit
• Compression tests done
• Fuel pressure checked

Many times after a shop has fixed something, they say the car is working fine, only for it to start misfiring after driving 10 minutes or so. In many cases it felt like to me, that on cold startup it might work just fine for a minute or two, and then it starts misfiring.. Sometimes it starts misfiring immediately after starting the engine. Sometimes when driving it feels like it is running fine on moderate speeds, but on very low speeds its clearly misfiring and on highway speeds the whole car shakes.

I did the compression test and everything was fine on that regard, but the plugs on the misfiring side were very black, especially compared to the other bank. After that I tried to clean them a bit (still very black...) and unplug the o2 sensors in case there is something wrong with them, and it certainly did not make it run better, however it's hard to rule the o2s out since I guess the plugs aren't working anymore as they should. The car was driven max. 500km after replacing the plugs, so there is clearly something wrong causing them to go so black.

So I feel like my issue is (probably) that the plugs stop giving spark, which causes the misfiring, but what could cause them to go in such horrible condition so quickly? I'm trying to figure out all possible variables that would affect all four cylinders on one bank, but none on the other. The previous technician working on the car mentioned that the exhaust manifold is leaking somewhere, which is observable since there is exhaust gasses visible on the passenger side bank when the airfilter box is removed. Could this be the issue? It would seem weird if it is, since they didn't fix it.. But to me it seems like this could cause the o2 sensor to think it's running lean, which then causes it to run very rich and in turn turning the plugs black?

I hope I remembered to write down everything, and any help, suggestion or guesses even are appreciated. Thank you in advance.

 

Yes. Need to monitor fuel trims while this is happening and see if one bank is maxing out.

 

Why do you have such big injectors on such a lightly modded car??

 

I went through something similar recently. Everything electrical checked out. Turned out that the crank pulley had come loose, and threw the engine out of balance. On cold startup, it was OK, but after a few minutes, the CEL was blinking, and I had multiple misfire codes. So, in short, the actual failure manifested itself in fault codes and indications of electrical issues, when in fact it was purely mechanical.

 

Thanks, I will get a new set of working plugs on that side and log those.

I will be installing E85 kit once I get the car running properly, and the guy at the shop I bought my injectors from said that size will be good.

Symptoms sound very familiar indeed, thank you for sharing this, will have to make sure that is properly tightened.

 

So I replaced the plugs from the misfiring side, kept the primary oxygen sensors unplugged, and what do you know, it ran great. I monitored using the data from secondary oxygen sensors and most of the time it was slightly rich on both sides, which I guess should happen since it runs on the map + some extra fuel. But the most important part is that now the readings are similar, so it would seem like the primary o2 sensor on the passanger (right) side was at fault here. I will update this thread again after I have installed new o2 sensors, so if that fixes the issue maybe this helps somebody in the future.

 

I had one O2 sensor rattle loose on me. On top of making a clanking noise that sounded like it was from the rear of the car (it was weird), I had one bank straight on the money, trim wise, and the other side always adding 7-10%. It did not make an exhaust leaking sound, and there were no fumes. Was odd indeed!

 

what was your ltft before and after for both banks?

 

One side was always +1-3% and the other was always 7-14%. The difference always got worse as the ambient air temp went up.