E55 mystery
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Member
Joined: Oct 2013
Posts: 131
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From: NE Phila
E55 AMG
E55 mystery
Hey guys, I picked up this 2005 E55 AMG from an owner who gave up on it—now I see why. Cold start - Smooth. Once RPM drops, though, it shakes and misfires—always Bank 2 (cylinders 5-8).
I’ve replaced coils, plugs, injector wiring, MAF, MAP sensors, resealed the supercharger and throttle body. Vtech tuned it. Compression’s solid, valves inspected, smoke test clean.
Odd part: O2 sensors disconnected = better. Closing the throttle = smoother. It’s lean at idle—my AFR gauge shows about 15-16 instead of 14.7. At higher RPM it’s smoother, and richer afr. I suspect mixture or timing. Anyone seen this M113K weirdness? Help!
I’ve replaced coils, plugs, injector wiring, MAF, MAP sensors, resealed the supercharger and throttle body. Vtech tuned it. Compression’s solid, valves inspected, smoke test clean.
Odd part: O2 sensors disconnected = better. Closing the throttle = smoother. It’s lean at idle—my AFR gauge shows about 15-16 instead of 14.7. At higher RPM it’s smoother, and richer afr. I suspect mixture or timing. Anyone seen this M113K weirdness? Help!
Last edited by danil_karmiev; Feb 24, 2026 at 10:06 PM.
Out Of Control!!
Joined: Apr 2019
Posts: 11,962
Likes: 6,802
From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
ALMOST GREAT M113k
Hey guys, I picked up this 2005 E55 AMG from an owner who gave up on it—now I see why. Cold start - Smooth. Once RPM drops, though, it shakes and misfires—always Bank 2 (cylinders 5-8).
I’ve replaced coils, plugs, injector wiring, MAF, MAP sensors, resealed the supercharger and throttle body. Vetch tuned it. Compression’s solid, valves inspected, smoke test clean.
Odd part: O2 sensors disconnected = better. Closing the throttle = smoother. It’s lean at idle—my AFR gauge shows about 15-16 instead of 14.7. At higher RPM it’s smoother, and richer afr. I suspect mixture or timing. Anyone seen this M113K weirdness? Help!
I’ve replaced coils, plugs, injector wiring, MAF, MAP sensors, resealed the supercharger and throttle body. Vetch tuned it. Compression’s solid, valves inspected, smoke test clean.
Odd part: O2 sensors disconnected = better. Closing the throttle = smoother. It’s lean at idle—my AFR gauge shows about 15-16 instead of 14.7. At higher RPM it’s smoother, and richer afr. I suspect mixture or timing. Anyone seen this M113K weirdness? Help!
Now your engine is 99% in great shape.
The story reads like this: your M113K runs well while in open loop. In closed loop it is forced off the rail.
- What s your fuel rail pressure?
- Scrutinize your upstream sensors!
- How old are they ?
- What live numbers ?
- How much new Bosch ?
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Joined: Jan 2014
Posts: 3,967
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From: Republic of Texas
'99 and '05 E55 AMG
Not timing. CPS sensor is hard mounted in the bell housing. If you suspect the CPS is intermittent, replace it. PITA, but doable. Yet this would not result in cylinders 5-8 misfiring, it would result in all cylinders misfiring.
Fuel rail pressure could be a suspect.
When coolant temperature is low the Motor Electronics add additional fuel to aid cold start/idle. The extra fuel is removed when coolant comes up to temp. That is where you indicate the AFR goes lean. So, verify fuel pressure with a gauge taped to the windshield if necessary. 5.1 Bar pressure regulator on the filter/regulator; usually see in the area of 5.3 Bar on the fuel rail.
When you pulled the supercharger, I assume you replaced the injector o-rings? Unlikely but something in the realm of possibility are air leaks around the injectors.
I am not familiar with Vetch. Have you reinstalled the stock programming? Personally, I don't think it will matter as the misfire is on cylinders 5-8 versus all yet I would place it in the basket for consideration.
Have you tried swapping O2 sensors side-to-side and see if the issue follows the O2 sensors?
From your description, I lean towards fuel pressure or O2 sensors or a combination of both. Fuel pressure is easy; O2 sensors can be a female dog so go for good ones. Genuine Bosch or Denso.
Be advised counterfeit products can be mixed in with Internet sellers so purchase from a trustworthy supplier. I once tried to save a few bucks and it bit me in the posterior when I ended up with a set of counterfeit spark plugs...my car made it a whole 23,000 miles while the spark plug gaps opened from 0.028" to ~0.060"...with an E55, don't skimp.
Let us know what your solution is.
Fuel rail pressure could be a suspect.
When coolant temperature is low the Motor Electronics add additional fuel to aid cold start/idle. The extra fuel is removed when coolant comes up to temp. That is where you indicate the AFR goes lean. So, verify fuel pressure with a gauge taped to the windshield if necessary. 5.1 Bar pressure regulator on the filter/regulator; usually see in the area of 5.3 Bar on the fuel rail.
When you pulled the supercharger, I assume you replaced the injector o-rings? Unlikely but something in the realm of possibility are air leaks around the injectors.
I am not familiar with Vetch. Have you reinstalled the stock programming? Personally, I don't think it will matter as the misfire is on cylinders 5-8 versus all yet I would place it in the basket for consideration.
Have you tried swapping O2 sensors side-to-side and see if the issue follows the O2 sensors?
From your description, I lean towards fuel pressure or O2 sensors or a combination of both. Fuel pressure is easy; O2 sensors can be a female dog so go for good ones. Genuine Bosch or Denso.
Be advised counterfeit products can be mixed in with Internet sellers so purchase from a trustworthy supplier. I once tried to save a few bucks and it bit me in the posterior when I ended up with a set of counterfeit spark plugs...my car made it a whole 23,000 miles while the spark plug gaps opened from 0.028" to ~0.060"...with an E55, don't skimp.
Let us know what your solution is.
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Joined: Mar 2008
Posts: 39
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E550
Change the O2 sensors. Fact that it runs well cold - before the O2 sensors kick in - point to the sensors. I had a similar (maddening) "one bank miss" that was cured by replacing the O2 sensors...and no diagnostic tools (including STAR) picked up the bad sensors. Agree with the Denso sensor comment, just make sure you get the Denso with the right connector. Good luck. Let us know how it turns out.
Out Of Control!!
Joined: Apr 2019
Posts: 11,962
Likes: 6,802
From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
CROSSING THE T'S
- good fuel rail pressure
- new upstream O2 sensors
- new ignition (coil+plugs)
- clean MAF/MAP
- good compressions
Now what's interesting is "closing throttle helps"...
This LEAN perhaps from significant "unaccounted air" bypassing MAF ??
Then let's check on possible vacuum leak nearest to Bk2.
You did smoke testing already...
Passed all right!
> What Gives...?
It's not fuel
It's not ignition
It acts like small air leak
-- Something specific to "Bk2 air" is overlooked.
-- This is significant enough to misfire your base fuel trim.
-- Nearly all right!
The PCV system has a clean air inlet with a large one-way check valve... is it failed and blowing back crankcase pressure into the plenum??
Spray carb cleaner carefully around Bk2 on cold engine to help locate leak source... (keep a fire extinguisher handy).
Last edited by CaliBenzDriver; Feb 25, 2026 at 03:13 PM.
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Out Of Control!!
Joined: Apr 2019
Posts: 11,962
Likes: 6,802
From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
from post #7
Now what's interesting is "closing throttle helps"...
This LEAN perhaps from significant "unaccounted air" bypassing MAF ??
Then let's check on possible vacuum leak nearest to Bk2.
You did smoke testing already...
Passed all right!
> What Gives...?
It's not fuel
It's not ignition
It acts like small air leak
-- Something specific to "Bk2 air" is overlooked.
-- This is significant enough to misfire your base fuel trim.
-- Nearly all right!
The PCV system has a clean air inlet with a large one-way check valve... is it failed and blowing back crankcase pressure into the plenum??
Spray carb cleaner carefully around Bk2 on cold engine to help locate leak source... (keep a fire extinguisher handy).
This LEAN perhaps from significant "unaccounted air" bypassing MAF ??
Then let's check on possible vacuum leak nearest to Bk2.
You did smoke testing already...
Passed all right!
> What Gives...?
It's not fuel
It's not ignition
It acts like small air leak
-- Something specific to "Bk2 air" is overlooked.
-- This is significant enough to misfire your base fuel trim.
-- Nearly all right!
The PCV system has a clean air inlet with a large one-way check valve... is it failed and blowing back crankcase pressure into the plenum??
Spray carb cleaner carefully around Bk2 on cold engine to help locate leak source... (keep a fire extinguisher handy).
Thread Starter
Member
Joined: Oct 2013
Posts: 131
Likes: 6
From: NE Phila
E55 AMG
Now what's interesting is "closing throttle helps"...
This LEAN perhaps from significant "unaccounted air" bypassing MAF ??
Then let's check on possible vacuum leak nearest to Bk2.
You did smoke testing already...
Passed all right!
> What Gives...?
It's not fuel
It's not ignition
It acts like small air leak
-- Something specific to "Bk2 air" is overlooked.
-- This is significant enough to misfire your base fuel trim.
-- Nearly all right!
The PCV system has a clean air inlet with a large one-way check valve... is it failed and blowing back crankcase pressure into the plenum??
Spray carb cleaner carefully around Bk2 on cold engine to help locate leak source... (keep a fire extinguisher handy).
This LEAN perhaps from significant "unaccounted air" bypassing MAF ??
Then let's check on possible vacuum leak nearest to Bk2.
You did smoke testing already...
Passed all right!
> What Gives...?
It's not fuel
It's not ignition
It acts like small air leak
-- Something specific to "Bk2 air" is overlooked.
-- This is significant enough to misfire your base fuel trim.
-- Nearly all right!
The PCV system has a clean air inlet with a large one-way check valve... is it failed and blowing back crankcase pressure into the plenum??
Spray carb cleaner carefully around Bk2 on cold engine to help locate leak source... (keep a fire extinguisher handy).
thank you.
same thoughts here
Thread Starter
Member
Joined: Oct 2013
Posts: 131
Likes: 6
From: NE Phila
E55 AMG
MBWorld Fanatic!
Joined: Sep 2007
Posts: 1,481
Likes: 310
95 SL600
> So far you have :
Now what's interesting is "closing throttle helps"...
This LEAN perhaps from significant "unaccounted air" bypassing MAF ??
Then let's check on possible vacuum leak nearest to Bk2.
You did smoke testing already...
Passed all right!
> What Gives...?
It's not fuel
It's not ignition
It acts like small air leak
-- Something specific to "Bk2 air" is overlooked.
-- This is significant enough to misfire your base fuel trim.
-- Nearly all right!
The PCV system has a clean air inlet with a large one-way check valve... is it failed and blowing back crankcase pressure into the plenum??
Spray carb cleaner carefully around Bk2 on cold engine to help locate leak source... (keep a fire extinguisher handy).
- good fuel rail pressure
- new upstream O2 sensors
- new ignition (coil+plugs)
- clean MAF/MAP
- good compressions
Now what's interesting is "closing throttle helps"...
This LEAN perhaps from significant "unaccounted air" bypassing MAF ??
Then let's check on possible vacuum leak nearest to Bk2.
You did smoke testing already...
Passed all right!
> What Gives...?
It's not fuel
It's not ignition
It acts like small air leak
-- Something specific to "Bk2 air" is overlooked.
-- This is significant enough to misfire your base fuel trim.
-- Nearly all right!
The PCV system has a clean air inlet with a large one-way check valve... is it failed and blowing back crankcase pressure into the plenum??
Spray carb cleaner carefully around Bk2 on cold engine to help locate leak source... (keep a fire extinguisher handy).
Out Of Control!!
Joined: Apr 2019
Posts: 11,962
Likes: 6,802
From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
> FUEL/IGN... trims!
What are the LTFT Bk1 / Bk2 ?
What does that mean here ... ??
can one of the new coil/boit/plug/connector may actually be marginal calling a lean trim.
Last edited by CaliBenzDriver; Feb 26, 2026 at 03:00 PM.
MBWorld Fanatic!
Joined: Feb 2012
Posts: 2,626
Likes: 1,216
From: Phoenix
222 S-65
OP reset adaptations. Light it up. Watch O2 sensors come online. Compare 1-4 with 5-8. Swap upstream O2 sensors between banks. Same after doing so? The O2 sensor is ruled out.
Pull spark plugs. How do they read? All lean for 5-8 where 1-4 look normal?
Watch adaptations. What is % of difference side to side?
The fuel is in a fuel rail. Pressure will be the same for all cylinders; esp at idle.
What do you have for misfire counts? An O2 sensor doesn't know a misfire from being lean if the charge doesn't light off in the exhaust manifold.
Pull spark plugs. How do they read? All lean for 5-8 where 1-4 look normal?
Watch adaptations. What is % of difference side to side?
The fuel is in a fuel rail. Pressure will be the same for all cylinders; esp at idle.
What do you have for misfire counts? An O2 sensor doesn't know a misfire from being lean if the charge doesn't light off in the exhaust manifold.
Thread Starter
Member
Joined: Oct 2013
Posts: 131
Likes: 6
From: NE Phila
E55 AMG
OP reset adaptations. Light it up. Watch O2 sensors come online. Compare 1-4 with 5-8. Swap upstream O2 sensors between banks. Same after doing so? The O2 sensor is ruled out.
Pull spark plugs. How do they read? All lean for 5-8 where 1-4 look normal?
Watch adaptations. What is % of difference side to side?
The fuel is in a fuel rail. Pressure will be the same for all cylinders; esp at idle.
What do you have for misfire counts? An O2 sensor doesn't know a misfire from being lean if the charge doesn't light off in the exhaust manifold.
Pull spark plugs. How do they read? All lean for 5-8 where 1-4 look normal?
Watch adaptations. What is % of difference side to side?
The fuel is in a fuel rail. Pressure will be the same for all cylinders; esp at idle.
What do you have for misfire counts? An O2 sensor doesn't know a misfire from being lean if the charge doesn't light off in the exhaust manifold.
Misfires are only on cylinders 5–8. 1–4 stay clean. Cylinder 7 is usually the worst one. When RPM goes up a little above idle, the misfires calm down.
Injection time is different side to side. Left bank is around 2.4 ms and right bank is around 2.7 ms, so it looks like the ECU is adding fuel to the 5–8 side.
Smooth running values are also worse on 5–8 compared to 1–4.
So right now all I know is the issue is definitely isolated to bank 2 and the ECU seems to think that side is lean.
It’s winter here so I can’t really tear into the car yet, but when weather allows I’ll start checking for possible air leaks on that side.
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Posts: 2,626
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From: Phoenix
222 S-65
Rule out leaks with smoke. Keeping in mind with Speed-Density for engine management a vacuum leak will make for the throttle body being more tightly closed at idle than normal.
Swap injectors #7 & #8.
Misfire moves? Buy a set of eight injectors and enjoy smooth running.
Misfire still in #7? Cue scary music.
Unplug electrical connectors to both throttle bodies. Wet with crankcase vapors? They always are. A can of flammable brake cleaner will wash all that ick off. Clean up both throttle plates. Brake cleaner on a rag.
I solved many issues doing so.
Whomever it is who whined about replacing a crank position sensor.... don’t be such a baby. 1/4” drive ratchet, extensions and correct size socket + a new CPS should live in every 211 owners glove box. Only really unpleasant to do with a hot engine. Practice doing it enough to get good at doing it. You’ll be replacing it in the dark with rain.
Swap injectors #7 & #8.
Misfire moves? Buy a set of eight injectors and enjoy smooth running.
Misfire still in #7? Cue scary music.
Unplug electrical connectors to both throttle bodies. Wet with crankcase vapors? They always are. A can of flammable brake cleaner will wash all that ick off. Clean up both throttle plates. Brake cleaner on a rag.
I solved many issues doing so.
Whomever it is who whined about replacing a crank position sensor.... don’t be such a baby. 1/4” drive ratchet, extensions and correct size socket + a new CPS should live in every 211 owners glove box. Only really unpleasant to do with a hot engine. Practice doing it enough to get good at doing it. You’ll be replacing it in the dark with rain.
Last edited by JohnLane; Feb 28, 2026 at 12:18 AM.
Thread Starter
Member
Joined: Oct 2013
Posts: 131
Likes: 6
From: NE Phila
E55 AMG
Rule out leaks with smoke. Keeping in mind with Speed-Density for engine management a vacuum leak will make for the throttle body being more tightly closed at idle than normal.
Swap injectors #7 & #8.
Misfire moves? Buy a set of eight injectors and enjoy smooth running.
Misfire still in #7? Cue scary music.
Unplug electrical connectors to both throttle bodies. Wet with crankcase vapors? They always are. A can of flammable brake cleaner will wash all that ick off. Clean up both throttle plates. Brake cleaner on a rag.
I solved many issues doing so.
Whomever it is who whined about replacing a crank position sensor.... don’t be such a baby. 1/4” drive ratchet, extensions and correct size socket + a new CPS should live in every 211 owners glove box. Only really unpleasant to do with a hot engine. Practice doing it enough to get good at doing it. You’ll be replacing it in the dark with rain.
Swap injectors #7 & #8.
Misfire moves? Buy a set of eight injectors and enjoy smooth running.
Misfire still in #7? Cue scary music.
Unplug electrical connectors to both throttle bodies. Wet with crankcase vapors? They always are. A can of flammable brake cleaner will wash all that ick off. Clean up both throttle plates. Brake cleaner on a rag.
I solved many issues doing so.
Whomever it is who whined about replacing a crank position sensor.... don’t be such a baby. 1/4” drive ratchet, extensions and correct size socket + a new CPS should live in every 211 owners glove box. Only really unpleasant to do with a hot engine. Practice doing it enough to get good at doing it. You’ll be replacing it in the dark with rain.
new injectors, why swap ???
both throttle bodies???
cps is new
MBWorld Fanatic!
Joined: Feb 2012
Posts: 2,626
Likes: 1,216
From: Phoenix
222 S-65
Swap injectors to see if misfire moves. If it does you have a dead injector. All injectors are the same age. One fails; we don’t want to play whack a mole with injectors annually. Injectors are also able to fail to ‘firehose’ Such that the engine ends up hydro-locked. That can make for a bent connecting rod. Or worse.
Two throttle bodies. One regulates power... the other is superdupercharger bypass.
Report back with findings.
Two throttle bodies. One regulates power... the other is superdupercharger bypass.
Report back with findings.
Junior Member
Joined: Mar 2008
Posts: 39
Likes: 11
E550
As someone who had the same problem, and after doing (most) everything you have done, remember....there are few systems that affect only one bank. The MAIN one is the O2 sensors. I would suggest you get TWO new sensors (upstream and downstream - yes, BOTH) and replace them in the bank you are having issues with. I had similar issues with ONLY 5 and 6.... and why would the O2 sensor ONLY affect those two cylinders (who know?). I tell you...I had the IDENTICAL symptoms. I spent weeks looking for the cause. I even replaced the injectors (all 8). BTW, I assume you have the stock exhaust system. If you have headers, it's a different ballgame.
Thread Starter
Member
Joined: Oct 2013
Posts: 131
Likes: 6
From: NE Phila
E55 AMG
Swap injectors to see if misfire moves. If it does you have a dead injector. All injectors are the same age. One fails; we don’t want to play whack a mole with injectors annually. Injectors are also able to fail to ‘firehose’ Such that the engine ends up hydro-locked. That can make for a bent connecting rod. Or worse.
Two throttle bodies. One regulates power... the other is superdupercharger bypass.
Report back with findings.
Two throttle bodies. One regulates power... the other is superdupercharger bypass.
Report back with findings.
Also, they are new. unplugging the upstream O2 improves how it runs, which makes me think it’s a lean correction issue rather than mechanical injector failure. Smoke test didn’t show anything obvious, so I’m looking into something that would affect the entire bank.
Last edited by danil_karmiev; Feb 28, 2026 at 09:29 AM.
Thread Starter
Member
Joined: Oct 2013
Posts: 131
Likes: 6
From: NE Phila
E55 AMG
As someone who had the same problem, and after doing (most) everything you have done, remember....there are few systems that affect only one bank. The MAIN one is the O2 sensors. I would suggest you get TWO new sensors (upstream and downstream - yes, BOTH) and replace them in the bank you are having issues with. I had similar issues with ONLY 5 and 6.... and why would the O2 sensor ONLY affect those two cylinders (who know?). I tell you...I had the IDENTICAL symptoms. I spent weeks looking for the cause. I even replaced the injectors (all 8). BTW, I assume you have the stock exhaust system. If you have headers, it's a different ballgame.
MBWorld Fanatic!
Joined: Feb 2012
Posts: 2,626
Likes: 1,216
From: Phoenix
222 S-65
OP what brand of spark plugs?
I have encountered counterfeit NGK plugs. Didn’t pay real close attention when replacing plugs. Had an intermittent rough idle after replacement that never set a check engine light (V-12 cars need something really wrong to set a misfire check engine light). Pulled all plugs and looked at them closely... sure enough plugs that are supposed to be iridium on center electrode and on ground side... some lack iridium in one spot, some on both. Look closely at plugs whilst comparing with information found on the web and yup! A decades long source of parts (obviously) unknowingly sold me eight (two boxes) of counterfeit NGK plugs. Another thing to watch for.
I have encountered counterfeit NGK plugs. Didn’t pay real close attention when replacing plugs. Had an intermittent rough idle after replacement that never set a check engine light (V-12 cars need something really wrong to set a misfire check engine light). Pulled all plugs and looked at them closely... sure enough plugs that are supposed to be iridium on center electrode and on ground side... some lack iridium in one spot, some on both. Look closely at plugs whilst comparing with information found on the web and yup! A decades long source of parts (obviously) unknowingly sold me eight (two boxes) of counterfeit NGK plugs. Another thing to watch for.
Junior Member
Joined: Mar 2008
Posts: 39
Likes: 11
E550
Hi. The reason that it smooths out is that in the absence of an oxygen sensor, the ECU makes some assumptions and gives you what it thinks is the best air fuel ratio. I don’t mean to be insistent, but that is another clue that the oxygen sensor is the issue. I’ll stop now, but having gone through the identical issue and researching I would really look at the oxygen sensor.
