Misfire in cylinder six
Thread Starter
Super Member
Joined: Mar 2012
Posts: 535
Likes: 13
From: Franklin, MA
2006 CLK 350/. 2009 CLK 350/2005 Both White
Misfire in cylinder six
So the other day after changing the spark plugs 10 days ago the cars been running amazing. All of a sudden my son tells me check engine light comes on I’m seeing misfire in cylinder six. So I had a spare coil pack from another issue. I had a long time ago. I installed it. Ran the car for a few minutes. Check engine light came back on again. Same cylinder six. Then just in case I swapped out cylinder six and two. I noticed that after 2000 RPMs, the car was shutter a bit stipulating that a misfire was happening. I continue driving the car anyways now this is the fun part, under 2000 RPMs the car seems fine anything over 2000 RPMs she starts to shutter and then the check engine light comes on. I’m going to AutoZone to get some oil I come out I start the car no check engine light I start to drive the car I go over 2000 RPMs the car is fine again. It seems like it’s coming and going . Now I put it under a heavy load for about 15 minutes driving around the neighborhood and the check engine light has not come on since.
What I’m baffled about is why under 2000 RPMs the car is fine and why is the check engine light coming and going can’t be the coil pack because I swapped it with cylinder two and I also installed a new one good one and cylinder six keeps having an issue until the last episode now it seems fine
My next test is to let the car sit for about two hours started up again and see what happens when I go over 2000 RPMs. But I’m just thinking of what to look for. It’s not the cam sensors because that’s not throwing a code is it possible I have a bad spark plug or a fuel injector. Let me know your thoughts.
What I’m baffled about is why under 2000 RPMs the car is fine and why is the check engine light coming and going can’t be the coil pack because I swapped it with cylinder two and I also installed a new one good one and cylinder six keeps having an issue until the last episode now it seems fine
My next test is to let the car sit for about two hours started up again and see what happens when I go over 2000 RPMs. But I’m just thinking of what to look for. It’s not the cam sensors because that’s not throwing a code is it possible I have a bad spark plug or a fuel injector. Let me know your thoughts.
Thread Starter
Super Member
Joined: Mar 2012
Posts: 535
Likes: 13
From: Franklin, MA
2006 CLK 350/. 2009 CLK 350/2005 Both White
So I want to add to something I just discovered I decided to swap out spark plugs too so I took out spark plug out a cylinder six and put it in number for spark plug. Number four I put into cylinder six no spark plugs looked identical in wear and tear. I mean seriously they’re only about two weeks old. Well I drove the car until the check engine light came on again and now cylinder two is giving me a misfire no longer cylinder six so it Hass to be a spark plug issue.
Now it doesn’t look fouled it looks super clean. I didn’t see any cracks visibly in the porcelain so I don’t know years and years and years of working on cars. I’ve never had anything like this happened to me were a spark plug failed that was fairly new how is it possible?
please pardon any punctuation and spelling errors. I’m using speech to text while driving to the lake.
Now it doesn’t look fouled it looks super clean. I didn’t see any cracks visibly in the porcelain so I don’t know years and years and years of working on cars. I’ve never had anything like this happened to me were a spark plug failed that was fairly new how is it possible?
please pardon any punctuation and spelling errors. I’m using speech to text while driving to the lake.
Member
Joined: Sep 2020
Posts: 91
Likes: 15
From: Arkansas & California
'00 CLK320, '01 ML320 Designo, '01 ML320 Sport; '04 CLK320 Coupe Avantgar; '04 C230 SportCoupe (HB)
Go to an O'Reilly's. They have very good scanners now. Pull all your codes, current and stored. You will have to make a note of each. Post those, please.
Go into the individual readings and check your vacuum both at idle and at 2,000 rpm and while increasing rpms. Under 2000 rpm a small leak may not be sufficient to cause 'stumble'. Record those readings. Remember: with engine off, the vacuum should read atmospheric pressure of 29.92. Reading the MAP without starting is a first step in diagnosing if the sensor is accurate.
BTW: I had this same issue on a 3.2L engine - and it was a vacuum leak at the Brake Booster line at the intake manifold port. And a small exhaust leak. In combo those two were causing the 02 sensors to send wrong values - causing a misfire on only #6. Replaced the o-ring and 2 other parts on the intake port (less than $30 from MBZ dealer).
Let us know about these, please.
Go into the individual readings and check your vacuum both at idle and at 2,000 rpm and while increasing rpms. Under 2000 rpm a small leak may not be sufficient to cause 'stumble'. Record those readings. Remember: with engine off, the vacuum should read atmospheric pressure of 29.92. Reading the MAP without starting is a first step in diagnosing if the sensor is accurate.
BTW: I had this same issue on a 3.2L engine - and it was a vacuum leak at the Brake Booster line at the intake manifold port. And a small exhaust leak. In combo those two were causing the 02 sensors to send wrong values - causing a misfire on only #6. Replaced the o-ring and 2 other parts on the intake port (less than $30 from MBZ dealer).
Let us know about these, please.
Thread Starter
Super Member
Joined: Mar 2012
Posts: 535
Likes: 13
From: Franklin, MA
2006 CLK 350/. 2009 CLK 350/2005 Both White
Turns out when I swap the spark plug from six to cly 4 the scan error Read that it’s now four with a misfire, so obviously it’s a bad spark plug. My feeling is that inside the spark plug may have been defective so when it heats up, it creates a good contact that’s why after 10 minutes everything was OK. I’ve installed a new spark plug and I’m testing it now.
Thread Starter
Super Member
Joined: Mar 2012
Posts: 535
Likes: 13
From: Franklin, MA
2006 CLK 350/. 2009 CLK 350/2005 Both White
So I ordered a spark plug. Bosch and I installed it and the problem is fixed. It was a defective spark plug. Apparently, if you put too much load on it, it would fail until it got warmed up and then it would be OK. Once I install the new spark plug, even cold, it didn’t skip no more check engine light problem solved.
Member
Joined: Sep 2020
Posts: 91
Likes: 15
From: Arkansas & California
'00 CLK320, '01 ML320 Designo, '01 ML320 Sport; '04 CLK320 Coupe Avantgar; '04 C230 SportCoupe (HB)
Good to hear that all is set right, and good to know.
Your ah-ha moment I share. (“so I don’t know years and years and years of working on cars. I’ve never had anything like this happen”).
I should more often consider new parts defects.
Your ah-ha moment I share. (“so I don’t know years and years and years of working on cars. I’ve never had anything like this happen”).
I should more often consider new parts defects.
Last edited by Jerry Easley; Jul 24, 2023 at 11:18 PM.
Member
Joined: Sep 2020
Posts: 91
Likes: 15
From: Arkansas & California
'00 CLK320, '01 ML320 Designo, '01 ML320 Sport; '04 CLK320 Coupe Avantgar; '04 C230 SportCoupe (HB)
Curious to know if the title of the thread can now be amended to increase it’s use by others.
”Misfire in cylinder six - new spark plug defective”
”Misfire in cylinder six - new spark plug defective”
Trending Topics
Junior Member
Joined: Dec 2018
Posts: 69
Likes: 6
2000 C280
So I want to add to something I just discovered I decided to swap out spark plugs too so I took out spark plug out a cylinder six and put it in number for spark plug. Number four I put into cylinder six no spark plugs looked identical in wear and tear. I mean seriously they’re only about two weeks old. Well I drove the car until the check engine light came on again and now cylinder two is giving me a misfire no longer cylinder six so it Hass to be a spark plug issue.
Now it doesn’t look fouled it looks super clean. I didn’t see any cracks visibly in the porcelain so I don’t know years and years and years of working on cars. I’ve never had anything like this happened to me were a spark plug failed that was fairly new how is it possible?
please pardon any punctuation and spelling errors. I’m using speech to text while driving to the lake.
Now it doesn’t look fouled it looks super clean. I didn’t see any cracks visibly in the porcelain so I don’t know years and years and years of working on cars. I’ve never had anything like this happened to me were a spark plug failed that was fairly new how is it possible?
please pardon any punctuation and spelling errors. I’m using speech to text while driving to the lake.
even new parts will fail
MB World Stories
The Best of Mercedes & AMG
Manual Mercedes? 6 Times Sindelfingen Let Drivers Have All The Fun
Verdad Gallardo
Mercedes SLR McLaren 722 S Is Extremely Rare Example Modified by McLaren
Verdad Gallardo
8 Classic Boxy Mercedes Designs That Have Aged Like Fine Wine
Verdad Gallardo
Flawlessly Restored Mercedes 190E Evo II Heads to Auction
Verdad Gallardo
Electric Mercedes C-Class Unveiled: 11 Things You Need to Know
Verdad Gallardo
Mercedes EQS Gets A Major Update: Everything You Need to Know
Verdad Gallardo
5 Underrated Mercedes-Benz Models That Don't Get the Love They Deserve
Verdad Gallardo
Mercedes 300D Has Pushed Well Past 1 Million Miles and It Ain't Stopping
Verdad Gallardo
10 Most Reliable Mercedes-Benz Models You Can Buy Used
Verdad Gallardo
Thread Starter
Super Member
Joined: Mar 2012
Posts: 535
Likes: 13
From: Franklin, MA
2006 CLK 350/. 2009 CLK 350/2005 Both White
So what I did was I swap the coil packs and it didn’t help then I replaced the spark plug and that fixed it and the plug was fine
So on the second car when it occurred again, I swapped coil packs and spark plugs, and the check went away. Very bizarre behavior.
So yeah, you can close this, but I would recommend if anybody runs into this swap, the coil packs and the spark plugs and see if that helps
